Datasheets | Clocks and Timing Circuits | Timekeeper | Timekeepers

5V, 256 Kbit (32 Kb x 8) TIMEKEEPER® SRAM

Datasheet

Format: (255 kb)

Last Updated: 06/08/2007

Pages: 29

Features

INTEGRATED, ULTRA LOW POWER SRAM, REAL TIME CLOCK, POWER-FAIL CONTROL CIRCUIT AND BATTERY
BYTEWIDE™ RAM-LIKE CLOCK ACCESS
BCD CODED YEAR, MONTH, DAY, DATE, HOURS, MINUTES, AND SECONDS
FREQUENCY TEST OUTPUT FOR REAL TIME CLOCK
AUTOMATIC POWER-FAIL CHIP DESELECT AND WRITE PROTECTION
WRITE PROTECT VOLTAGES
SELF-CONTAINED BATTERY AND CRYSTAL IN THE CAPHAT™ DIP PACKAGE
SOIC PACKAGE PROVIDES DIRECT CONNECTION FOR A SNAPHAT® HOUSING CONTAINING THE BATTERY AND CRYSTAL
SNAPHAT® HOUSING (BATTERY AND CRYSTAL) IS REPLACEABLE
PIN AND FUNCTION COMPATIBLE WITH JEDEC STANDARD 32 Kb x 8 SRAMs

Related Application Notes

'Negative undershoot' NVRAM data corruption

Battery technology used in NVRAM products from ST

Brand traceability

Predicting the battery life and data retention period of NVRAMs and serial RTCs

Second source for 'Snaphat' by using a dual footprint

TIMEKEEPER® calibration

TIMEKEEPER® rolling into the year 2000 (21st century, Y2K)

Time update in ST's TIMEKEEPER® devices

VMEbus TIMEKEEPER® requirements

Related Datasheets

5V, 256 Kbit (32 Kb x 8) TIMEKEEPER® SRAM

Related Information

NVRAM Home Page

NVRAM Product Page

Non-Volatile RAM (NVRAM) Product Pages

Related Press Releases

Non-Volatile Clock/RAM for Industrial Applications

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M48T35 M48T35Y
5V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM
Features

Integrated, ultra low power SRAM, real time clock, power-fail control circuit and battery BYTEWIDETM RAM-like clock access BCD coded year, month, day, date, hours, minutes, and seconds
28

Frequency test output for real time clock Automatic power-fail chip deselect and WRITE protection WRITE protect voltages (VPFD = Power-fail Deselect Voltage): M48T35: VCC = 4.75 to 5.5V 4.5V VPFD 4.75V M48T35Y: VCC = 4.5 to 5.5V 4.2V VPFD 4.5V

1

PCDIP28 (PC) Battery/Crystal CAPHAT

SNAPHAT (SH) Battery/Crystal

Self-contained battery and crystal in the CAPHATTM DIP package SOIC package provides direct connection for a SNAPHAT housing containing the battery and crystal SNAPHAT housing (battery and crystal) is replaceable Pin and function compatible with JEDEC standard 32 Kb x 8 SRAMs RoHS compliant Lead-free second level interconnect
28 1

SOH28 (MH)

August 2007

Rev 7

1/29
www.st.com 1

Contents

M48T35 M48T35Y

Contents
1 2 Summary description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Operation modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 2.2 2.3 Read mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Write mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3

Clock operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1 3.2 3.3 3.4 3.5 3.6 Reading the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Setting the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Stopping and starting the oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Calibrating the clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Century bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 VCC noise and negative going transients . . . . . . . . . . . . . . . . . . . . . . . . . 15

4 5 6 7 8

Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 DC and AC parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Package mechanical information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

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M48T35 M48T35Y

List of tables

List of tables
Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. Table 14. Table 15. Table 16. Table 17. Table 18. Table 19. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Read mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Write mode AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Operating and AC measurement conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 DC characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Power down/up AC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Power down/up trip points DC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 PCDIP28 28-pin plastic DIP, battery CAPHAT, package mechanical data . . . . . . . . . . . 21 SOH28 28-lead plastic SO, 4-socket battery SNAPHAT, package mechanical data . . . 22 SH 4-pin SNAPHAT housing for 48mAh battery & crystal, package mechanical data . . 23 SH 4-pin SNAPHAT housing for 120mAh battery & crystal, package mechanical data . 24 PMDIP28 28-pin plastic DIP, hybrid, package mechanical data . . . . . . . . . . . . . . . . . . . 25 Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 SNAPHAT battery table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

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List of figures

M48T35 M48T35Y

List of figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 DIP connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Read mode AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Write enable controlled, write AC waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Chip enable controlled, write AC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Crystal accuracy across temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Clock calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Supply voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 AC measurement load circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Power down/up mode AC waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 PCDIP28 28-pin plastic DIP, battery CAPHAT, package outline . . . . . . . . . . . . . . . . . . . 21 SOH28 28-lead plastic small outline, 4-socket battery SNAPHAT, package outline . . . . 22 SH 4-pin SNAPHAT housing for 48mAh battery & crystal, package outline . . . . . . . . . . 23 SH 4-pin SNAPHAT housing for 120mAh battery & crystal, package outline . . . . . . . . . 24 PMDIP28 28-pin plastic DIP, hybrid, package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

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M48T35 M48T35Y

Summary description

1

Summary description
The M48T35/Y TIMEKEEPER RAM is a 32Kb x 8 non-volatile static RAM and real time clock. The monolithic chip is available in two special packages to provide a highly integrated battery backed-up memory and real time clock solution. The M48T35/Y is a non-volatile pin and function equivalent to any JEDEC standard 32Kb x 8 SRAM. It also easily fits into many ROM, EPROM, and EEPROM sockets, providing the non-volatility of PROMs without any requirement for special WRITE timing or limitations on the number of WRITEs that can be performed. The 28-pin, 600mil DIP CAPHAT houses the M48T35/Y silicon with a quartz crystal and a long life lithium button cell in a single package. The 28-pin, 330mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT housing containing the battery and crystal. The unique design allows the SNAPHAT battery package to be mounted on top of the SOIC package after the completion of the surface mount process. Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal damage due to the high temperatures required for device surface-mounting. The SNAPHAT housing is keyed to prevent reverse insertion. The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or in Tape & Reel form. For the 28-lead SOIC, the battery/crystal package (e.g., SNAPHAT) part number is "M4T28BR12SH" (see Table 18 on page 27).

Figure 1.

Logic diagram
VCC

15 A0-A14

8 DQ0-DQ7

W E G

M48T35 M48T35Y

VSS

AI01620B

5/29

Summary description Table 1.
A0-A14 DQ0-DQ7 E G W VCC VSS

M48T35 M48T35Y Signal names
Address inputs Data inputs / outputs Chip enable Output enable WRITE Enable Supply voltage Ground

Figure 2.

DIP connections
A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 1 2 3 4 5 6 7 M48T35 8 M48T35Y 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3

AI01621B

Figure 3.

SOIC connections
A14 A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 1 2 3 4 5 6 7 M48T35Y 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VCC W A13 A8 A9 A11 G A10 E DQ7 DQ6 DQ5 DQ4 DQ3

AI01622B

6/29

M48T35 M48T35Y Figure 4. Block diagram

Summary description

OSCILLATOR AND CLOCK CHAIN 32,768 Hz CRYSTAL POWER

8 x 8 BiPORT SRAM ARRAY

A0-A14

32,760 x 8 SRAM ARRAY LITHIUM CELL VOLTAGE SENSE AND SWITCHING CIRCUITRY VPFD

DQ0-DQ7

E W G

VCC

VSS

AI01623

7/29

Operation modes

M48T35 M48T35Y

2

Operation modes
As Figure 4 on page 7 shows, the static memory array and the quartz controlled clock oscillator of the M48T35/Y are integrated on one silicon chip. The two circuits are interconnected at the upper eight memory locations to provide user accessible BYTEWIDE clock information in the bytes with addresses 7FF8h-7FFFh. The clock locations contain the year, month, date, day, hour, minute, and second in 24 hour BCD format. Corrections for 28, 29 (leap year - valid until 2100), 30, and 31 day months are made automatically. Byte 7FF8h is the clock control register. This byte controls user access to the clock information and also stores the clock calibration setting. The eight clock bytes are not the actual clock counters themselves; they are memory locations consisting of BiPORTTM READ/WRITE memory cells. The M48T35/Y includes a clock control circuit which updates the clock bytes with current information once per second. The information can be accessed by the user in the same manner as any other location in the static memory array. The M48T35/Y also has its own Power-fail Detect circuit. The control circuitry constantly monitors the single 5V supply for an out of tolerance condition. When VCC is out of tolerance, the circuit write protects the SRAM, providing a high degree of data security in the midst of unpredictable system operation brought on by low VCC. As VCC falls below the Battery Back-up Switchover Voltage (VSO), the control circuitry connects the battery which maintains data and clock operation until valid power returns. Table 2.
Mode Deselect WRITE READ READ Deselect Deselect VSO to VPFD (min)(1) VSO(1) 4.75 to 5.5V or 4.5 to 5.5V

Operating modes
VCC E VIH VIL VIL VIL X X G X X VIL VIH X X W X VIL VIH VIH X X DQ0-DQ7 High Z DIN DOUT High Z High Z High Z Power Standby Active Active Active CMOS Standby Batter y Back-up Mode

1. See Table 11 on page 20 for details.

Note:

X = VIH or VIL; VSO = Battery Back-up Switchover Voltage.

2.1

Read mode
The M48T35/Y is in the READ Mode whenever W (WRITE Enable) is high and E (Chip Enable) is low. The unique address specified by the 15 Address Inputs defines which one of the 32,768 bytes of data is to be accessed. Valid data will be available at the Data I/O pins within Address Access time (tAVQV) after the last address input signal is stable, providing that the E and G access times are also satisfied. If the E and G access times are not met, valid data will be available after the latter of the Chip Enable Access time (tELQV) or Output Enable Access time (tGLQV). The state of the eight three-state Data I/O signals is controlled by E and G. If the outputs are activated before tAVQV, the data lines will be driven to an indeterminate state until tAVQV.

8/29

M48T35 M48T35Y

Operation modes

If the Address Inputs are changed while E and G remain active, output data will remain valid for Output Data Hold time (tAXQX) but will go indeterminate until the next Address Access. Figure 5. Read mode AC waveforms
tAVAV A0-A14 tAVQV tELQV E tELQX tGLQV G tGLQX DQ0-DQ7 VALID
AI00925

VALID tAXQX tEHQZ

tGHQZ

Note: Table 3.
Symbol tAVAV tAVQV tELQV tGLQV tELQX(2) tGLQX(2) tEHQZ
(2)

WRITE Enable (W) = High. Read mode AC characteristics
Parameter(1) Min READ Cycle Time Address Valid to Output Valid Chip Enable Low to Output Valid Output Enable Low to Output Valid Chip Enable Low to Output Transition Output Enable Low to Output Transition Chip Enable High to Output Hi-Z Output Enable High to Output Hi-Z Address Transition to Output Transition 10 5 5 25 25 70 70 70 35 M48T35/Y Unit Max ns ns ns ns ns ns ns ns ns

tGHQZ(2) tAXQX

1. Valid for Ambient Operating Temperature: TA = 0 to 70 or 40 to 85C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted). 2. CL = 5pF.

2.2

Write mode
The M48T35/Y is in the WRITE Mode whenever W and E are low. The start of a WRITE is referenced from the latter occurring falling edge of W or E. A WRITE is terminated by the earlier rising edge of W or E. The addresses must be held valid throughout the cycle. E or W must return high for a minimum of tEHAX from Chip Enable or tWHAX from WRITE Enable prior to the initiation of another READ or WRITE Cycle. Data-in must be valid tDVWH prior to the end of WRITE and remain valid for tWHDX afterward. G should be kept high during

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Operation modes

M48T35 M48T35Y

WRITE Cycles to avoid bus contention; although, if the output bus has been activated by a low on E and G, a low on W will disable the outputs tWLQZ after W falls. Figure 6. Write enable controlled, write AC waveform
tAVAV A0-A14 VALID tAVWH tAVEL E tWLWH tAVWL W tWLQZ tWHDX DQ0-DQ7 DATA INPUT tDVWH
AI00926

tWHAX

tWHQX

Figure 7.

Chip enable controlled, write AC waveforms
tAVAV A0-A14 VALID tAVEH tAVEL E tAVWL W tEHDX DQ0-DQ7 DATA INPUT tDVEH
AI00927

tELEH

tEHAX

Table 4.
Symbol tAVAV tAVWL tAVEL

Write mode AC characteristics
Parameter(1) Min WRITE Cycle Time Address Valid to WRITE Enable Low Address Valid to Chip Enable Low 70 0 0 M48T35/Y Unit Max ns ns ns

10/29

M48T35 M48T35Y Table 4.
Symbol tWLWH tELEH tWHAX t EHAX tDVWH tDVEH tWHDX t EHDX tWLQZ
(2)(3)

Operation modes

Write mode AC characteristics (continued)
Parameter(1) Min WRITE Enable Pulse Width Chip Enable Low to Chip Enable High WRITE Enable High to Address Transition Chip Enable High to Address Transition Input Valid to WRITE Enable High Input Valid to Chip Enable High WRITE Enable High to Input Transition Chip Enable High to Input Transition WRITE Enable Low to Output Hi-Z Address Valid to WRITE Enable High Address Valid to Chip Enable High WRITE Enable High to Output Transition 60 60 5 50 55 0 0 30 30 5 5 25 M48T35/Y Unit Max ns ns ns ns ns ns ns ns ns ns ns ns

tAVWH tAVEH tWHQX(2)(3)

1. Valid for Ambient Operating Temperature: TA = 0 to 70 or 40 to 85C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted). 2. CL = 5pF. 3. If E goes low simultaneously with W going low, the outputs remain in the high impedance state.

2.3

Data retention mode
With valid VCC applied, the M48T35/Y operates as a conventional BYTEWIDE static RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write protecting itself when VCC falls within the VPFD (max), VPFD (min) window. All outputs become high impedance, and all inputs are treated as "Don't care" (see Figure 12 on page 19, Table 10, and Table 11 on page 20).

Note:

A power failure during a WRITE cycle may corrupt data at the currently addressed location, but does not jeopardize the rest of the RAM's content. At voltages below VPFD (min), the user can be assured the memory will be in a write protected state, provided the VCC fall time is not less than tF. The M48T35/Y may respond to transient noise spikes on VCC that reach into the deselect window during the time the device is sampling VCC. Therefore, decoupling of the power supply lines is recommended. When VCC drops below VSO, the control circuit switches power to the internal battery which preserves data and powers the clock. The internal button cell will maintain data in the M48T35/Y for an accumulated period of at least 7 years when VCC is less than VSO. As system power returns and VCC rises above VSO, the battery is disconnected, and the power supply is switched to external VCC. Write protection continues until VCC reaches VPFD (min) plus trec (min). E should be kept high as VCC rises past VPFD (min) to prevent inadvertent WRITE Cycles prior to processor stabilization. Normal RAM operation can resume trec after VCC exceeds VPFD (max). For more information on Battery Storage Life refer to the Application Note AN1012.

11/29

Clock operations

M48T35 M48T35Y

3
3.1

Clock operations
Reading the clock
Updates to the TIMEKEEPER registers (see Table 5) should be halted before clock data is read to prevent reading data in transition. The BiPORTTM TIMEKEEPER cells in the RAM array are only data registers and not the actual clock counters, so updating the registers can be halted without disturbing the clock itself. Updating is halted when a '1' is written to the READ Bit, D6 in the Control Register 7FF8h. As long as a '1' remains in that position, updating is halted. After a halt is issued, the registers reflect the count; that is, the day, date, and the time that were current at the moment the halt command was issued. All of the TIMEKEEPER registers are updated simultaneously. A halt will not interrupt an update in progress. Updating is within a second after the bit is reset to a '0.'

3.2

Setting the clock
Bit D7 of the Control Register 7FF8h is the WRITE Bit. Setting the WRITE Bit to a '1,' like the READ Bit, halts updates to the TIMEKEEPER registers. The user can then load them with the correct day, date, and time data in 24 hour BCD format (see Table 5). Resetting the WRITE Bit to a '0' then transfers the values of all time registers 7FF9h-7FFFh to the actual TIMEKEEPER counters and allows normal operation to resume. The FT Bit and the bits marked as '0' in Table 5 must be written to '0' to allow for normal TIMEKEEPER and RAM operation. After the WRITE Bit is reset, the next clock update will occur within one second. See the Application Note AN923, "TIMEKEEPER Rolling Into the 21st Century" for information on Century Rollover.

3.3

Stopping and starting the oscillator
The oscillator may be stopped at any time. If the device is going to spend a significant amount of time on the shelf, the oscillator can be turned off to minimize current drain on the battery. The STOP Bit is the MSB of the seconds register. Setting it to a '1' stops the oscillator. The M48T35/Y is shipped from STMicroelectronics with the STOP Bit set to a '1.' When reset to a '0,' the M48T35/Y oscillator starts within 1 second.

12/29

M48T35 M48T35Y Table 5.
Address D7 7FFFh 7FFEh 7FFDh 7FFCh 7FFBh 7FFAh
7FF9h 7FF8h

Clock operations Register map
Data D6 D5 D4 D3 D2 D1 Year 10 M. Month Date 0 Day Hours Minutes
Seconds Calibration

Function/Range D0 BCD Format Year Month Date Centur y/ Day Hours Minutes
Seconds Control

10 Years 0 0 0 0 0
ST W R

00-99 01-12 01-31 00-01/0107 00-23 00-59
00-59

0 0 FT 0

0

10 Date CEB CB

10 Hours 10 Minutes
10 Seconds S

Keys: S = SIGN Bit FT = FREQUENCY TEST Bit (Must be set to '0' upon power for normal operation) R = READ Bit W = WRITE Bit ST = STOP Bit 0 = Must be set to '0' CEB = Century Enable Bit CB = Century Bit Note: When CEB is set to '1,' CB will toggle from '0' to '1' or from '1' to '0' at the turn of the century (dependent upon the initial value set). When CEB is set to '0,' CB will not toggle. The WRITE Bit does not need to be set to write to CEB.

3.4

Calibrating the clock
The M48T35/Y is driven by a quartz-controlled oscillator with a nominal frequency of 32,768 Hz. The devices are tested not to exceed 35 ppm (parts per million) oscillator frequency error at 25C, which equates to about 1.53 minutes per month. With the calibration bits properly set, the accuracy of each M48T35/Y improves to better than +1/2 ppm at 25C. The oscillation rate of any crystal changes with temperature (see Figure 8 on page 15). Most clock chips compensate for crystal frequency and temperature shift error with cumbersome "trim" capacitors. The M48T35/Y design, however, employs periodic counter correction. The calibration circuit adds or subtracts counts from the oscillator divider circuit at the divide by 256 stage, as shown in Figure 9 on page 15. The number of times pulses are blanked (subtracted, negative calibration) or split (added, positive calibration) depends upon the value loaded into the five calibration bits found in the Control Register. Adding counts speeds the clock up, subtracting counts slows the clock down. The Calibration Byte occupies the five lower order bits (D4-D0) in the Control Register 7FF8h. These bits can be set to represent any value between 0 and 31 in binary form. Bit D5 is the Sign Bit; '1' indicates positive calibration, '0' indicates negative calibration. Calibration occurs within a 64 minute cycle. The first 62 minutes in the cycle may, once per

13/29

Clock operations

M48T35 M48T35Y

minute, have one second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary '1' is loaded into the register, only the first 2 minutes in the 64 minute cycle will be modified; if a binary 6 is loaded, the first 12 will be affected, and so on. Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator cycles for every 125,829,120 actual oscillator cycles, that is +4.068 or 2.034 ppm of adjustment per calibration step in the calibration register. Assuming that the oscillator is in fact running at exactly 32,768 Hz, each of the 31 increments in the Calibration Byte would represent +10.7 or 5.35 seconds per month which corresponds to a total range of +5.5 or 2.75 minutes per month. Two methods are available for ascertaining how much calibration a given M48T35/Y may require. The first involves simply setting the clock, letting it run for a month and comparing it to a known accurate reference (like WWV broadcasts). While that may seem crude, it allows the designer to give the end user the ability to calibrate his clock as his environment may require, even after the final product is packaged in a non-user serviceable enclosure. All the designer has to do is provide a simple utility that accesses the Calibration Byte. The second approach is better suited to a manufacturing environment, and involves the use of some test equipment. When the Frequency Test (FT) Bit, the seventh-most significant bit in the Day Register is set to a '1,' and D7 of the Seconds Register is a '0' (Oscillator Running), DQ0 will toggle at 512 Hz during a READ of the Seconds Register. Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.01024 Hz would indicate a +20 ppm oscillator frequency error, requiring a 10 (WR001010) to be loaded into the Calibration Byte for correction. Note: Setting or changing the Calibration Byte does not affect the Frequency Test output frequency. The FT Bit MUST be reset to '0' for normal clock operations to resume. The FT Bit is automatically Reset on power-down. For more information on calibration, see Application Note AN934, "TIMEKEEPER Calibration."

3.5

Century bit
Bit D5 and D4 of Clock Register 1FFCh contain the CENTURY ENABLE Bit (CEB) and the CENTURY Bit (CB). Setting CEB to a '1' will cause CB to toggle, either from a '0' to '1' or from '1' to '0' at the turn of the century (depending upon its initial state). If CEB is set to a '0,' CB will not toggle.

Note:

The WRITE Bit must be set in order to write to the CENTURY Bit.

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M48T35 M48T35Y Figure 8. Crystal accuracy across temperature
ppm 20

Clock operations

0

-20

-40 F = -0.038 ppm (T - T )2 10% 0 F C2 T0 = 25 C -80

-60

-100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 C

AI02124

Figure 9.
NORMAL

Clock calibration

POSITIVE CALIBRATION

NEGATIVE CALIBRATION
AI00594B

3.6

VCC noise and negative going transients
ICC transients, including those produced by output switching, can produce voltage fluctuations, resulting in spikes on the VCC bus. These transients can be reduced if capacitors are used to store energy which stabilizes the VCC bus. The energy stored in the bypass capacitors will be released as low going spikes are generated or energy will be absorbed when overshoots occur. A bypass capacitor value of 0.1F (as shown in Figure 10 on page 16) is recommended in order to provide the needed filtering. In addition to transients that are caused by normal SRAM operation, power cycling can generate negative voltage spikes on VCC that drive it to values below VSS by as much as one volt. These negative spikes can cause data corruption in the SRAM while in battery backup mode. To protect from these voltage spikes, it is recommended to connect a schottky diode from VCC to VSS (cathode connected to VCC, anode to VSS). Schottky diode

15/29

Clock operations

M48T35 M48T35Y

1N5817 is recommended for through hole and MBRS120T3 is recommended for surface mount. Figure 10. Supply voltage protection
VCC VCC

0.1F

DEVICE

VSS

AI02169

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M48T35 M48T35Y

Maximum rating

4

Maximum rating
Stressing the device above the rating listed in the "Absolute Maximum Ratings" table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the Operating sections of this specification is not implied. Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability. Refer also to the STMicroelectronics SURE Program and other relevant quality documents. Table 6.
Symbol TA TSTG TSLD
(1)(2)(3)

Absolute maximum ratings
Parameter Ambient Operating Temperature Grade 1 Grade 6 Value 0 to 70 40 to 85 40 to 85 260 M48T35 M48T35Y M48T35 M48T35Y 0.3 to 7 0.3 to 7 0.3 to 7 0.3 to 7 20 1 Unit C C C C V V V V mA W

Storage Temperature (VCC Off, Oscillator Off) Lead Solder Temperature for 10 seconds Input or Output Voltages Supply Voltage Output Current Power Dissipation

VIO VCC IO PD

1. For DIP package: Soldering temperature not to exceed 260C for 10 seconds (total thermal budget not to exceed 150C for longer than 30 seconds). 2. For SO package, standard (SnPb) lead finish: Reflow at peak temperature of 225C (total thermal budget not to exceed 180C for between 90 to 150 seconds). 3. For SO package, Lead-free (Pb-free) lead finish: Reflow at peak temperature of 260C (total thermal budget not to exceed 245C for greater than 30 seconds).

Caution: Caution:

Negative undershoots below 0.3V are not allowed on any pin while in the Battery Back-up mode. Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets.

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DC and AC parameters

M48T35 M48T35Y

5

DC and AC parameters
This section summarizes the operating and measurement conditions, as well as the DC and AC characteristics of the device. The parameters in the following DC and AC Characteristic tables are derived from tests performed under the Measurement Conditions listed in the relevant tables. Designers should check that the operating conditions in their projects match the measurement conditions when using the quoted parameters. Table 7. Operating and AC measurement conditions
Parameter Supply Voltage (VCC) Ambient Operating Temperature (TA) Load Capacitance (CL) Input Rise and Fall Times Input Pulse Voltages Input and Output Timing Ref. Voltages M48T35 4.75 to 5.5 0 to 70 100 5 0 to 3 1.5 M48T35Y 4.5 to 5.5 40 to 85 100 5 0 to 3 1.5 Unit V C pF ns V V

Note:

Output Hi-Z is defined as the point where data is no longer driven. Figure 11. AC measurement load circuit
5V

1.9k DEVICE UNDER TEST 1k

OUT

CL = 100pF or 5pF

CL includes JIG capacitance

AI01030

Table 8.
Symbol CIN COUT(3)
1. 2. 3.

Capacitance
Parameter(1)(2) Input Capacitance Output Capacitance Min Max 10 10 Unit pF pF

Effective capacitance measured with power supply at 5V; sampled only, not 100% tested. At 25C, f = 1MHz. Outputs deselected.

18/29

M48T35 M48T35Y Table 9.
Symbol ILI ILO(2)(2) ICC ICC1 ICC2 VIL VIH VOL VOH

DC and AC parameters

DC characteristics
Parameter Input Leakage Current Output Leakage Current Supply Current Supply Current (Standby) TTL Supply Current (Standby) CMOS Input Low Voltage Input High Voltage Output Low Voltage Output High Voltage IOL = 2.1mA IOH = 1mA 2.4 Test condition(1) 0V VIN VCC 0V VOUT VCC Outputs open E = VIH E = VCC 0.2V 0.3 2.2 M48T35 Min Max 1 1 50 3 2 0.8 VCC + 0.3 0.4 2.4 0.3 2.2 M48T35Y Unit Min Max 1 1 30 3 2 0.8 VCC + 0.3 0.4 A A mA mA mA V V V V

1. Valid for Ambient Operating Temperature: TA = 0 to 70 or 40 to 85C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted). 2. Outputs deselected.

Figure 12. Power down/up mode AC waveforms
VCC VPFD (max) VPFD (min) VSO tF tFB tPD INPUTS
RECOGNIZED

tR tRB tDR DON'T CARE trec
RECOGNIZED

HIGH-Z OUTPUTS VALID
(PER CONTROL INPUT)

VALID
(PER CONTROL INPUT)

AI01168C

19/29

DC and AC parameters Table 10.
Symbol tPD tF
(2)

M48T35 M48T35Y

Power down/up AC characteristics
Parameter(1) E or W at VIH before Power Down VPFD (max) to VPFD (min) VCC Fall Time VPFD (min) to VSS VCC Fall Time VPFD (min) to VPFD (max) VCC Rise Time VSS to VPFD (min) VCC Rise Time VPFD (max) to Inputs Recognized M48T35 M48T35Y Min 0 300 10 10 10 1 40 200 Max Unit s s s s s s ms

tFB(3) tR tRB trec(4)(4)

1. Valid for Ambient Operating Temperature: TA = 0 to 70 or 40 to 85C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted). 2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200s after VCC passes VPFD (min). 3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data. 4. trec (min) = 20ms for industrial temperature Grade 6 device.

Table 11.
Symbol VPFD VSO tDR(3)(5)

Power down/up trip points DC characteristics
Parameter(1)(2) Power-fail Deselect Voltage M48T35 M48T35Y M48T35 M48T35Y Grade 1 Grade 6 10(4) 10(5) Min 4.5 4.2 Typ 4.6 4.35 3.0 3.0 Max 4.75 4.5 Unit V V V V YEARS YEARS

Batter y Back-up Switchover Voltage

Expected Data Retention Time

1. Valid for Ambient Operating Temperature: TA = 0 to 70 or 40 to 85C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted). 2. All voltages referenced to VSS. 3. CAPHAT and M4T32-BR12SH1 SNAPHAT only, M4T28-BR12SH1 SNAPHAT top tDR = 7 years (typ). 4. Using larger M4T32-BR12SH6 SNAPHAT top (recommended for Industrial Temperature Range - Grade 6 device). 5. At 25C, VCC = 0V.

20/29

M48T35 M48T35Y

Package mechanical information

6

Package mechanical information
In order to meet environmental requirements, ST offers these devices in ECOPACK packages. These packages have a Lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com. Figure 13. PCDIP28 28-pin plastic DIP, battery CAPHAT, package outline

A2

A

A1 B1 B e3 D
N

L eA

C

e1

E
1 PCDIP

Note:

Drawing is not to scale. Table 12.
Symbol Typ A A1 A2 B B1 C D E e1 e3 eA L N Min 8.89 0.38 8.38 0.38 1.14 0.20 39.37 17.83 2.29 29.72 15.24 3.05 28 Max 9.65 0.76 8.89 0.53 1.78 0.31 39.88 18.34 2.79 36.32 16.00 3.81 Typ Min 0.350 0.015 0.330 0.015 0.045 0.008 1.550 0.702 0.090 1.170 0.600 0.120 28 Max 0.380 0.030 0.350 0.021 0.070 0.012 1.570 0.722 0.110 1.430 0.630 0.150

PCDIP28 28-pin plastic DIP, battery CAPHAT, package mechanical data
mm inches

21/29

Package mechanical information

M48T35 M48T35Y

Figure 14. SOH28 28-lead plastic small outline, 4-socket battery SNAPHAT, package outline

A2 B e

A C eB CP

D
N

E

H A1 L

1 SOH-A

Note:

Drawing is not to scale. Table 13. SOH28 28-lead plastic SO, 4-socket battery SNAPHAT, package mechanical data
mm Symbol Typ A A1 A2 B C D E e eB H L a N CP 1.27 0.05 2.34 0.36 0.15 17.71 8.23 3.20 11.51 0.41 0 28 0.10 Min Max 3.05 0.36 2.69 0.51 0.32 18.49 8.89 3.61 12.70 1.27 8 0.050 0.002 0.092 0.014 0.006 0.697 0.324 0.126 0.453 0.016 0 28 0.004 Typ Min Max 0.120 0.014 0.106 0.020 0.012 0.728 0.350 0.142 0.500 0.050 8 inches

22/29

M48T35 M48T35Y

Package mechanical information

Figure 15. SH 4-pin SNAPHAT housing for 48mAh battery & crystal, package outline

A1

A2 A A3

eA D

B eB

L

E

SHTK

Note:

Drawing is not to scale. Table 14. SH 4-pin SNAPHAT housing for 48mAh battery & crystal, package mechanical data
mm Symbol Typ A A1 A2 A3 B D E eB L 0.46 21.21 14.22 3.20 2.03 6.73 6.48 Min Max 9.78 7.24 6.99 0.38 0.56 21.84 14.99 3.61 2.29 0.018 0.835 0.560 0.126 0.080 0.265 0.255 Typ Min Max 0.385 0.285 0.275 0.015 0.022 0.860 0.590 0.142 0.090 inches

23/29

Package mechanical information

M48T35 M48T35Y

Figure 16. SH 4-pin SNAPHAT housing for 120mAh battery & crystal, package outline

A1

A2 A A3

eA D

B eB

L

E

SHTK

Note:

Drawing is not to scale. Table 15. SH 4-pin SNAPHAT housing for 120mAh battery & crystal, package mechanical data
mm Symbol Typ A A1 A2 A3 B D E eB L 0.46 21.21 17.27 3.20 2.03 8.00 7.24 Min Max 10.54 8.51 8.00 0.38 0.56 21.84 18.03 3.61 2.29 0.018 0.835 0.680 0.126 0.080 0.315 0.285 Typ Min Max 0.415 0.335 0.315 0.015 0.022 0.860 0.710 0.142 0.090 inches

24/29

M48T35 M48T35Y

Package mechanical information

Figure 17. PMDIP28 28-pin plastic DIP, hybrid, package outline

A

A1 S B e3 D e1

L eA

C

N

E
1 PMDIP

Note:

Drawing is not to scale. Table 16.
Symbol Typ A A1 B C D E e1 e3 eA L S N 33.02 14.99 3.05 1.91 28 16.00 3.81 2.67 Min 9.27 0.38 0.43 0.20 37.34 18.03 2.29 0.58 0.33 37.85 18.80 2.79 1.300 0.590 0.120 0.075 28 0.630 0.150 0.105 Max 9.53 Typ Min 0.365 0.015 0.017 0.008 1.470 0.710 0.090 0.023 0.013 1.490 0.740 0.110 Max 0.375

PMDIP28 28-pin plastic DIP, hybrid, package mechanical data
mm inches

25/29

Part numbering

M48T35 M48T35Y

7

Part numbering
Table 17.
Example: Device type M48T Supply voltage and write protect voltage 35(1) = VCC = 4.75 to 5.5V; VPFD = 4.5 to 4.75V 35Y = VCC = 4.5 to 5.5V; VPFD = 4.2 to 4.5V Speed 70 = 70ns Package PC = PCDIP28 MH(2) = SOH28 PM = PMDIP28 (NND)(3) Temperature range 1 = 0 to 70C 6 = 40 to 85C(4) Shipping method For SOH28: blank = Tubes (Not for New Design - Use E) E = ECOPACK package, tubes F = ECOPACK package, tape & reel TR = Tape & Reel (Not for New Design - Use F) For PCDIP28: blank = ECOPACK package, tubes
1. The M48T35 part is offered with the PCDIP28 (e.g., CAPHAT) package only. 2. The SOIC package (SOH28) requires the SNAPHAT battery package which is ordered separately under the part number "M4TXX-BR12SH" in plastic tube or "M4TXX-BR12SHTR" in Tape & Reel form (see Table 18 on page 27). 3. This package is not to be used for New Design. 4. Available in SOIC package only.

Ordering information scheme
M48T 35 70 PC 1 E

Caution:

Do not place the SNAPHAT battery package "M4TXX-BR12SH" in conductive foam as it will drain the lithium button-cell battery. For other options, or for more information on any aspect of this device, please contact the ST sales office nearest you.

26/29

M48T35 M48T35Y Table 18. SNAPHAT battery table
Description Lithium Battery (48mAh) SNAPHAT Lithium Battery (120mAh) SNAPHAT

Part numbering

Part number M4T28-BR12SH M4T32-BR12SH

Package SH SH

27/29

Revision history

M48T35 M48T35Y

8

Revision history
Table 19.
Date Nov- 1999 07-Feb-2000 04-Jun-2001 31-Jul-2001 06-Mar-2002 20-May-2002 26-Jun-2002 31-Mar-2003 10-Dec-2003 31-Mar-2004 05-Dec20-05 01-Aug-2007

Document revision history
Revision 1.0 1.1 2.0 2.1 2.2 2.3 2.4 3.0 4.0 5.0 6.0 7.0 First Issue tDR Description changed (Table 9) Reformatted; temp/voltage info. added to tables (Table 8, 9, 3, 4, 10, 11); add Century Bit text Formatting changes based on latest document reviews Add PMDIP Packaging option, which is "Not for New Design" (NND) (Table 17, 16, and Figure 17) Modify reflow time and temperature footnotes (Table 6) Add footnote to table (Table 11) v2.2 template applied; data retention condition updated (Table 11) Reformatted; update DC Characteristics (Table 9) Reformatted; update Pb-free package information (Table 6, 17) Updated template, Lead-free text, and remove footnote (Table 9, 17) Reformatted; added lead-free second level interconnect information to cover page and Section 6: Package mechanical information. Changes

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M48T35 M48T35Y

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Document Number: 2611



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