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Step - Down
1.5A step down switching regulator
Datasheet
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Last Updated: 13/05/2008
Pages: 13
Related Application Notes
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L4971
1.5A STEP DOWN SWITCHING REGULATOR
1
FEATURES
UP TO 1.5A STEP DOWN CONVERTER OPERATING INPUT VOLTAGE FROM 8V TO 55V PRECISE 3.3V (1%) INTERNAL REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 3.3V TO 50V SWITCHING FREQUENCY ADJUSTABLE UP TO 300KHz VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION INTERNAL CURRENT LIMITING (PULSEBYPULSE AND HICCUP MODE) INHIBIT FOR ZERO CURRENT CONSUMPTION PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN SOFT START FUNCTION
Figure 1. Package
DIP8
SO16W
Table 1. Order Codes
Part Number L4971 L4971D L4971D013TR Package DIP8 SO 16W SO16 in Tape & Reel
A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8V to 55V and output voltages regulated from 3.3V to 50V cover the majority of today's applications. Features of this new generations of DC-DC converter include pulse-by-pulse current limit, hiccup mode for short circuit protection, voltage feedforward regulation, soft-start, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. The device is available in plastic dual in line, DIP8 for standard assembly, and SO16W for SMD assembly .
2
DESCRIPTION
The L4971 is a step down monolithic power switching regulator delivering 1.5A at a voltage between 3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device uses an internal power D-MOS transistor (with a typical Rdson of 0.25) to obtain very high efficency and high switching speed. Figure 1. Block Diagram
Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7
8
L4971
4 1 6 L1 126H (77120) D1 STPS 3L60U C8 330F VO=3.3V/1.5A
C5 100nF
R2 9.1K C4 22nF
C6 100nF
D97IN748A
May 2005
Rev. 11 1/13
L4971
Figure 2. Block Diagram
VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE SS_INH 2 INHIBIT SOFTSTART 3.3V COMP FB 7 8 E/A INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 6 PWM BOOT
R S
3.3V
Q DRIVE
OSCILLATOR 1 GND
CBOOT CHARGE AT LIGHT LOADS
3 OSC
4 OUT
D97IN594
Figure 3. Pin Connections
N.C. GND 1 2 3 4 5 6 7 8
D97IN596
16 15 14 13 12 11 10 9
N.C. N.C. FB COMP BOOT VCC N.C. N.C.
GND SS_INH OSC OUT
1 2 3 4
D97IN595
8 7 6 5
FB COMP BOOT VCC
SS_INH OSC OUT OUT N.C. N.C.
DIP8
SO16
Table 2. Pin Description
DIP 1 2 SO (*) 2 3 N ame GND SS_IN H Gr o u n d A logic signal (active low) disables the device (sleep mode operation). A capacitor connected between this pin and ground determines the soft start time. When this pin is grounded disabled the device (driven by open collector/drain). An external resistor connected between the unregulated input voltage and this pin and a capacitor connected from this pin to ground fix the switching frequency. (Line feed forward is automatically obtained) Stepdown regulator output Unregulated DC input voltage A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistor E/A output to be used for frequency compensation Stepdown feedback input. Connecting directly to this pin results in an output voltage of 3.3V. An external resistive divider is required for higher output voltages. Function
3
4
OSC
4 5 6 7 8
5, 6 11 12 13 14
OU T
VCC
BOOT C O MP FB
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
2/13
L4971
Table 3. Absolute Maximum Ratings
Symbol Minidip V5 V4 I4 V6-V5 V6 V7 V2 V8 Ptot Tj,Tstg S016 V11 V5,V6 I5,I6 V12-V11 V12 V13 V3 V14 Bootstrap voltage Analogs input voltage (VCC = 24V Analogs input voltage (VCC = 24V) (VCC = 20V) Power dissipation a Tamb 60C Junction and storage temperature DIP8 S O1 6 Input voltage Output DC voltage Output peak voltage at t = 0.1s f=200KHz Maximum output current Parameter Value 58 -1 -5 int. limit. 14 70 12 13 6 -0.3 1 0.8 -40 to 150 V V V V V V W W C Unit V V V
Table 4. Thermal Data
Symbol Rth(j-amb) Parameter Thermal Resistance Junction to ambient Max. DIP8 90 (*) SO16 110 (*) Unit C/W
(*) Package mounted on board.
3
ELECTRICAL CHARACTERISTCS
Table 5. (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125C
Symbol Parameter Test Condition Min. Typ. Max. Unit
DYNAMIC CHARACTERISTIC VI Vo Operating input voltage range Output voltage Vo = 3.3 to 50V; Io = 1.5A Io = 0.5A Io = 0.2 to 1.5A Vcc = 8 to 55V Vd Dropout voltage Vcc = 10V; Io = 1.5A * Il Maximum limiting current Efficiency Switching frequency Supply voltage ripple rejection Voltage stability of switching frequency Temp. stability of switching frequency Vi = Vcc+2VRMS; Vo = Vref; Io = 1.5A; f ripple = 100Hz Vcc = 8 to 55V Tj = 0 to 125C Vcc = 8 to 55V Vo = 3.3V; Io = 1.5A * 90 60 3 4 6 * 2 2 .5 85 100 110 * * 8 3.33 3.292 3.22 3.36 3.36 3.36 0.44 55 3.39 3.427 3.5 0.55 0.88 3 V V V V V V A % KHz dB % %
fs SV RR
3/13
L4971
Table 5. (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125C
Soft Start Soft start charge current Soft start discharge current Inhibit VLL IsLL Low level voltage Isource Low level * * 5 0. 9 15 V A 30 6 40 10 50 14 A A
DC Characteristics
Iqop Iq Iqst-by
Total operating quiescent current Quiescent current Total stand-by quiescent current Duty Cycle = 0; VFB = 3.8V Vinh <0.9V Vcc = 55V; Vinh<0.9V
4 2.5 100 150
6 3 .5 200 300
mA mA A A
Error Amplifier VFB RL Voltage Feedback Input Line regulation Ref. voltage stability vs temperature VoH VoL High level output voltage Low level output voltage Source output current Sink output current Source bias current Supply voltage ripple rejection DC open loop gain gm Transconductance Vcomp = Vfb; Vcc = 8 to 55V RL = Icomp = -0.1 to 0.1mA Vcomp = 6V 60 50 VFB = 2.5V VFB = 3.8V Vcomp = 6V; VFB = 2.5V Vcomp = 6V; VFB= 3.8V 200 200 300 300 2 80 57 2.5 3 Vcc = 8 to 55V * 10.3 0.65 3.33 3.36 5 0.4 3.39 10 V mV mV/C V V A A A dB dB ms
Io source Io sink
Ib SVRR E/A
Oscillator Section Ramp Valley Ramp peak Vcc = 8V Vcc = 55V Maximum duty cycle Maximum Frequency Duty Cycle = 0% ; Rosc = 13k, Cosc = 820pF 0.78 2 9 95 0.85 2.15 9 .6 97 300 0.92 2.3 10.2 V V V % kHz
4/13
L4971
Table 6. Typical Performance (Using Evaluation Board) fsw = 100kHz
O u tput Voltage 3.3V 5.1V 12V Output Ripple 10mV 10mV 12mV
Efficiency
VCC =35V IO = 1.5A 84 (%) 86 (%) 93 (%)
Line Regulation
Io = 1.5A VCC = 8 to 55V 3m V 3m V 3mV (VCC =15 to 55V)
Load Regulation VCC =35V IO = 0.5 to 1.5A 6mV 6mV 4mV
Figure 4. Test and valuation board circuit.
Vi=8V to 55V 5 R1 20K 3 C1 220F 63V C7 220nF C2 2.7nF 2 7 8
L4971
4 1 6 L1 126H (77120) D1 ST PS3L60U C8 330F
VO=3.3V/1.5A
R3
C5 100nF
R2 9.1K C4 22nF
C6 100nF
R4
D97IN749A
C1=220F/63V EKE C2=2.7nF C5=100nF C6=100nF C7=220nF/63V C8=330F/35V CG Sanyo L1=126H KoolMu 77120 - 65 Turns - 0.5mm R1=20K R2=9.1K D1=STPS3L60U
L4971
VO(V) 3.3 5.1 12 15 18 24 R3(K) 0 2.7 12 16 20 30 4.7 4.7 4.7 4.7 4.7 R4(K)
Figure 5. PCB and component layout of the figure 4.
5/13
L4971
Figure 6. Quiescent drain current vs. input voltage.
Iq (mA)
200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF
D97IN724
Figure 9. Line Regulation
VO (V) 3.377
Tj=125C
D97IN733
5
3.376 3.375
Tj=25C
4
3.374 3.373 3.372
3
0Hz
2
Tamb=25C 0% DC
3.371 3.370
Vcc(V)
1 0 5 10 15 20 25 30 35 40 45 50
0
5 10 15 20 25 30 35 40 45 50 VCC(V)
Figure 7. Quiescent current vs. junction temperature
Iq (mA) 5
D97IN731
Figure 10. Line Regulation
VO (V) 3.378 3.376 3.374
Tj=25C
D97IN734
VCC=35V
200KHz R1=22K C2=1.2nF 100KHz R1=20K C2=2.7nF 0Hz
4
3.372 3.370 3.368 3.366 3.364 3.362
Tj=125C
3
VCC=35V 0% DC
2
1 -50 -30 -10 10 30 50 70 90 110 Tj(C)
3.360 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 8. Stand-by drain current vs. input voltage
Ibias (A) 150 140 130 120 110 100 90 80 70 60 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Tj=125C Vss=GND Tj=25C
D97IN732
Figure 11. Switching frquency vs. R1 and C2
fsw (KHz) 500
0.8
D97IN784
Tamb=25C
200 100 50 20
2nF 1.2 nF
2.2 nF
3.3n
F 4.7n F
5.6n
F
10 5 0 20 40 60 80 R1(K)
6/13
L4971
Figure 12. Switching Frequency vs. input voltage.
fsw (KHz) 107.5 105.0 102.5 100.0 97.5 95.0 92.5 90.0 0 5 10 15 20 25 30 35 40 45 50 VCC(V)
Tj=25C
D97IN735
Figure 15. Efficiency vs output voltage.
(%) 96 94 92 90 88 86 84 82 0 5 10 15 20 25 VO(V)
VCC=35V IO=1.5A 100KHz 200KHz
D97IN737
Figure 13. Switching frequency vs. junction temperature.
fsw (KHz)
D97IN785
Figure 16. Efficiency vs. output current.
(%) 90
VCC=12V
D97IN738
VCC=8V
105
85
VCC=24V
80
100
75 70 65
90 -50 0 50 100 Tj(C)
VCC=48V fsw=100KHz VO=5.1V
95
60 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 14. Dropout voltage between pin 5 and 4
V (V) 0.5 0.4
T 2 j=
Tj=125C
D97IN736
Figure 17. Efficiency vs. output current.
(%) 90 85
VCC=12V VCC=24V VCC=8V
D97IN739
5
C
0.3 0.2 0.1
Tj=-25C
80 75 70 65
VCC=48V
fsw=100KHz VO=3.36V
0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
60
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
7/13
L4971
Figure 18. Efficiency vs. output current.
(%) 90 85 80
VCC=48V VCC=12V VCC=24V
D97IN740
Figure 21. Power dissipation vs. Vcc.
Pdiss (mW)
VO=5.1V fsw=100KHz
D97IN743
VCC=8V
800
600
IO=1.5A IO=1A
75 70 65 60
fsw=200KHz VO=5.1V
400
IO=0.5A
200
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
0
0
10
20
30
40
50 VCC(V)
Figure 19. Efficiency vs. output current.
(
D97IN741
Figure 22. Efficiency vs. VO
Pdiss (mW)
VCC=35V fsw=100KHz
D97IN744
%)
VCC=8V
90 85 80 75 70 65 60
800
VCC=12V VCC=24V
IO=1.5A
600
IO=1A
400
VCC=48V fsw=200KHz VO=3.36V
IO=0.5A
200
55 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
0
0
5
10
15
20
25
30 V0(V)
Figure 20. Efficiency vs. VCC.
(%)
V0 =5 .1V-f
SW =1
Figure 23. Pulse by pulse limiting current vs. junction temperature.
D97IN742
Ilim (A)
00KH z
D97IN747
85
V0
2.9 2.8
fsw=100KHz VCC=35V
=5
.1V
-fS
W=
20
0K
V0 =
Hz
80
3.36
V
V-f
2.7
100 KHz
0 =3
SW =
.36
V-
2.6 2.5 2.4
fS
W=
75
20
0K
IO=1.5A
Hz
70
2.3
0
10
20
30
40
50 VCC(V)
-50 -25
0
25
50
75 100 125 Tj(C)
8/13
L4971
Figure 24. Load transient. Figure 27. Soft start capacitor selection vs. Inductor and Vccmax
L (H)
D97IN746
fsw=200KHz
56nF
300
47nF
200
33nF
22nF
100
0 15 20 25 30 35 40 45 50 VCCmax(V)
Figure 25. Line transient.
VCC (V) 30 20 10 1
IO = 1A fsw = 100KHz
Figure 28. Open loop frequency and phase of error amplifier
D97IN786
GAIN (dB) 50
GAIN
D97IN787
Phase
0
0 45 90
Phase
VO (mV) 100
-50 -100
2
0 -100
1ms/DIV
-150 -200 10
135
102 103 104 105 106 107 108 f(Hz)
Figure 26. Soft start capacitor selection Vs inductor and Vccmax.
L (H)
fsw=100KHz
D97IN745
680nF 470nF
400
330nF
300
200
220nF
100
100nF
0 15 20 25 30 35 40 45 50 VCCmax(V)
9/13
L4971
Figure 29. DIP8 Mechanical Data & Package Dimensions
mm D IM . MIN. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.51 1.15 0.356 0.204 1.65 0.55 0.304 10.92 9.75 0.313 0.100 0.300 0.300 0.260 0.200 0.150 0.060 TYP. 3.32 0.020 0.045 0.014 0.008 0.065 0.022 0.012 0.430 0.384 M AX . MIN. TYP. 0.131 MAX. inch
OUTLINE AND MECHANICAL DATA
DIP-8
10/13
L4971
Figure 30. SO16 Mechanical Data & Package Dimensions
mm DIM. MIN. A A1 B C D (1) E e H h L k ddd 10.0 0.25 0.40 2.35 0.10 0.33 0.23 10.10 7.40 1.27 10.65 0.75 1.27 0.394 0.010 0.016 TYP. MAX. 2.65 0.30 0.51 0.32 10.50 7.60 MIN. 0.093 0.004 0.013 0.009 0.398 0.291 0.050 0.419 0.030 0.050 TYP. MAX. 0.104 0.012 0.200 0.013 0.413 0.299 inch
OUTLINE AND MECHANICAL DATA
0 (min.), 8 (max.) 0.10 0.004
(1) "D" dimension does not include mold flash, protusions or gate burrs. Mold flash, protusions or gate burrs shall not exceed 0.15mm per side.
SO16 (Wide)
0016021 C
11/13
L4971
4
REVISION HISTORY
Table 7. Revision History
Date October 2004 May 2005 Revision 10 11 First Issue in EDOCS Updated the Layout look & feel. Changed name of the D1 on the figs. 1 and 4. Description of Changes
12/13
L4971
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners 2005 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com
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