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L5971
1.5A STEP DOWN SWITCHING REGULATOR
UP TO 1.5A STEP DOWN CONVERTER OPERATING INPUT VOLTAGE FROM 6.5V TO 28V PRECISE 1.26V (1%) INTERNAL REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 1.26V TO 20V SWITCHING FREQUENCY ADJUSTABLE UP TO 300KHz VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION INTERNAL CURRENT LIMITING (PULSE-BYPULSE AND HICCUP MODE) INHIBIT FOR ZERO CURRENT CONSUMPTION PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN SOFT START FUNCTION DESCRIPTION The L5971 is a step down monolithic power switching regulator delivering 1.5A at a voltage between 1.26V and 20V (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. TYPICAL APPLICATION CIRCUIT
Vi=6V to 28V R1 22K 3(4) 2(3) C2 1.2nF C5 47nF
Minidip
SO16W
ORDERING NUMBERS: L5971 (Minidip) L5971D (SO16)
A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). 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, MINIDIP 8 for standard assembly, and SO16 for SMD assembly. Typical Applications: - High efficiency step-down converter - Portable computers - Battery charger - Distributed power - PDAs and Mobile Comminicators
5(11)
8(14)
L5971
7(13)
4(5,6)
VO=2.5V/1.5A L1 30H R3
1(2) 6(12)
C1 47F 30V
R2 9.1K C4 22nF
C6 100nF
D1 STPS 3L40U
C8 330F R4
D98IN832C
August 2001
1/11
L5971
BLOCK DIAGRAM
VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE SS_INH 2 INHIBIT SOFTSTART 1.26V COMP FB 7 8 E/A INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 6 PWM BOOT
R S
1.26V
Q DRIVE
OSCILLATOR 1 GND
CBOOT CHARGE AT LIGHT LOADS
3 OSC
4 OUT
D98IN833
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.
Minidip
SO16W
PIN FUNCTIONS
DIP 1 2 SO (*) 2 3 Name GND SS_INH Function Ground 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 disables 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 Not regulated DC input voltage A capacitor connected between this pin and OUT allows to drive the internal VDMOS E/A output to be used for frequency compensation Stepdown feedback input. Connecting directly this pin to the output 1.26V is obtained; a voltage divider is requested for higher output voltages
3
4
OSC
4 5 6 7 8
5, 6 11 12 13 14
OUT VCC BOOT COMP FB
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
2/11
L5971
THERMAL DATA
Symbol Rth(j-amb) Parameter Thermal Resistance Junction to ambient Max. Minidip 90 (*) SO16 110 (*) Unit C/W
(*) Package mounted on board.
ABSOLUTE MAXIMUM RATINGS
Symbol Minidip V5, V3 V4 I4 V6-V5 V6 V7,V2 V8 Ptot Tj,Tstg S016 V11, V4 V5,V6 I5,I6 V12-V11 V12 V13,V3 V14 Bootstrap voltage Analogs input voltage (VCC = 12V) (VCC = 20V) Power dissipation a Tamb 60C Junction and storage temperature Minidip SO16 Input voltage Output DC voltage Output peak voltage at t = 0.1s f=200KHz Maximum output current Parameter Value 30 -1 -5 int. limit. 14 45 10 6 -0.3 1 0.8 -40 to 150 V V V V V W W C Unit V V V
ELECTRICAL CHARACTERISTICS (Tj = 25C, Cosc = 2.7nF, Rosc = 20k, VCC = 12V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125C
Symbol VI Vo Parameter Operating input voltage range Output voltage Test Condition * Io = 0.5A Io = 0.2 to 1.5A Vcc = 6.5 to 25V Vcc = 10V; Io = 1.5A Vcc = 6.5 to 25V Vo = 3.3V; Io = 1.5A Vi = Vcc+2VRMS; Vo = Vref; Io = 1.5A; f ripple = 100Hz Vcc = 6.5 to 25V Tj = 0 to 125C Min. 6.5 1.247 1.235 1.21 Typ. Max. 28 1.273 1.285 1.31 0.55 0.88 3 110 Unit V V V V V V A % KHz dB % %
DYNAMIC CHARACTERISTIC
1.26 1.26 1.26 0.44 2.5 85 100
* * * *
Vd Il fs SVRR
Dropout voltage Maximum limiting current Efficiency Switching frequency Supply voltage ripple rejection Voltage stability of switching frequency Temp. stability of switching frequency
2 90 60
3 4
6
Soft Start
Soft start charge current Soft start discharge current 30 6 * * 40 10 50 14 0.9 15 A A V A 3/11
Inhibit
VLL IsLL Low level voltage Isource Low level 5
L5971
ELECTRICAL CHARACTERISTICS (continued)
Symbol Parameter Total operating quiescent current Quiescent current Total stand-by quiescent current Test Condition Pin 5 (Pin 11) Duty Cycle = 0; VFB = 1.7V Vinh <0.9V Vcc = 25V; Vinh <0.9V 1.247 Vcc = 6.5 to 25V * VFB = 0.8V VFB = 1.7V Vcomp = 3V; VFB = 0.8V Vcomp = 3V; VFB = 1.7V Vcomp = Vfb; Vcc = 6.5 to 25V RL = Icomp = -0.1 to 0.1mA Vcomp = 6V 8.7 0.65 180 200 60 50 250 300 2 80 57 4.3 Min. Typ. 3 2.8 100 150 1.26 5 0.4 Max. 4.5 3.5 200 300 1.273 10 Unit mA mA A A V mV mV/C V V A A A dB dB mS
DC Characteristics
Iqop Iq Iqst-by
Error Amplifier
VFB RL Voltage Feedback Input Line regulation Ref. voltage stability vs temperature 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 Transconductance
VoH VoL Io source Io sink Ib SVRR E/A gm
3
Oscillator Section
Ramp Valley Ramp peak Maximum duty cycle Maximum Frequency Vcc = 6.5V Vcc = 25V Duty Cycle = 0% Rosc = 13k, Cosc = 820pF 0.74 1.80 4.72 95 0.81 1.87 4.79 97 0.88 1.94 4.86 300 V V V % kHz
4/11
L5971
Figure 1. Test and valutation board circuit.
Vi=6V to 28V R1 22K
5(11)
8(14)
VO (V)
VO=2.5V/1.5A L1 30H R3
R3 (K) R4 (K) 1 0.5 2 8.2 12 27 23 2 2 2 4.7 3.6 3 2
3(4) 2(3) C2 1.2nF C5 47nF
L5971
7(13)
4(5,6)
1(2) 6(12)
1.8 1.5 2.5 3.3 5.1 12 15
C1 47F 30V
R2 9.1K C4 22nF
C6 100nF
D1 STPS 3L40U
C8 330F R4
D98IN832C
Figure 2. PCB and component layout of the figure 1.
SOLDER SIDE
COMPONENT SIDE
5/11
L5971
Figure 3. Quiescent drain current vs. input voltage.
Iq (mA)
D98IN942
Figure 4. Quiescent current vs. junction temperature
Iq (mA) 5
D98IN943
VCC=20V 0% DC
5
200KHz R1=22K C2=1.2nF
4
4
200KHz; R1=22K; C2=1.2nF
100KHz; R =2 1 0K; C2=2.7n
3
3
100KHz; R1=20K C2=2.7nF 0Hz
F
0Hz
2
Tamb=25C 0% DC
2
1 0 5 10 15 20 25 Vcc(V)
1 -50 -30 -10 10 30 50 70 90 110 Tj(C)
Figure 5. Stand-by drain current vs. input voltage
Ibias (A) 150 140 130 120 110 100 90 80 70 60
Tj=125C Vss=GND
D98IN944
Figure 6. Line Regulation
VO (V) 3.377 3.376 3.375
Tj=125C
D98IN945
3.374
Tj=25C
3.373 3.372 3.371 3.370
Tj=25C
0
5
10
15
20
25 VCC(V)
0
5
10
15
20
25 VCC(V)
Figure 7. Switching frquency vs. R1 and C2
fsw (KHz) 500
0.8
Figure 8. Switching Frequency vs. input voltage.
fsw (KHz) 107.5 105.0
D98IN947
D97IN784
Tamb=25C
200 100 50 20
2nF 1.2 nF
102.5
Tj=25C
nF
2.2
100.0 97.5
4.7n F
3.3n
F
5.6n
95.0 92.5 90.0
F
10 5 0 20 40 60 80 R1(K)
0
5
10
15
20
25 VCC(V)
6/11
L5971
Figure 9. Switching frequency vs. junction temperature.
fsw (KHz)
D97IN785
Figure 10. Dropout voltage between pin 5 and 4.
V (V) 0.5
Tj=125C
D97IN736
105
0.4
Tj =2 5 C
100
0.3 0.2
Tj=-25C
95
0.1 0.0
90 -50 0 50 100 Tj(C)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 11. Efficiency vs output voltage.
(%) 96 94 92
100KHz
D98IN948
Figure 12. Efficiency vs. output current.
(%)
D98IN949
VCC=8V
200KHz
90
VCC=12V VCC=18V
90 88 86 84 82 0 5 10 15 20 25 VO(V)
VCC=20V IO=1.5A
85
80
fsw=200KHz VO=5.1V
75 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure 13. Efficiency vs output current.
(%)
D98IN950
Figure 14. Efficiency vs. output current.
(%) 90
D98IN941
90
VCC=8V
85 80
Vcc=8V Vcc=12V
85
VCC=12V VCC=18V
75 70
fsw=200KHz VO=3.36V
Vcc=18V
80
65 60
Fsw=200KHz Vo=2.5V 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Io(A)
75 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
7/11
L5971
Figure 15. Load transient.
Figure 16. Soft start capacitor selection vs. Inductor and Vccmax
L (H)
fsw=100KHz
D98IN952
160
120
680nF
80
470nF
330 nF
40
220nF
100nF
0
20
22
24
26
28 V
CCmax(V)
Figure 17. Soft start capacitor selection vs. Inductor and Vccmax
L (H)
D98IN953
Figure 18. Open loop frequency and phase of error amplifier.
GAIN (dB) 50
D97IN787
fsw=200KHz
Phase
150
GAIN
0
100
56nF
4 7nF
0 45 90
Phase
-50
33nF
-100 -150 -200 10
50
22nF
135
0 20 22 24 26 28 VCCmax(V)
102 103 104 105 106 107 108 f(Hz)
8/11
L5971
mm DIM. 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 TYP. 3.32 0.020 0.045 0.014 0.008 MAX. MIN.
inch TYP. 0.131 MAX.
OUTLINE AND MECHANICAL DATA
0.065 0.022 0.012 0.430 0.384 0.100 0.300 0.300 0.260 0.200 0.150 0.060
Minidip
9/11
L5971
mm DIM. MIN. A A1 B C D E e H h L K 10 0.25 0.4 2.35 0.1 0.33 0.23 10.1 7.4 1.27 10.65 0.75 1.27 0.394 0.010 0.016 TYP. MAX. 2.65 0.3 0.51 0.32 10.5 7.6 MIN. 0.093 0.004 0.013 0.009 0.398 0.291
inch TYP. MAX. 0.104 0.012 0.020 0.013 0.413 0.299 0.050 0.419 0.030 0.050
OUTLINE AND MECHANICAL DATA
0 (min.)8 (max.)
SO16 Wide
L
h x 45
A B e K H D A1 C
16
9
E
1
8
10/11
L5971
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. Specification 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 (c) 2001 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. http://www.st.com
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