1.5A STEP DOWN SWITCHING REGULATOR
UP TO 1.5A STEPDOWN CONVERTER
OPERATINGINPUT VOLTAGE FROM 8V TO
55V
PRECISE 3.3V (±1%) INTERNAL REFER-
ENCE VOLTAGE
OUTPUT VOLTAGE ADJUSTABLE FROM
3.3VTO 50V
SWITCHINGFREQUENCY ADJUSTABLE UP
TO 500KHz
VOLTAGEFEEDFORWARD
ZEROLOAD CURRENTOPERATION
INTERNAL CURRENT LIMITING (PULSE-BY-
PULSEAND HICCUPMODE)
INHIBIT FOR ZERO CURRENT CONSUMP-
TION
PROTECTION AGAINST FEEDBACK DIS-
CONNECTION
THERMAL SHUTDOWN
SOFTSTART FUNCTION
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 0.25Ω)toobtainvery high efficency and high switchingspeed.
TYPICAL APPLICATIONCIRCUIT
L4971
Minidip SO16W
ORDERING NUMBERS: L4971 (Minidip)
L4971D (SO16)
A switching frequency up to 500KHz 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’sapplications.
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 SO16W
for SMD assembly.
May 2000
Vi=8V to 55V
C1
220µF
63V
C7
220nF
R1
20K
C2
2.7nF
C5
100nF
5
3
2
L4971
7
R2
9.1K
22nF
1
C4
6
C6
100nF
D97IN748A
8
4
D1
GI
SB360
L1
126µ
H
(77120)
C
330µF
VO=3.3V/1.5A
8
1/12
L4971
BLOCKDIAGRAM
COMP
FB
2
7
8
3.3V
SS_INH
THERMAL
SHUTDOWN
INHIBIT SOFTSTART
E/A
OSCILLATOR
VOLTAGES
MONITOR
PWM
3.3V
INTERNAL
REFERENCE
R
Q
S
INTERNAL
SUPPLY
5.1V
DRIVE
VCC
5
CBOOT
CHARGE
CBOOT
CHARGE
AT LIGHT
LOADS
6
BOOT
3
OSC GND OUT
1
4
D97IN594
PIN CONNECTIONS
GND
SS_INH
OSC
OUT
1
2
3
4 VCC
D97IN595
FB8
COMP
7
BOOT
6
5
Minidip
N.C.
GND
SS_INH
OSC
OUT
OUT
N.C.
N.C. N.C.
2
3
4
5
6
7
8
D97IN596
16
15
14
13
12
11
10
9
SO16W
N.C.1
N.C.
FB
COMP
BOOT
VCC
N.C.
PIN FUNCTIONS
DIP SO (*) Name Function
1 2 GND Ground
2 3 SS_INH A logic signal (active low) disables the device (sleep mode operation).
3 4 OSC An external resistor connected between the unregulated input voltage and this pin and
4 5, 6 OUT Stepdown regulator output
511 V
CC Unregulated DC input voltage
6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal DMOS
7 13 COMP E/A output to be used for frequency compensation
8 14 FB Stepdown feedback input. Connecting directly to this pin results in an output voltage of
(*) Pins 1, 7,8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
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).
a capacitor connected from this pin to groundfix the switching frequency. (Linefeed
forward is automatically obtained)
Transistor
3.3V. An externalresistive divider is required for higher output voltages.
2/12
THERMALDATA
Symbol Parameter Minidip SO16 Unit
R
th(j-amb)
(*) Package mounted on board.
Thermal Resistance Junction to ambient Max. 90 (*) 110 (*) °C/W
ABSOLUTE MAXIMUM RATINGS
L4971
Symbol
Minidip S016
V
11
V5,V
I5,I
V12-V
V
12
V
13
V3 Analogs input voltage (VCC = 24V) 13 V
V
14
P
tot
V
V
5
V
4
I
4
6-V5
V
6
V
7
V
2
V
8
Input voltage 58 V
Output DC voltage
6
Output peak voltage at t = 0.1µs f=200KHz
Maximum output current int. limit.
6
11
Bootstrap voltage 70 V
Analogs input voltage (VCC= 24V) 12 V
(VCC= 20V) 6
Power dissipation a T
Parameter Value Unit
-1
-5
V
V
14 V
V
-0.3
≤ 60°C Minidip 1W
amb
V
SO16 0.8 W
T
j,Tstg
Junction and storage temperature -40 to 150 °C
ELECTRICAL CHARACTERISTICS (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ,VCC = 24V, unless other-
wisespecified.) * SpecificationReferedto Tj from 0 to 125°C
Symbol Parameter Test Condition Min. Typ. Max. Unit
DYNAMICCHARACTERISTIC
V
V
o
V
d Dropout voltage Vcc = 10V; Io = 1.5A 0.44 0.55 V
I
l Maximum limiting current Vcc = 8to 55V * 2 2.5 3 A
f
s Switching frequency * 90 100 110 KHz
SVRR Supply voltage ripple rejection V
Operating input voltage range Vo= 3.3 to 50V; Io= 1.5A * 8 55 V
I
Output voltage Io= 0.5A 3.33 3.36 3.39 V
I
= 0.2 to 1.5A 3.292 3.36 3.427 V
o
V
= 8to 55V * 3.22 3.36 3.5 V
cc
* 0.88 V
Efficiency V
Voltage stability of switching
o = 3.3V; Io = 1.5A 85 %
i =Vcc+2VRMS;Vo=Vref;
I
= 1.5A; f
o
ripple
= 100Hz
60 dB
Vcc = 8 to 55V 3 6 %
frequency
Temp. stability of switching
j = 0 to 125°C4%
T
frequency
Soft Start
Soft start charge current 30 40 50 µA
Soft start discharge current 6 10 14 µA
Inhibit
VLL Low level voltage * 0.9 V
I
sLL Isource Low level * 5 15 µA
3/12
L4971
ELECTRICAL CHARACTERISTICS (continued)
Symbol Parameter Test Condition Min. Typ. Max. Unit
DC Characteristics
Iqop Total operating quiescent
current
I
q Quiescent current Duty Cycle = 0; V
I
qst-by
Total stand-by quiescent
current
V
<0.9V 100 200 µA
inh
Vcc = 55V; V
= 3.8V 2.5 3.5 mA
FB
<0.9V 150 300 µA
inh
Error Amplifier
V
FB
R
L Line regulation Vcc = 8 to 55V 5 10 mV
V
oH High level output voltage V
V
oL Low level output voltage V
I
o source Source output current V
I
o sink Sink output current V
I
b Source bias current 2 3 µA
SVRR E/A Supply voltage ripple rejection V
gm Transconductance I
Voltage Feedback Input 3.33 3.36 3.39 V
Ref. voltage stability vs
* 0.4 mV/°C
temperature
= 2.5V 10.3 V
FB
= 3.8V 0.65 V
FB
= 6V; VFB= 2.5V 200 300 µA
comp
= 6V; VFB= 3.8V 200 300 µA
comp
; Vcc = 8 to 55V 60 80 dB
= ∞ 50 57 dB
= -0.1 to 0.1mA
=6V
DC open loop gain R
comp=Vfb
L
comp
V
comp
OscillatorSection
Ramp Valley 0.78 0.85 0.92 V
Ramp peak Vcc= 8V 2 2.15 2.3 V
Vcc = 55V 9 9.6 10.2 V
Maximum duty cycle 95 97 %
Maximum Frequency Duty Cycle = 0%
R
osc
= 13kΩ,C
= 820pF
osc
46mA
2.5 ms
500 kHz
4/12
TypicalPerformance(Using EvaluationBoard) fsw = 100kHz
L4971
Output
Voltage
Output
Ripple
Efficiency
V
CC =35V IO = 1.5A
Line Regulation
Io = 1.5A VCC = 8 to 55V
VCC =35V IO = 0.5 to 1.5A
3.3V 10mV 84 (%) 3mV 6mV
5.1V 10mV 86 (%) 3mV 6mV
12V 12mV 93 (%) 3mV (V
CC =15 to 55V) 4mV
Figure1. Testand valuation board circuit.
Vi=8V to 55V
R1
20K
C1
220µF
63V
C7
220nF
C1=220µF/63V EKE
C2=2.7nF
C5=100nF
C6=100nF
C7=220nF/63V
C8=330µF/35V CG
L1=126µH KoolMu 77120 - 65 Turns R1=20K
R2=9.1K
D1=GI SB360
C2
2.7nF
Sanyo
C5
100nF
5
3
2
22nF
0.5mm
C4
L4971
7
R2
9.1K
8
4
1
6
C6
100nF
D1
GI
SB360
D97IN749A
L4971
VO(V) R3(KΩ) R4(KΩ)
3.3
5.1
12
15
18
24
0
2.7
12
16
20
30
L1
126µH
(77120)
C
330µF
8
4.7
4.7
4.7
4.7
4.7
Load Regulation
VO=3.3V/1.5A
R
3
R
4
Figure2. PCBand componentlayout of the figure 1.
5/12
L4971
Figure3. Quiescentdraincurrent vs. input
voltage.
Iq
(mA)
200KHz
R1=22K
5
C2=1.2nF
4
3
2
Tamb=25°
C
0% DC
1
0 5 10 15 20 25 30 35 40 45 50
100KHz
R1=20K
C2=2.7nF
0Hz
D97IN724
Vcc(V)
Figure5. Stand-bydrain currentvs. input
voltage
Ibias
(µA)
150
140
Vss=GND
Tj=25°C
130
120
110
100
Tj=125°C
90
80
70
60
0 5 10 15 20 25 30 35 40 45 50 VCC(V)
D97IN732
Figure 4. Quiescent currentvs. junction
temperature
200KHz
R
=22K
1
=1.2nF
C
2
0Hz
D97IN731
Iq
(mA)
5
4
100KHz
=20K
R
1
=2.7nF
C
2
3
VCC=35V
2
0% DC
1
-50 -30 -10 10 30 50 70 90 110 Tj(°C)
Figure 6. LineRegulation
VO
(V)
3.377
Tj=125°C
3.376
3.375
3.374
3.373
3.372
3.371
3.370
0 5 10 15 20 25 30 35 40 45 50 VCC(V)
D97IN733
Tj=25°C
Figure7. Loadregulation
VO
(V)
3.378
3.376
3.374
3.372
3.370
3.368
3.366
3.364
3.362
3.360
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
6/12
Tj=125°C
V
Tj=25°C
CC
=35V
D97IN734
Figure 8. Switching frquency vs. R1 and C2
fsw
(KHz)
500
200
0.82nF
1.2nF
100
50
20
2.2nF
3.3nF
4.7nF
5.6nF
10
5
0 20 40 60 80 R1(KΩ)
D97IN784
Tamb=25°C
L4971
Figure9. SwitchingFrequencyvs.input
voltage.
fsw
(KHz)
107.5
105.0
102.5
Tj=25°C
100.0
97.5
95.0
92.5
90.0
0 5 10 15 20 25 30 35 40 45 50 VCC(V)
D97IN735
Figure11. Dropout voltage between pin 5
and 4.
∆V
(V)
0.5
0.4
0.3
0.2
0.1
D97IN736
Tj=125°C
Tj=25°C
Tj=-25°C
Figure 10. Switching frequency vs. junction
temperature.
fsw
(KHz)
105
100
95
90
-50 0 50 100 Tj(°C)
D97IN785
Figure 12. Efficiency vs output voltage.
(%)
96
94
92
90
88
86
84
η
100KHz
200KHz
V
I
O
=35V
CC
=1.5A
D97IN737
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
Figure13. Efficiencyvs. output current.
η
(%)
V
=12V
90
CC
85
V
=24V
CC
80
=48V
V
75
CC
70
65
60
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
D97IN738
VCC=8V
fsw=100KHz
VO=5.1V
82
0 5 10 15 20 25 VO(V)
Figure 14. Efficiencyvs.outputcurrent.
η
(%)
90
85
80
75
=12V
V
CC
VCC=8V
V
=24V
CC
V
=48V
CC
70
65
60
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
D97IN739
fsw=100KHz
VO=3.36V
7/12
L4971
Figure15. Efficiencyvs. output current.
η
(%)
90
85
80
=12V
V
CC
V
CC
V
=24V
CC
VCC=8V
=48V
75
70
65
60
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
D97IN740
fsw=200KHz
VO=5.1V
Figure17. Efficiencyvs. Vcc.
SW
=
1
200KHz
D97IN742
=100KHz
η
(%)
85
80
75
V
=5.1V-f
0
SW
=100KHz
V
0
=5.1V-f
SW
=200KHz
V
=3.36V-f
0
V
0
=3.36V-f
SW
IO=1.5A
Figure 16. Efficiencyvs.outputcurrent.
η
(%)
90
85
80
VCC=8V
=12V
V
CC
V
=24V
CC
75
70
V
=48V
CC
65
60
55
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 IO(A)
D97IN741
fsw=200KHz
VO=3.36V
Figure 18. Powerdissipationvs.Vcc.
Pdiss
(mW)
800
600
400
200
=5.1V
V
O
fsw=100KHz
IO=1.5A
D97IN743
I
=1A
O
=0.5A
I
O
70
0 1020304050VCC(V)
Figure19. Efficiencyvs. Vo.
Pdiss
8/12
(mW)
800
600
400
200
0
0 5 10 15 20 25 30 V0(V)
V
CC
fsw=100KHz
=35V
IO=1.5A
I
=0.5A
O
I
O
D97IN744
=1A
0
0 1020304050VCC(V)
Figure 20. Pulsebypulselimitingcurrentvs.
junction temperature.
Ilim
(A)
2.9
fsw=100KHz
VCC=35V
2.8
2.7
2.6
2.5
2.4
2.3
-50 -25 0 25 50 75 100 125Tj(°C)
D97IN747
L4971
Figure21. Load transient.
Figure23. Soft start capacitorselectionVs in-
ductor and Vccmax.
L
(µH)
400
300
200
100
680nF
fsw=100KHz
D97IN745
470nF
330nF
220nF
100nF
Figure 22. Line transient.
1A
D97IN786
V
O
(mV)
100
0
-100
V
1
2
(V)
30
20
10
CC
1ms/DIV
IO=
fsw= 100KHz
Figure 24. Softstartcapacitorselectionvs.In-
ductorandVccmax.
L
(µH)
300
200
100
fsw=200KHz
D97IN746
56nF
47nF
33nF
22nF
0
15 20 25 30 35 40 45 50 V
CCmax
(V)
Figure25. Openloopfrequencyandphaseofer-
roramplifier
GAIN
(dB)
50
0
-50
-100
-150
-200
10 10
3
2
10
5
4
10
10
GAIN
Phase
6
10
7
D97IN787
8
10
Phase
0
45
90
135
f(Hz)10
0
15 20 25 30 35 40 45 50 VCCmax(V)
9/12
L4971
DIM.
MIN. TYP. MAX. MIN. TYP. MAX.
A 3.32 0.131
a1 0.51 0.020
B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022
b1 0.204 0.304 0.008 0.012
D 10.92 0.430
E 7.95 9.75 0.313 0.384
e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300
F 6.6 0.260
I 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060
mm inch
OUTLINE AND
MECHANICAL DATA
Minidip
10/12
L4971
DIM.
MIN. TYP. MAX. MIN. TYP. MAX.
A 2.35 2.65 0.093 0.104
A1 0.1 0.3 0.004 0.012
B 0.33 0.51 0.013 0.020
C 0.23 0.32 0.009
D 10.1 10.5 0.398 0.413
E 7.4 7.6 0.291 0.299
e 1.27 0.050
H 10 10.65 0.394 0.419
h 0.25 0.75 0.010 0.030
L 0.4 1.27 0.016 0.050
K0°(min.)8° (max.)
mm inch
0.013
OUTLINE AND
MECHANICAL DATA
SO16 Wide
L
hx
45
A
B
e
K
A1
C
H
D
16
9
E
1
8
11/12
L4971
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12/12
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