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1.5A STEP DOWN SWITCHING REGULATOR
[
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 REFER-
ENCE VOLTAGE
OUTPUT VOLTAGE ADJUSTABLE FROM
1.26V TO 20V
SWITCHING FREQUENCY ADJUSTABLE UP
TO 500KHz
VOLTAGE FEEDFORWARD
ZERO LOAD CURRENT OPERATION
INTERNAL CURRENT LIMITING (PULSE-BY-
PULSE AND HICCUP MODE)
INHIBIT FOR ZERO CURRENT CONSUMP-
TION
PROTECTION AGAINST FEEDBACK DIS-
CONNECTION
THERMAL SHUTDOWN
SOFT START FUNCTION
Minidip
SO16W
ORDERING NUMBERS: L5971 (Minidip)
L5971D (SO16)
A switching frequency up to 500KHz is achiev-
able (the maximum power dissipation of the pack-
ages must be observed).
Features of this new generations of DC-DC con-
verter include pulse-by-pulse current limit, hiccup
mode for short circuit protection, voltage feedfor-
ward regulation, soft-start, protection against
feedback loop disconnection, inhibit for zero cur-
rent 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
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 technol-
ogy, the device uses an internal power D-MOS
transistor (with a typical Rdson of 0.25 W )toob-
tain very high efficency and high switching speed.
TYPICAL APPLICATION CIRCUIT
Vi=6V to 28V
5(11)
8(14)
R 1
22K
L5971
V O =2.5V/1.5A
3(4)
4(5,6)
L1
30
2(3)
7(13)
1(2)
6(12)
m
H
C 1
47m
F
30V
C 2
1.2nF
R 3
R 2
9.1K
C 6
100nF
C 5
47nF
D1
STPS
3L40U
C 8
330
m
F
C 4
22nF
R 4
D98IN832C
December 1998
1/11
11016466.002.png
L5971
BLOCK DIAGRAM
VCC
5
THERMAL
SHUTDOWN
VOLTAGES
MONITOR
CBOOT
CHARGE
2
INTERNAL
REFERENCE
INTERNAL
SUPPLY
SS_INH
INHIBIT
SOFTSTART
1.26V
5.1V
7
COMP
6
BOOT
8
E/A
FB
PWM
R
S
1.26V
Q
CBOOT
CHARGE
AT LIGHT
LOADS
DRIVE
OSCILLATOR
3
1
4
OSC
GND
OUT
D98IN833
PIN CONNECTIONS
N.C.
GND
SS_INH
OSC
OUT
1
16
N.C.
2
15
N.C.
GND
SS_INH
OSC
OUT
1
8
7
6
5
FB
3
14
13
12
11
10
9
FB
4
5
6
7
8
COMP
2
COMP
BOOT
VCC
3
BOOT
OUT
4
VCC
N.C.
N.C.
D97IN595
N.C.
N.C.
D97IN596
Minidip
SO16W
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).
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).
3
4
OSC
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)
4
5, 6
OUT
Stepdown regulator output
5
11
V CC
Not regulated DC input voltage
6
12
BOOT
A capacitor connected between this pin and OUT allows to drive the internal VDMOS
7
13
COMP
E/A output to be used for frequency compensation
8
14
FB
Stepdown feedback input. Connecting directly this pin to the output 1.26V is obtained; a
voltage divider is requested for higher output voltages
(*) Pins 1, 7, 8, 9, 10, 15 and 16 are not connected.
2/11
11016466.003.png
L5971
THERMAL DATA
Symbol
Parameter
Minidip
SO16
Unit
R th(j-amb) Thermal Resistance Junction to ambient
Max.
90 (*)
110 (*)
°
C/W
(*) Package mounted on board.
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
Minidip
S016
V 5 ,V 3
V 11 ,V 4
Input voltage
30
V
V 4
V 5 ,V 6
Output DC voltage
Output peak voltage at t = 0.1
m
s f=200KHz
-1
-5
V
V
I 4
I 5 ,I 6
Maximum output current
int. limit.
V 6 -V 5
V 12 -V 11
14
V
V 6
V 12
Bootstrap voltage
45
V
V 7 ,V 2
V 13 ,V 3
Analogs input voltage (V CC = 12V)
10
V
V 8
V 14
(V CC = 20V)
6
-0.3
V
V
P tot
Power dissipation a T amb
3
60
°
C
Minidip
1
W
SO16
0.8
W
T j ,T stg
Junction and storage temperature
-40 to 150
C
ELECTRICAL CHARACTERISTICS (Tj = 25 ° C, Cosc = 2.7nF, Rosc = 20k W ,V CC = 12V, unless other-
wise specified.) * Specification Refered to Tj from 0 to 125 ° C
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
DYNAMIC CHARACTERISTIC
V I
Operating input voltage range
*
6.5
28
V
V o
Output voltage
I o = 0.5A
1.247
1.26
1.273
V
I o = 0.2 to 1.5A
1.235
1.26
1.285
V
V cc = 6.5 to 25V
*
1.21
1.26
1.31
V
V d
Dropout voltage
V cc = 10V; I o = 1.5A
0.44
0.55
V
*
0.88
V
I l
Maximum limiting current
V cc = 6.5 to 25V
*
2
2.5
3
A
Efficiency
V o = 3.3V; I o = 1.5A
85
%
f s
Switching frequency
*
90
100
110
KHz
SVRR
Supply voltage ripple rejection V i =V cc +2V RMS ;V o =V ref ;
I o = 1.5A; f ripple = 100Hz
60
dB
Voltage stability of switching
frequency
Vcc = 6.5 to 25V
3
6
%
Temp. stability of switching
frequency
T j = 0 to 125
°
C
4
%
Soft Start
Soft start charge current
30
40
50
m
A
Soft start discharge current
6
10
14
m
A
Inhibit
V LL
Low level voltage
*
0.9
V
I sL L
Isource Low level
*
5
15
m
A
3/11
°
11016466.004.png
L5971
ELECTRICAL CHARACTERISTICS (continued)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
DC Characteristics
I qop
Total operating quiescent
current
Pin 5 (Pin 11)
3
4.5
mA
I q
Quiescent current
Duty Cycle = 0; V FB = 1.7V
2.8
3.5
mA
I qst-by
Total stand-by quiescent
current
V inh <0.9V
100
200
m
A
Vcc = 25V; V inh <0.9V
150
300
m
A
Error Amplifier
V FB
Voltage Feedback Input
1.247
1.26
1.273
V
R L
Line regulation
Vcc = 6.5 to 25V
5
10
mV
Ref. voltage stability vs
temperature
*
0.4
mV/ ° C
V oH
High level output voltage
V FB = 0.8V
8.7
V
V oL
Low level output voltage
V FB = 1.7V
0.65
V
I o source
Source output current
V comp = 3V; V FB = 0.8V
180
250
m
A
I osink
Sink output current
V comp = 3V; V FB = 1.7V
200
300
m
A
I b
Source bias current
2
3
m
A
SVRR E/A Supply voltage ripple rejection V comp =V fb ; Vcc = 6.5 to 25V
60
80
dB
DC open loop gain
R L =
8
50
57
dB
gm
Transconductance
I comp = -0.1 to 0.1mA
V comp =6V
4.3
mS
Oscillator Section
Ramp Valley
0.74
0.81
0.88
V
Ramp peak
Vcc = 6.5V
1.80
1.87
1.94
V
Vcc = 25V
4.72
4.79
4.86
V
Maximum duty cycle
95
97
%
Maximum Frequency
Duty Cycle = 0%
R osc = 13k
500
kHz
W
,C osc = 820pF
4/11
11016466.005.png
L5971
Figure 1. Test and valutation board circuit.
Vi=6V to 28V
5(11)
R 1
22K
8(14)
V O (V) R3 (K
W
)R4(K
W
)
L5971
V O =2.5V/1.5A
1.8
1
2
3(4)
4(5,6)
7(13)
1(2)
6(12)
L1
30 m H
1.5
0.5
2
2(3)
C 1
47m
2.5
2
2
C 2
1.2nF
R 3
F
30V
3.3
8.2
4.7
R 2
9.1K
C 6
100nF
D1
STPS
3L40U
C 8
330 m F
C 5
47nF
5.1
12
3.6
C 4
22nF
R 4
12
27
3
15
23
2
D98IN832C
Figure 2. PCB and component layout of the figure 1.
SOLDER SIDE
COMPONENT SIDE
5/11
11016466.001.png

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