Features
■ Up to 1A step down converter
■ Operating input voltage from 8v to 55v
■ Precise 5.1V reference voltage
■ Output voltage adjustable from 0.5V to 50V
■ Switching frequency adjustable up to 300kHz
■ Voltage feedforward
■ Zero load current operation
■ Internal current limiting (pulse-bypulse
■ and hiccup mode)
■ Protection against feedback disconnection
■ Thermal shutdown
Figure 1. Typical application circuit
L4976
1A step down switching regulator
DIP8 SO16W
Description
The L4976 is a step down monolithic power
switching regulator delivering 1A 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 DMOS transistor (with a typical R
obtain very high efficency and high switching
speed. 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 40V 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,
protection against feedback loop disconnection
and thermal shutdown. The device is available in
plastic dual in line, MINIDIP 8 for standard
assembly, and SO16W for SMD assembly.
ds(ON)
of 0.25Ω) to
Vi=8V to 55V
C
1
220µF
63V
C
7
220nF
R
1
20K
C
2
2.7nF
5
3
2
L4976
7
R
2
9.1K
22nF
1
C
4
6
C
6
100nF
8
4
D1
GI
SB360
L1
260µH
(77120)
C
330µF
VO=3.3V/1A
8
April 2007 Rev 7 1/17
www.st.com
17
Contents L4976
Contents
1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 Operating temperature rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 Typical charcteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/17
L4976 Block diagram
1 Block diagram
Figure 2. Block diagram
V
CC
5
VOLTAGES
MONITOR
PWM
5.1V
INTERNAL
REFERENCE
3.3V
R
Q
S
DRIVE
CBOOT
CHARGE
CBOOT
CHARGE
AT LIGHT
LOADS
6
BOOT
REF
V
COMP
FB
2
7
8
3.3V
THERMAL
SHUTDOWN
V
REF
E/A
OSCILLATOR
3
OSC GND OUT
1
4
3/17
Pin settings L4976
2 Pin settings
2.1 Pin connection
Figure 3. Pin connection (top view)
GND
REF
V
OSC
OUT
1
2
3
4 VCC
DIP8
2.2 Pin description
Table 1. Pin description
N° Pin
DIP8
1 2 GND Ground
2 3 VREF 5.1V Reference voltage with 20mA current capability.
3 4 OSC
SO16W
(1)
N.C.
FB8
COMP
7
BOOT
6
5
Name Description
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)
GND
REF
V
OSC
OUT
OUT
N.C.
N.C. N.C.
2
3
4
5
6
7
8
SO16
16
15
14
13
12
11
10
N.C.1
N.C.
FB
COMP
BOOT
VCC
N.C.
9
4 5, 6 OUT Stepdown regulator output.
5 11 VCC Unregulated DC input voltage.
6 12 BOOT
7 13 COMP E/A output to be used for frequency compensation.
8 14 FB
1. Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die.
4/17
A capacitor connected between this pin and OUT allows
to drive the internal VDMOS.
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.
L4976 Electrical data
3 Electrical data
3.1 Maximum ratings
Table 2. Absolute maximum ratings
Symbol
DIP8
V5 V11 Input voltage 58 V
V4 V5, V6
I4 I5, I6 Maximum output current internal limit
V6-V5 V12-V11 14 V
V6 V12 Bootstrap voltage 70 V
S016W
Output DC voltage -1 V
Output peak voltage at t = 0.1µs, f = 200kHz -5 V
Parameter Value Unit
V7 V13
V8 V14
Power dissipation a TA ≤ 60°C
P
TOT
T
J,TSTG
Analogs input voltage (V
(V
= 20V)
CC
Junction and storage temperature
3.2 Thermal data
Table 3. Thermal data
Symbol Parameter
R
thJA
1. Package mounted on board
Maximum thermal resistance junction-ambient
3.3 Operating temperature rating
Table 4. Operating temperature rating
Symbol Parameter
= 24V) 12 V
CC
6 V
-0.3 V
DIP8 1 W
SO16 0.8 W
-40 to 150 °C
DIP8
90
S016W Unit
(1)
110
(1)
Value
°C/W
Unit
T
J
Junction temperature range -40 to 150 °C
5/17
Electrical characteristics L4976
4 Electrical characteristics
Table 5. Electrical characteristics
(T
= 25°C, C
J
Symbol Parameter Test condition Min Typ Max Unit
Dynamic characteristic
= 2.7nF, R
OSC
= 20kΩ, VCC = 24V, unless otherwise specified.)
OSC
V
I
V
O
Operating input voltage range
Output voltage
Vd Dropout voltage
Il
Maximum limiting current
Efficiency
fs
Switching frequency
SVRR Supply voltage ripple rejection
Voltage stability of switching
frequency
Temp. stability of switching
frequency
Reference section
Reference voltage 5.0 5.1 5.2 V
Line regulation
Load regulation
Short circuit current 30 65 100 mA
VO = 3.3 to 50V; IO = 1A
IO = 0.5A
I
= 0.2 to 1A
O
+ 2V
ripple
(1)
(1)
; VO = V
RMS
= 100Hz
(1)
V
= 8 to 55V
CC
= 10V; IO = 1A
V
CC
(1)
VCC = 8 to 55V
= 3.3V; IO = 1A
V
O
(1)
VI = V
CC
= 1.A; f
I
O
= 8 to 55V
V
CC
= 0 to 125°C
T
J
I
= 0 to 10mA;
ref
V
= 8 to 55V
CC
I
= 0mA;
ref
V
= 8 to 55V
CC
V
= 0 to 5mA;
ref
V
= 0 to 20mA
CC
(1)
855V
3.33 3.36 3.39 V
3.2923.363.427 V
3.22 3.36 3.5 V
0.29 0.367 V
1.5 2 2.5 A
85 %
90 100 110 KHz
;
ref
60 dB
36%
4%
4.950 5.1 5.250 V
510
210mV
625mV
0.587 V
mV
6/17
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