ST L4976 User Manual

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