ST L5970D User Manual

Up to 1A step down switching regulator

Features

■ Up to 1A output current

■ Operating input voltage from 4.4V to 36V

■ 3.3V / (±2%) reference voltage

■ Output voltage adjustable from 1.2V to 35V

■ Low dropout operation: 100% duty cycle

■ 250KHz Internally fixed frequency

■ Voltage feedforward

■ Zero load current operation

■ Internal current limiting

■ Inhibit for zero current consumption

■ Synchronization

■ Protection against feedback disconnection

■ Thermal shutdown

Applications

■ Consumer: STB, DVD, TV, VCR, car radio,

LCD monitors

■ Networking: XDSL, modems, DC-DC modules

■ Computer: printers, audio/graphic cards,

optical storage, hard disk drive

■ Industrial: changers, car battery, DC-DC

converters

L5970D

SO8

Description

The L5970D is a step down monolithic power
switching regulator capable to deliver up to 1A at
output voltages from 1.2V to 35V.

The device uses an internal P-Channel D-MOS
transistor (with a typical Rdson of 250mΩ) as
switching element to minimize the size of the
external components.

An internal oscillator fixes the switching frequency
at 250KHz.

Having a minimum input voltage of 4.4V only, it is
particularly suitable for 5V bus, available in all
computer related applications.

Pulse by pulse current limit with the internal
frequency modulation offers an effective constant
current short circuit protection.

Figure 1. Test application circuit

VIN = 4.4V to 35V

C1

10µF

35V

CERAMIC

3.3V

C4

22nF

C3

220pF

VREF

VCC

SYNC.

COMP

4.7K

R3

6

8

2

4

INH.

L5970D

3

7

1

5

GND

D98IN954C

OUT

FB

L1 33µH

D1

STPS2L40U

R1

5.6K

R2

3.3K

VOUT=3.3V

C2

100µF

10V

October 2007 Rev 16 1/16

www.st.com

16

Contents L5970D

Contents

1 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2/16

L5970D Pin settings

1 Pin settings

1.1 Pin connection

Figure 2. Pin connection (top view)

COMP

1.2 Pin description

Table 1. Pin description

N° Type Description

1 OUT Regulator output.

2 SYNC Master/slave synchronization.

3INH

4 COMP E/A output for frequency compensation.

5FB

6VREF

7 GND Ground.

8 VCC Unregulated DC input voltage.

OUT

SYNC

INH

1

2

3

4

D98IN955

A logical signal (active high) disables the device. If INH not used the pin
must be grounded. When it is open an internal pull-up disable the
device.

Feedback input. Connecting directly to this pin results in an output
voltage of 1.23V. An external resistive divider is required for higher
output voltages.

3.3V V

. No cap is requested for stability.

REF

8

7

6

5

VCC

GND

VREF

FB

3/16

Electrical data L5970D

2 Electrical data

2.1 Maximum ratings

Table 2. Absolute maximum ratings

Symbol Parameter Value Unit

V

8

V

1

I

1

V

, V

4

V

3

V

2

P

TOT

T

J

T

STG

Input voltage 40 V

Output DC voltage
Output peak voltage at t = 0.1µs

-1 to 40

-5 to 40

Maximum output current int. limit.

Analog pins 4 V

5

INH -0.3V to V

SYNC -0.3 to 4 V

Power dissipation at TA ≤ 60°C 0.75 W

Operating junction temperature range -40 to 150 °C

Storage temperature range -55 to 150 °C

V
V

CC

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter SO8 Unit

R

thJA

1. Package mounted on board

Maximum thermal resistance junction-ambient

120

(1)

°C/W

4/16

L5970D Electrical characteristics

3 Electrical characteristics

Table 4. Electrical characteristics

( TJ = 25°C, VCC = 12V, unless otherwise specified)

Symbol Parameter Test condition Min Typ Max Unit

V

CC

Operating input
voltage range

Vo = 1.235V; Io = 2A

(1)

4.4 36 V

R

DS(on)

I

l

f

s

Mosfet on
Resistance

Maximum limiting
current

Switching frequency

VCC = 4.4V to 36V

Duty cycle 0 100 %

Dynamic characteristics (see test circuit ).

V

5

Voltage feedback

h Efficiency

4.4V < V
20mA < I

VO = 5V, VCC = 12V

DC characteristics

I

qop

I

I

qst-by

q

Total operating
quiescent current

Quiescent current

Total stand-by
quiescent current

Duty cycle = 0;
VFB = 1.5V

V

inh

VCC = 36V;
V

inh

CC

> 2.2V

> 2.2V

< 36V,

< 2A

O

(1)

0.250 0.5 Ω

1.5 1.87 2.25 A

(1)

212 250 280 KHz

225 250 275 KHz

1.220 1.235 1.25 V

(1)

1.198 1.235 1.272 V

90 %

(1)

(1)

(1)

35mA

50 100 µA

80 150 µA

2.5 mA

Inhibit

Error amplfier

V

OH

V

OL

I

o source

INH threshold
voltage

High level output
voltage

Low level output
voltage

Source output
current

Device ON 0.8 V

Device OFF 2.2 V

V

= 1V

FB

VFB = 1.5V

V

= 1.9V;

COMP

= 1V

V

FB

3.5 V

0.4 V

200 300 µA

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