ST L5973D User Manual

2.5 A switch step down switching regulator

Features

■ 2.5 A internal switch

■ Operating input voltage from 4 V to 36 V

■ 3.3 V / (±2%) reference voltage

■ Output voltage adjustable from 1.235 V to 35 V

■ Low dropout operation: 100 % duty cycle

■ 250 kHz 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

Figure 1. Test application circuit

VREF

VIN = 4.4V to 35V

C1

10µF

35V

CERAMIC

3.3V

SYNC.

COMP

C4

22nF

C3

220pF

VCC

R3

4.7K

6

8

2

4

L5973D

3

L5973D

HSOP8 exposed pad

Description

The L5973D is a step down monolithic power
switching regulator with a minimum switch current
limit of 2.5 A so it is able to deliver more than 2 A
DC current to the load depending on the
application conditions.
The output voltage can be set from 1.235 V to
35 V. The high current level is also achieved
thanks to an SO8 package with exposed frame,
that allows to reduce the Rth(j-amb) down to
approximately 40 °C/W.
The device uses an internal P-channel D-MOS
transistor (with a typical Rdson of 250 mΩ) as
switching element to minimize the size of the
external components.
An internal oscillator fixes the switching frequency
at 250 kHz.
Having a minimum input voltage of 4 V only, it is
particularly suitable for 5 V 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.

OUT

1

5

7

GNDINH

FB

L1 15µH

D1

STPS340U

R1

5.6K

R2

3.3K

VOUT=3.3V

C2

330µF

10V

D03IN1439

January 2008 Rev 16 1/17

www.st.com

17

Contents L5973D

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2/17

L5973D 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

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 1.23 V. An external resistive divider is required for higher
output voltages.

8

7

6

5

VCC

GND

VREF

FB

6 VREF 3.3 V V

7 GND Ground.

8 VCC Unregulated DC input voltage.

. No cap is requested for stability.

REF

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Electrical data L5973D

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 = 0.1 µs

Maximum output current int. limit.

Analog pins 4 V

5

INH -0.3 V to V

SYNC -0.3 to 4 V

Power dissipation at TA ≤ 60 °C 2.25 W

Operating junction temperature range -40 to 150 °C

Storage temperature range -55 to 150 °C

2.2 Thermal data

Table 3. Thermal data

Symbol Parameter

R

thJA

1. Package mounted on board

Maximum thermal resistance junction-ambient 40

-1 to 40

-5 to 40

CC

HSOP8

Exposed Pad

(1)

V
V

Unit

°C/W

4/17

L5973D Electrical characteristics

3 Electrical characteristics

Table 4. Electrical characteristics

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

Symbol Parameter Test condition Min Typ Max Unit

V

R

DS(on)

f

CC

I

s

l

Operating input
voltage range

Mosfet on
Resistance

Maximum limiting
current

Switching frequency

= 1.235 V; Io = 2 A

V

o

V

CC

Duty cycle 0 100 %

Dynamic characteristics (see test circuit ).

V

5

Voltage feedback

h Efficiency V

4.4 V < V
20 mA < I

= 5 V, VCC = 12 V 90 %

O

DC characteristics

I

qop

I

I

qst-by

q

Total operating
quiescent current

Quiescent current

Total stand-by
quiescent current

Duty Cycle = 0;
V

FB

V

inh

V

CC

V

inh

Inhibit

(1)

(1)

436V

0.250 0.5 Ω

= 4.4 V to 36 V 2.5 3 3.5 A

(1)

212 250 280 kHz

225 250 275 kHz

CC

O

= 1.5 V

> 2.2 V

= 36 V;

> 2.2 V

< 36 V,

< 2 A

1.220 1.235 1.25 V

(1)

1.198 1.235 1.272 V

(1)

(1)

(1)

35mA

50 100 µA

80 150 µA

2.5 mA

Error amplfier

V

OH

V

OL

I

o source

I

o sink

INH threshold
voltage

High level output
voltage

Low level output
voltage

Source output
current

Sink output current

Device ON 0.8 V

Device OFF 2.2 V

VFB = 1 V 3.5 V

VFB = 1.5 V 0.4 V

V

= 1.9 V;

COMP

= 1 V

V

FB

= 1.9 V;

V

COMP

VFB = 1.5 V

200 300 µA

11.5 mA

5/17

Electrical characteristics L5973D

Table 4. Electrical characteristics (continued)

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

Symbol Parameter Test condition Min Typ Max Unit

I

b

Source bias current 2.5 4 µA

DC open loop gain R

gm Transconductance

Sync function

High input voltage V

Low input voltage V

Slave sink current

Master output
amplitude

Output pulse width

Reference section

Reference voltage 3.234 3.3 3.366 V

Line regulation

Load regulation I

Short circuit current 10 18 30 mA

= ∞ 50 57 dB

L

= -0.1 mA to

I

comp

0.1 mA
= 1.9 V

V

COMP

= 4.4 V to 36 V 2.5 V

CC

= 4.4 V to 36 V 0.74 V

CC

= 0.74 V

V

sync

V

= 2.33 V

sync

= 3 mA 2.75 3 V

I

source

(2)

no load,
V

= 1.65 V

sync

I

= 0 to 5 mA

REF

= 4.4 V to 36 V

V

CC

I

= 0 mA

REF

= 4.4 V to 36 V

V

CC

= 0 to 5 mA 8 15 mV

REF

0.11

0.21

0.20 0.35 µs

(1)

3.2 3.3 3.399 V

2.3 mS

REF

0.25

0.45mAmA

510mV

V

1. Specification Referred to TJ from -40 to 125 °C. Specification over the -40 to +125 TJ Temperature range
are assured by design, characterization and statistical correlation.

2. Guaranteed by design.

6/17