ST L4973 User Manual

Features

■ Up to 3.5 A step down converter

■ Operating input voltage from 8 V to 55 V

■ 3.3 V and 5.1 V (±1%) fixed output, and

adjustable outputs from: – 0.5 V to 50 V (3.3 type) – 5.1 V to 50 V (5.1 type)

■ Frequency adjustable up to 300 kHz

■ Voltage feed forward

■ Zero load current operation (min. 1 mA)

■ Internal current limiting (pulse by pulse and

HICCUP mode)

■ Precise 5.1 V (1.5%) reference voltage

externally available

■ Input/output synchronization function

■ Inhibit for zero current consumption (100 mA

typ. at V

■ Protection against feedback disconnection

■ Thermal shutdown

■ Output over voltage protection

■ Soft-start function

Figure 1. Internal schematic diagram

= 24 V)

CC

VCC (8V to 55V)

C

IN

7

R

OSC

C2

1 4,5,6,10

13,14,15

L4973

3.5 A step down switching regulator

DIP-18 (12+3+3) SO-20 (12+4+4)

Description

The L4973 is a step down monolithic power switching regulator delivering 3.5 A at fixed voltages of 3.3 V or 5.1 V and using a simple external divider output adjustable voltage up to 50V. Realized in BCD mixed technology, the device uses an internal power D-MOS transistor (with a typical R high efficiency and very fast switching times. Switching frequency up to 300 kHz are achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8 V to 55 V and output voltages regulated from 3.3 V to 40 V cover the majority of the today applications. Features of this new generation of DC-DC converter includes pulse by pulse current limit, hiccup mode for output short circuit protection, voltage feed forward regulation, soft-start, input/output synchronization, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. Packages available are in plastic dual in line, DIP18 (12+3+3) for standard assembly, and SO20 (12+4+4) for SMD assembly.

C

8

L4973

16

12

BOOT

9

3

2

11

17

of 0.15 Ω) to obtain very

DS(on)

VO(3.3V or 5.1V)

L1

R

C

OSC

D97IN554A

COMP

C

SS

C

COMP

D1

C

OUT

February 2009 Rev 18 1/28

www.st.com

28

Contents L4973

Contents

1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8 Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

9 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

10 Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2/28

L4973 Block diagram

(x)

1 Block diagram

Figure 2. Block diagram

INH

ZERO CURRENT

INHIBIT

VREF

GOOD

5.1V

3.3V

V5.1

INTERNAL

REFERENCE

INTERNAL

SUPPLY

V

CC

5.1V

V

CC

8(9)7(8)16(18)10(11)

CBOOT

CHARGE

SS

COMP

VFB

SYNC

17(19)

11(12)

5.1V +

3.3V

E/A

-

12(13)

18(20)

Pin x = Powerdip

= S020

SOFT

START

THERMAL

SHUTDOWN

-

PWM

+

OSCILLATOR

1(1) 2(2) 3(3)

2 Pin settings

2.1 Pin connection

Figure 3. Pin connection (top view)

HICCUP CURRENT

LIMITING

CURRENT

LIMITING

R

SQQ

4,5,6,13,14,15

(4,5,6,7,14,15,16,17)

DRIVER

BOOT

9(10)

OUTOUTGNDOSC

D94IN161B

OSC

OUT

GND

V

CC

V

CC

BOOT

1

2

3

4

5

6

7

8

9 INH

D94IN162A

17

16

15

14

13

12

11

10

SYNC18

SS

V5.1

GND

VFB

COMP

OSC

OUT

GND

V

CC

V

CC

BOOT INH

2

3

4

5

6

7

8

9

10

D94IN163A

DIP -18 (12+3+3) SO20 (12+4+4)

3/28

20

19

18

17

16

15

14

13

12

11

SYNC1

SS

V5.1

GND

VFB

COMP

Pin settings L4973

2.2 Pin description

Table 1. Pin description

N° Pin

Name Description

DIP-18 SO-20

11 12 COMP E/A output to be used for frequency compensation

A logic signal (active high) disables the device (sleep

10 11 INH

mode operation). If not used it must be connected to GND; if floating the device is disabled.

9 10 BOOT

18 20 SYNC Input/Output synchronization.

7,8 8,9 V

2,3 2,3 OUT Stepdown regulator output.

12 13 VFB

16 18 V5.1 Reference voltage externally available.

4,5,6

13,14,15

1 1 OSC

4,5,6,7

14,15,16,17

CC

GND Signal ground

A capacitor connected between this pin and the output allows to drive the internal D-MOS.

Unregulated DC input voltage

Stepdown feedback input. Connecting the output directly to this pin results in an output voltage of 3.3 V for the L4973V3.3 and 5.1 V for L4973V5.1. An external resistive divider is required for higher output voltages. For output voltage resistive divider is required for higher output voltages. For output voltage less than 3.3 V, see

Note: 1 and Figure 33.

An external resistor connected between the unregulated input voltage and Pin 1 and a capacitor connected from Pin 1 to ground fixes the switching frequency. (Line feed forward is automatically obtained)

Note: 1 The maximum power dissipation of the package must be observed.

4/28

L4973 Electrical data

3 Electrical data

3.1 Maximum ratings

Table 2. Absolute maximum ratings

Symbol

Parameter Value Unit

DIP-18 S0-20

V

I

V

7,V8

2,V3

2,I3

9-V8

V

V2,V

I

Input voltage 58 V

9,V8

Output DC voltage

3

Output peak voltage at t = 0.1 μs f = 200 kHz

Maximum output current int. limit.

2,I3

V10-V8 14 V

11

17

12

18

10

V

9

V

Bootstrap voltage 70 V

10

Analogs input voltage (V

12

Analogs input voltage (VCC = 24 V) 13 V

19

(VCC = 20 V)

13

(VCC = 20 V)

20

Inhibit

11

= 24 V) 12 V

CC

-0.3

V

-0.3

DIP 12+3+3 Power dissipation a Tpins ≤ 90 °C

= 70 °C no copper area)

(T

P

tot

A

= 70 °C 4 cm copper area on PCB)

(T

A

SO-20

= 90 °C

pins

TJ,T

STG

Power dissipation a T

Junction and storage temperature -40 to 150 °C

-1

- 5

6

V V

5.5

0.3

CC

V V

5

1.3 2

W W W

4W

3.2 Thermal data

Table 3. Thermal data

Symbol Parameter DIP-18 SO-20 Unit

R

thJP

R

thJA

1. Package mounted on board

Maximum thermal resistance junction-pin 12 15 °C/W

Maximum thermal resistance junction-ambient 60

(1)

80

(1)

°C/W

5/28

Electrical characteristics L4973

4 Electrical characteristics

Table 4. Electrical characteristics

(Refer to the test circuit,V R

= 20 kΩ; unless otherwise specified)

OSC

Symbol Parameter Test condition Min Typ Max Unit

Dynamic characteristics

Input voltage range

Output voltage L4973V5.1

Output voltage L4973V3.3

(1)

VO = V

I

I to 55 V

I

I to 40 V

= 1 A 5.05 5.1 5.15 V

O

= 0.5 A to 3.5 A VCC = 8 V

O

= 1 A 3.326 3.36 3.393 V

O

= 0.5 A to 3.5 A VCC = 8 V

O

= 24 V; TJ = 25 °C, C

CC

to 40 V; IO = 3.5A

REF

= 2.7 nF;

OSC

(2)

855V

5.00 5.1 5.20 V

(2)

4.95 5.1 5.25 V

3.292 3.36 3.427 V

(2)

3.26 3.36 3.46 V

R

DS(on

)

Maximum limiting current

η Efficiency

Switching frequency

Supply voltage ripple rejection

Switching frequency

Δf

stability vs., supply

s

w

voltage

Reference section

Reference voltage

Line regulation

Load regulation

VCC = 10.5 V IO = 3.5 A

= 8 V to 55 V

V

CC

V

= 5.1 V; IO = 3.5 A 90 %

O

= 3.3 V; IO = 3.5 A 85 %

V

O

= VCC+2 V

V

i

= 1 A; f

I

O

V

CC

I

ref

ripple

= 8 V to 55 V 2 5 %

= 0 to 20 mA;

RMS VO

= 100 Hz

= V

VCC = 8 to 55 V

I

= 0 mA;

ref

VCC = 8 to 55 V

V

= 0 to 5 mA;

ref

VCC = 0 to 20 mA

ref

(2)

0.35 Ω

(2)

3.8 4.5 5.5 A

4 4.5 5.5 A

(2)

90 100 110 kHz

;

60 dB

5.025 5.1 5.175 V

(2)

4.950 5.1 5.250 V

5 10 mV

2

1025mV

6

0.15 0.22 Ω

mV

Short circuit current 30 65 100 mA

6/28

L4973 Electrical characteristics

Table 4. Electrical characteristics (continued)

(Refer to the test circuit,V R

= 20 kΩ; unless otherwise specified)

OSC

Symbol Parameter Test condition Min Typ Max Unit

Soft-start

Soft-start charge current 30 45 60 μA

= 24 V; TJ = 25 °C, C

CC

= 2.7 nF;

OSC

Soft-start discharge current

Inhibit

High level voltage

Low level voltage

high level V

I

source

I

low level V

source

DC characteristics

Total operating quiescent current

Quiescent current Duty cycle = 0 2.7 4 mA

Total stand-by quiescent current

Error amplifier

High level output voltage 11.0 V

Low level output voltage 0.65 V

Source bias current 1 2 3 μA

Source output current 200 300 600 μA

Sink output current 200 300 μA

15 22 30 μA

(2)

3.0 V

= 3 V

INH

= 0.8 V

INH

(2)

10 16 50 μA

(2)

10 15 50 μA

0.8 V

Duty cycle = 50 % 4 6 mA

V

CC

V

CC

= 24 V; V

= 55 V; V

= 5 V 100 200 μA

INH

= 5 V 150 300 μA

INH

Supply voltage ripple rejection

DC open loop gain R

Transconductance

Oscillator section

Ramp valley 0.78 0.85 0.92 V

Ramp peak

Maximum duty cycle 95 97 %

= VFB

V

COMP

C

= 4.7 μF 1-5 mA load

REF

60 80 dB

current

= ∞ 50 60 dB

L

I

= -0.1 to 0.1 mA;

comp

= 6 V

V

comp

V

= 8 V

CC

VCC = 55 V

1.992.1

2.5 mS

2.3

9.6

10.2VV

7/28

Electrical characteristics L4973

Table 4. Electrical characteristics (continued)

(Refer to the test circuit,V R

= 20 kΩ; unless otherwise specified)

OSC

Symbol Parameter Test condition Min Typ Max Unit

= 24 V; TJ = 25 °C, C

CC

= 2.7 nF;

OSC

Maximum frequency

Sync function

High input voltage VCC = 8 V to 55 V 3.5 V

Low input voltage V

Slave sink current 0.15 0.25 0.45 mA

Master output amplitude I

Output pulse width No load, V

1. Pulse testing with a low duty cycle

2. Specifications referred to T

from -40 °C to 125 °C.

J

Duty cycle = 0%; R

=13 kΩ; C

OSC

= 8 V to 55 V 0.9 V

CC

= 3 mA 4 4.5 V

source

sync

= 820 pF;

OSC

= 4.5 V 0.20 0.35 μs

300 kHz

8/28

L4973 Evaluation board

5 Evaluation board

Figure 4. Evaluation board circuit

SYNCHSYNCH

U1

OSC

SS

V5.1

L4973 DIP 18

R5NMR5 NM

3

8

VCC7VCC

JP1JP1

2

10

INH

COMP

11

C4 22nC422n

C5

R2

150pC5150p

15kR215k

VinVin

470u 63v

GNDGND

R1 15kR115k

C10

C9

220nC9220n

C2

C1

470nC2470n

2.7nC12.7n

1

17

16

C3A1uC3A

C3NMC3

1u

NM

Table 5. Component list (fsw = 150 kHz, V

18

SYNC

R6 NMR6 NM

1

C8 220nC8 220n

9

2

OUT

3

BOOT

OUT

15

GND GND GND GND GND GND

VFB

12

signal GND

GND plane

14 13 6 5 4

OUT

Q2NMQ2

NM

signal GND

= 5 V)

L1 68uHL1 68uH

R7NMR7

NM

D1 STPS5L60D1STPS5L60

1 2

C6NMC6

NM

C11

C7NMC7 NM

150u 50v

C12

C12 150u 50v

150u 50v

VoutVout

R3

2.7kR32.7k C14NMC14

NM

C13NMC13 NM

R4

4.99kR44.99k

GNDGND

Reference Description Part number Manufacturer

R1 Resistor 15 kΩ 1%

R2 Resistor 15 kΩ 1%

R3 Resistor 2.7 kΩ 1%

R4 Resistor 4.99 kΩ 1%

R5 Not mounted

R6 Not mounted

R7 Not mounted

C1 Capacitor 2.7 nF 5%

C2 Capacitor 470 nF 5%

C3 Capacitor 1 μF 5%

C4 Capacitor 22 nF 5%

C5 Capacitor 150 pF 5%

C6 Not mounted

C7 Not mounted

C8 Capacitor 220 nF 5%

C9 Capacitor 220 nF 5%

C10 Capacitor 470 μF 63V EKY-630ELL471ML20S Nippon Chemi-con

9/28