L296.PDF

L296

L296P

. 4 A OUTPUT CURRENT

HIGH CURRENT SWITCHING REGULATORS

. 5.1 V TO 40 V OUTPUT VOLTAGE RANGE

. SWITCHING FREQUENCY UP TO 200 KHz

. VERY HIGH EFFICIENCY (UP TO 90 %)

. VERY FEW EXTERNAL COMPONENTS

. SOFT START

. RESET OUTPUT

. EXTERNAL PROGRAMMABLE LIMITING

Multiwatt )

(15 lead)

. CONTROL CIRCUIT FOR CROWBAR SCR

. INPUT FOR REMOTE INHIBIT AND

SYNCHRONUS PWM

CURRENT (L296P)

. THERMAL SHUTDOWN

ORDERING NUMBERS :

L296 (Vertical)

L296HT (Horizontal)

L296P (Vertical)

L296PHT (Horizontal)

DESCRIPTION

The L296 and L296P are stepdown power switching

regulators delivering 4 A at a voltage variable from

5.1 V to 40 V.

Features of the devices include soft start, remote in-

hibit, thermal protection, a reset output for micro-

processors and a PWM comparator input for syn-

chronization in multichip configurations.

The L296P incudes external programmable limiting

current.

The L296 and L296P are mounted in a 15-lead Mul-

tiwatt ) plastic power package and requires very few

external components.

Efficient operation at switching frequencies up to

200 KHz allows a reduction in the size and cost of

external filter components. A voltage sense input

and SCR drive output are provided for optional

crowbar overvoltage protection with an external

SCR.

PIN CONNECTION (top view)

April 1993

1/21

. 0 TO 100 % DUTY CYCLE RANGE

. PRECISE ( ± 2 %) ON-CHIP REFERENCE

L296 - L296P

PIN FUNCTIONS

Name

Function

CROWBAR INPUT Voltage Sense Input for Crowbar Overvoltage Protection. Normally connected to the

feedback input thus triggering the SCR when V out exceeds nominal by 20 %. May

also monitor the input and a voltage divider can be added to increase the threshold.

Connected to ground when SCR not used.

OUTPUT

Regulator Output

SUPPLY VOLTAGE Unrergulated Voltage Input. An internal Regulator Powers the L296s Internal Logic.

CURRENT LIMIT

A resistor connected between this terminal and ground sets the current limiter

threshold. If this terminal is left unconnected the threshold is internally set (see

electrical characteristics).

SOFT START

Soft Start Time Constant. A capacitor is connected between this terminal and ground

to define the soft start time constant. This capacitor also determines the average

short circuit output current.

INHIBIT INPUT

TTL – Level Remote Inhibit. A logic high level on this input disables the device.

SYNC INPUT

Multiple L296s are synchronized by connecting the pin 7 inputs together and omitting

the oscillator RC network on all but one device.

GROUND

Common Ground Terminal

A series RC network connected between this terminal and ground determines the

regulation loop gain characteristics.

10 FEEDBACK INPUT The Feedback Terminal on the Regulation Loop. The output is connected directly to

this terminal for 5.1V operation ; it is connected via a divider for higher voltages.

11 OSCILLATOR A parallel RC networki connected to this terminal determines the switching frequency.

This pin must be connected to pin 7 input when the internal oscillator is used.

12 RESET INPUT Input of the Reset Circuit. The threshold is roughly 5 V. It may be connected to the

feedback point or via a divider to the input.

13 RESET DELAY A capacitor connected between this terminal and ground determines the reset signal

delay time.

14 RESET OUTPUT Open collector reset signal output. This output is high when the supply is safe.

15 CROWBAR OUTPUT SCR gate drive output of the crowbar circuit.

FREQUENCY

COMPENSATION

BLOCK DIAGRAM

2/21

L296 - L296P

CIRCUIT OPERATION

(refer to the block diagram)

The L296 and L296P are monolithic stepdown

switching regulators providing output voltages from

5.1V to 40V and delivering 4A.

The regulation loop consists of a sawtooth oscillator,

error amplifier, comparator and the output stage. An

error signal is produced by comparing the output

voltage with a precise 5.1V on-chip reference (zener

zap trimmed to ± 2 %). This error signal is then com-

pared with the sawtooth signal to generate the fixed

frequencypulse width modulatedpulses which drive

the output stage. The gain and frequency stability of

the loop can be adjusted by an external RC network

connectedto pin 9. Closing the loop directly gives an

output voltage of 5.1V. Higher voltages are obtained

by inserting a voltage divider.

Output overcurrents at switch on are prevented by

the soft start function. The error amplifier output is

initially clamped by the external capacitor Css and

allowed to rise, linearly, as this capacitor is charged

by a constant current source.

Output overload protection is provided in the form of

a current limiter. The load current is sensed by an

internal metal resistor connected to a comparator.

When the load current exceeds a preset threshold

this comparator sets a flip flop which disables the

output stage and discharges the soft start capacitor.

A second comparator resets the flip flop when the

voltage across the soft start capacitor has fallen to

0.4V. The output stage is thus re-enabled and the

output voltage rises under control of the soft start

network. If the overload condition is still present the

limiter will trigger again when the threshold current

is reached. The average short circuit current is lim-

ited to a safe value by the dead time introduced by

the soft start network.

The reset circuit generates an output signal when

the supply voltage exceeds a threshold pro-

grammed by an external divider. The reset signal is

generated with a delay time programmed by an ex-

ternal capacitor. When the supply falls below the

threshold the reset output goes low immediately.

The reset output is an open collector.

The scrowbar circuit senses the output voltage and

the crowbar output can provide a current of 100mA

to switch on an external SCR. This SCR is triggered

when the output voltage exceeds the nominal by

20%. There is no internal connection between the

output and crowbar sense input therefore the crow-

bar can monitor either the input or the output.

A TTL - level inhibit input is provided for applications

such as remote on/off control. This input is activated

by high logic level and disables circuit operation. Af-

ter an inhibit the L296 restarts under control of the

soft start network.

The thermal overload circuit disables circuit opera-

tion when the junction temperature reaches about

150 ° C and has hysteresis to prevent unstable con-

ditions.

Figure 1 : Reset Output Waveforms

3/21

L296 - L296P

Figure 2 : Soft Start Waveforms

Figure 3 : Current Limiter Waveforms

ABSOLUTE MAXIMUM RATINGS

Symbol

Parameter

Value

Unit

V i

Input Voltage (pin 3)

V i –V 2

Input to Output Voltage Difference

V 2

Output DC Voltage

Output Peak Voltage at t = 0.1

sec f = 200KHz

–1

–7

V 1 ,V 12

Voltage at Pins 1, 12

V 15

Voltage at Pin 15

V 4 ,V 5 ,V 7 ,V 9 ,V 13 Voltage at Pins 4, 5, 7, 9 and 13

5.5

V 10 ,V 6

Voltage at Pins 10 and 6

V 14

Voltage at Pin 14 (I 14

1 mA)

V i

I 9

Pin 9 Sink Current

I 11

Pin 11 Source Current

I 14

Pin 14 Sink Current (V 14 < 5 V)

P tot

Power Dissipation at T case

T j ,T stg

Junction and Storage Temperature

– 40 to 150

4/21

L296 - L296P

THERMAL DATA

Symbol

Parameter

Value

Unit

R th j-case

Thermal Resistance Junction-case

Max.

C/W

R th j-amb

Thermal Resistance Junction-ambient

Max.

C/W

ELECTRICAL CHARACTERISTICS

(refer to the test circuits T j =25 o C, V i = 35V, unless otherwise specified)

Symbol

Parameter

Test Conditions

Min. Typ. Max. Unit Fig.

DYNAMIC CHARACTERISTICS (pin 6 to GND unless otherwise specified)

V o

Output Voltage Range

V i = 46V, I o =1A

V ref

V i

Input Voltage Range

V o =V ref to 36V, I o

V i

Input Voltage Range

Note (1), V o =V REF to 36V I o =4A

V o

Line Regulation

V i =10V to 40V, V o =V ref ,I o =2A

15 50

V o

Load Regulation

V o =V ref

I o =2Ato4A

I o = 0.5A to 4A

V ref

Internal Reference Voltage (pin 10) V i = 9V to 46V, I o = 2A

5.1 5.2

V ref

D T

Average Temperature Coefficient

of Reference Voltage

T j =0

C to 125

C, I o = 2A

0.4

mV/

V d

Dropout Voltage Between Pin 2

and Pin 3

I o =4A

I o =2A

1.3

3.2

2.1

I 2L

Current Limiting Threshold (pin 2) L296 - Pin 4 Open,

V i = 9V to 40V, V o =V ref to 36V

4.5

7.5

L296P - V i = 9V to 40V, V o =V ref

Pin 4 Open

R Iim = 22k

2.5

4.5

I SH

Input Average Current

V i = 46V, Output Short-circuited

100

Efficiency

I o =3A

V o =V ref

V o = 12V

SVR

Supply Voltage Ripple Rejection

V i =2V rms ,f ripple = 100Hz

V o =V ref ,I o =2A

Switching Frequency

85 100 115

kHz

Voltage Stability of Switching

Frequency

V i = 9V to 46V

0.5

V i

Temperature Stability of Switching

Frequency

T j =0

C to 125

T j

f max

Maximum Operating Switching

Frequency

V o =V ref ,I o = 1A

200

kHz

–

T sd

Thermal Shutdown Junction

Temperature

Note (2)

135 145

C–

DC CHARACTERISTICS

I 3Q

Quiescent Drain Current

V i = 46V, V 7 = 0V, S1 : B, S2 : B

V 6 =0V

V 6 =3V

–I 2L

Output Leakage Current

V i = 46V, V 6 = 3V, S1 : B, S2 : A,

V 7 =0V

Note

(1) : Using min. 7 A schottky diode.

(2) : Guaranteed by design, not 100 % tested in production.

5/21

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