L4937N

DUAL MULTIFUNCTION VOLTAGE REGULATOR

STANDBYOUTPUT VOLTAGEPRECISION 5V

OUTPUT 2 TRACKED TO THE STANDBY OUT-
PUT

OUTPUT

DISABLE

FUNCTION

FOR

STANDBY MODE

VERY LOW QUIESCENT CURRENT, LESS
THAN 250

A, IN STANDBY MODE

OUTPUT CURRENTS : I

= 50mA, I

= 500mA

VERY LOW DROPOUT (max 0.4V/0.6V)

OPERATING TRANSIENT SUPPLY VOLTAGE
UP TO 40V

POWER-ON RESET CIRCUIT SENSING THE
STANDBY OUTPUT VOLTAGE

POWER-ON RESET DELAY PULSE DEFINED
BY THE EXTERNAL CAPACITOR

THERMAL SHUTDOWN AND SHORT CIRCUIT
PROTECTIONS

Heptawatt

ORDERING NUMBER : L4937N

DESCRIPTION

The L4937N is a monolithic integrated dual voltage
regulatorswith two very low dropout outputsand ad-
ditional functions such as power-on reset and input
voltage sense. It is designed for supplying micro-
computer controlled systems specially in automo-
tive applications.

PIN CONNECTION (top view)

June 2000

1/9

ABSOLUTE MAXIMUM RATINGS

Symbol

Parameter

Value

Unit

DC Supply Voltage

Transient Supply Voltage (T < 1s)

, T

stg

Junction and Storage Temperature Range

55 to 150

Enable Input Current (V

0.3V)

Enable Input Voltage

RES

Reset Output Voltage

RES

Reset Output Current

Power Dissipation (T

= 80

C, R

th heatsink

= 9

C/W)

Note : The circuit is ESD protected according to MILSTD883C.

APPLICATION CIRCUIT

F ; C

F, ESR < 10

at 10KHz

L4937N

3/9

ELECTRICAL CHARACTERISTICS (V

= 14V; 40

125

C unless otherwise specified)

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

Operating Supply Voltage

Standby Output Voltage

25V

1mA

50mA

4.90

5.00

5.10

- V

Output Voltage 2 Tracking Error
(note 1)

25V

5mA

500mA

Enable = LOW

+25

DP1

Dropout Voltage 1

= 10mA

= 50mA

0.1
0.2

0.25

0.4

V
V

IO1

Input to Output Voltage
Difference in Undervoltage
Condition

VS = 4V, I

= 35mA

0.4

DP2

Dropout Voltage 2

IO2 = 100mA
I

= 500mA

0.2
0.3

0.3
0.6

V
V

IO2

Input to Output Voltage
Difference in Undervoltage
Condition

VS = 4.6V, I

= 350mA

0.6

OL 1.2

Line Regulation

25V

= 1mA; I

= 5mA

OLO1

Load Regulation 1

1mA

50mA

OLO2

Load Regulation 2

5mA

500mA

LIM1

Current Limit 1

= 4.5V

= 0V (note 2)

55
25

100

200
100

mA
mA

LIM2

Current Limit 2

VO2 = 0V

550

1000

1700

QSB

Quiescent Current Standby
Mode (output 2 disabled)

= 0.3mA; T

< 100

2.4V

= 14V

= 3.5V

210
340

290
850

Quiescent Current

= 50mA

= 500mA

ENABLE

ENL

Enable Input LOW Voltage
(output 2 active)

0.3

1.5

ENH

Enable Input HIGH Voltage

2.4

ENhyst

Enable Hysteresis

200

Enable Input Current

0V < V

< 1.2V

2.5V < V

< 7V

1.5

0.5

L4937N

4/9

ELECTRICAL CHARACTERISTICS (continued)

RESET

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

Reset Low Threshold Voltage

= 14V

-0.4

4.7

-0.1

Rth

Reset Threshold Hysteresis

100

200

Reset Pulse Delay

= 100nF; t

> 100

100

180

Reset Reaction Time

= 100nF

Reset Output LOW Voltage

RES

= 10K

to V

1.5V

0.4

LRES

Reset Output HIGH Leakage

RES

= 5V

CTth

Delay Comparator Threshold

2.0

CTth, hyst

Delay Comparator Threshold
Hysteresis

100

Note :

1 : V

connected to ADJ.V

can be set to higher values by inserting an external resistor divider.

2 : Foldback characteristic

FUNCTIONAL DESCRIPTION

The L4937N is based on the SGS-THOMSON Mi-
croelectronics modular voltage regulator approach.
Several out-standing features and auxiliary func-
tions are provided to meet the requirements of sup-
plying the microprocessor systems used in automo-
tive applications.

Furthermore the device is suitable also in other ap-
plications requiring two stabilized voltages.

The modular approach allows other features and
functions to be realized easily when required.

STANDBY REGULATOR

The standby regulator uses an Isolated Collector
Vertical PNP transistor as the regulating element.
This structure allows a very low dropout voltage at
currents up to 50mA. The dropout operation of the
standby regulator is maintained down to 2V input
supply voltage. The output voltage is regulated up
to the transient input supplyvoltageof 40V. This fea-
ture avoids functional interruptions which could be
generated by overvoltage pulses.

The typical curve of the standby output voltage as
a functionof the input supply voltage is shownin fig.
1.

The current consumption of the device (quiescent
current) is less than 250

A when output 2 is dis-

abled (standby mode). The dropout voltage is con-
trolled to reduce the quiescent current peak in the
undervoltage region and to improve the transient
response in this region.

The quiescent current is shown in fig.2 as a function
of the supply input voltage 2.

OUTPUT 2 VOLTAGE

The output 2 regulator uses the same output struc-
ture as the standby regulator, but rated for an output
current of 500mA.

The output 2 regulator works in tracking mode with
the standby output voltage as a reference voltage.

The output 2 regulator can be switched off via the
Enable input.

L4937N

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Figure 1 : Output Voltage vs. Input Voltage.

Figure 2 : Quiescent Current vs. Supply Voltage.

RESET CIRCUIT

The block circuit diagramof the resetcircuit is shown
in fig.3. The reset circuit supervisesthe standbyout-
put voltage. The reset threshold of 4.7V is defined
by the internal reference voltage and the standby
output divider.

The reset pulse delay time t

, is defined by the

charge time of an external capacitor C

x 2V

The reaction time of the reset circuit dependson the
discharge time limitation of the reset capacitor C

and is proportional to the value of C

The reaction time of the reset circuit increases the
noise immunity. In fact, if the standbyoutput voltage
drops below the reset threshold for a time shorter
than the reaction time t

, no reset output variation

occurs. The nominal reset delay is generated for
standby output voltage drops longer than the time
necessary for the complete discharging of the ca-
pacitor C

. This time is typically equal to 50

s if C

= 100nF. The typical reset output waveforms are
shown in fig.

400

200

L4937N

6/9

Heptawatt V

DIM.

inch

MIN.

TYP.

MAX.

MIN.

TYP.

MAX.

4.8

0.189

1.37

0.054

2.4

2.8

0.094

0.110

1.2

1.35

0.047

0.053

0.35

0.55

0.014

0.022

0.7

0.97

0.028

0.038

0.6

0.8

0.024

0.031

0.9

0.035

2.34

2.54

2.74

0.095

0.100

0.105

4.88

5.08

5.28

0.193

0.200

0.205

7.42

7.62

7.82

0.295

0.300

0.307

10.4

0.409

10.05

10.4

0.396

0.409

16.7

16.9

17.1

0.657

0.668

0.673

14.92

0.587

21.24

21.54

21.84

0.386

0.848

0.860

22.27

22.52

22.77

0.877

0.891

0.896

1.29

0.051

2.6

2.8

0.102

0.110

0.118

15.1

15.5

15.8

0.594

0.610

0.622

6.35

6.6

0.236

0.250

0.260

0.2

0.008

2.55

2.8

3.05

0.100

0.110

0.120

4.83

5.08

5.33

0.190

0.200

0.210

(typ.)

Dia

3.65

3.85

0.144

0.152

Dia.

HEPTAMEC

OUTLINE AND

MECHANICAL DATA

L4937N

8/9

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the conse-
quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this
publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi-
croelectronics products are not authorized for use as critical components in life support devices or systems without express written
approval of STMicroelectronics.

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HEPTAWATT

is a Trademark of STMicroelectronics

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