This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
L4938N/ND
L4938NPD
April 1999
DUAL MULTIFUNCTION VOLTAGE REGULATOR
.
STANDBYOUTPUT VOLTAGEPRECISION 5V
2%
.
OUTPUT 2 TRACKED TO THE STANDBY OUT-
PUT
.
OUTPUT
2
DISABLE
FUNCTION
FOR
STANDBY MODE
.
VERY LOW QUIESCENT CURRENT, LESS
THAN 250
A, IN STANDBY MODE
.
OUTPUT 2 VOLTAGE SETTABLE FROM 5 TO
20V
.
OUTPUT CURRENTS : I
01
= 50mA, I
02
= 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
.
EARLY WARNING OUTPUT FOR SUPPLY UN-
DERVOLTAGE
.
THERMAL SHUTDOWN AND SHORT CIRCUIT
PROTECTIONS
PowerDIP
(12+2+2)
ORDERING NUMBERS: L4938N (PDIP)
L4938ND (SO)
L4938NPD (PSO20)
DESCRIPTION
The L4938N is a monolithic integrated dual voltage
regulatorswith two very low dropout outputsand ad-
ditional functions such as power-on reset and input
voltage sense. They are designedfor supplying mi-
crocomputer controlled systems specially in auto-
motive applications.
PIN CONNECTION (top view)
SO20
(12+4+4)
N.C.
CT
EN
GND
GND
SO
RES
1
3
2
4
5
6
7
V
O2
GND
V
O2
GND
V
S2
V
S1
SI
16
15
14
13
12
10
11
D95AT156
V
O1
8
ADJ
9
POWERDIP
N.C.
C7
EN
GND
GND
GND
GND
RES
SO
V
S1
V
S2
GND
GND
GND
GND
V
O2
V
O2
ADJ
1
3
2
4
5
6
7
8
9
18
17
16
15
14
12
13
11
19
10
20
V
O1
SI
D93AT004
SO20
PowerSO20
GND
N.C.
N.C.
V
S2
V
S1
N.C.
SI
CT
EN
N.C.
GND
10
8
9
7
6
5
4
3
2
13
14
15
16
17
19
18
20
12
1
11
GND
D95AT169A
N.C.
RESET
V
O1
SO
ADJ
V
O2
N.C.
GND
PowerSO20
1/12
BLOCK DIAGRAM
REG1
1.23V
REFERENCE
REG2
RESET
2.0V
1.23V
1.23V
SENSE
(optional)
V
S1
V
S2
EN
SI
SO
RES
CT
ADJ
V
O2
V
O1
GND
D94AT143A
2
THERMAL DATA
Symbol
Parameter
Powerdip
PowerSO20
SO20
Unit
R
thj-case
R
thj-amb
Thermal Resistance Junction-Case
Max.
Thermal Resistance Junction-Ambient
Max.
14
90
< 2
20
C/W
C/W
L4938N - L4938ND - L4938NPD
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ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
S
DC Supply Voltage
28
V
Transient Supply Voltage (T < 1s)
40
V
T
j
, T
stg
Junction and Storage Temperature Range
55 to 150
C
I
SI
Sense Input Current (V
SI
0.3V or V
SI
> V
S
)
1
mA
I
EN
Enable Input Current (V
EN
0.3V)
1
mA
V
EN
Enable Input Voltage
V
S
V
RES
, V
SO
Reset and Sense Output Voltage
20
V
I
RES
, I
SO
Reset and Sense Output Current
5
mA
P
D
Power Dissipation
875
mW
REG1
1.23V
REFERENCE
REG2
RESET
2.0V
1.23V
1.23V
SENSE
(optional)
V
S1
V
S2
EN
SI
SO
RES
CT
ADJ
V
O2
V
O1
GND
D94AT144A
C
S
CT
C
O2
C
O1
R
RES
R
SO
2
V
O1
APPLICATION CIRCUIT
C
S
1
F ; C
01
6
F ; C
02
10
F, ESR < 10
at 10KHz
Note : The circuit is ESD protected according to MILSTD883C.
L4938N - L4938ND - L4938NPD
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ELECTRICAL CHARACTERISTICS (V
S
= 14V; 40
C
T
J
125
C unless otherwise specified)
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
S
Operating Supply Voltage
25
V
V
O1
Standby Output Voltage
6V
V
S
25V
1mA
I
O1
50mA
4.90
5.00
5.10
V
V
O2
- V
O1
Output Voltage 2 Tracking Error
(note 1)
6V
V
S
25V
5mA
I
O2
500mA
Enable = LOW
25
+25
mV
I
ADJ
ADJ Input Current
I
O1
= 1mA; I
O2
= 5mA
1
0.1
1
A
V
DP1
Dropout Voltage 1
I
O1
= 10mA
I
O1
= 50mA
0.1
0.2
0.25
0.4
V
V
V
IO1
Input to Output Voltage
Difference in Undervoltage
Condition
VS = 4V, I
O1
= 35mA
0.4
V
V
DP2
Dropout Voltage 2
IO1 = 100mA
I
O1
= 500mA
0.2
0.3
0.3
0.6
V
V
V
IO2
Input to Output Voltage
Difference in Undervoltage
Condition
VS = 4.6V, I
O1
= 350mA
0.6
V
V
OL 1.2
Line Regulation
6V
V
S
25V
I
O1
= 1mA; I
O2
= 5mA
20
mV
V
OLO1
Load Regulation 1
1mA
I
O1
50mA
25
mV
V
OLO2
Load Regulation 2
5mA
I
O2
500mA
50
mV
I
LIM1
Current Limit 1
V
O1
= 4.5V
V
O1
= 0V (note 2)
55
25
100
50
200
100
mA
mA
I
LIM2
Current Limit 2
VO2 = 0V
550
1000
1700
mA
I
QSB
Quiescent Current Standby Mode
(output 2 disabled)
I
O1
= 0.3mA; T
J
< 100
C
V
EN
2.4V
V
S
= 14V
V
S
= 3.5V
210
340
290
850
A
A
I
Q
Quiescent Current
I
O1
= 50mA
I
O1
= 500mA
30
mA
ENABLE
V
ENL
Enable Input LOW Voltage
(output 2 active)
0.3
1.5
V
V
ENH
Enable Input HIGH Voltage
2.4
7
V
V
ENhyst
Enable Hysteresis
30
75
200
mV
I
EN
Enable Input Current
0V < V
EN
< 1.2V
2.5V < V
EN
< 7V
10
1
1.5
0
0.5
+1
A
A
L4938N - L4938ND - L4938NPD
4/12
FUNCTIONAL DESCRIPTION
The L4938N is based on the STMicroelectronics
modular voltage regulator approach. Several out-
standing features and auxiliary functions are pro-
vided to meet the requirements of supplying the mi-
croprocessor systems used in automotive applica-
tions.
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 transientinput 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 theinput supply voltage is shown in 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 quiescentcurrent 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 standbyregulator, 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
when the output 2 programming pin ADJ is con-
nected to V
O2
. By connecting a resistor divider R
1
,
R
2
to the pin ADJ as shown in fig. 3, the output volt-
age 2 can be programmed to the value :
V
O2
= V
O1
(1 + R
1
/R
2
)
The output 2 regulator can be switched off via the
Enable input.
If a fixed 5 regulation is required ADJ Pin has to be
connected to V
02
Pin.
Note : 1 : V
O2
connected to ADJ.V
O2
can be set to higher values by inserting an external resistor divider.
2 : Foldback characteristic
ELECTRICAL CHARACTERISTICS (continued)
RESET
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
V
Rt
Reset Low Threshold Voltage
V
o1
-0.4
4.7
V
o1
-0.1
V
V
Rth
Reset Threshold Hysteresis
50
100
200
mV
t
RD
Reset Pulse Delay
C
T
= 100nF; t
R
> 100
s
55
100
180
mV
t
RR
Reset Reaction Time
C
T
= 100nF
1
10
50
s
V
RL
Reset Output LOW Voltage
R
RES
= 10K
to V
01
V
S
= 1.5V
0.4
V
I
LRES
Reset Output HIGH Leakage
V
RES
= 5V
1
A
V
CTh
Delay Comparator Threshold
2.0
V
V
CTh, hyst
Delay Comparator Threshold
Hysteresis
100
mV
SENSE
V
Slth
Sense Threshold Voltage
1.16
1.23
1.35
V
V
Slth, hyst
Sense Threshold Hysteresis
40
100
200
mV
V
SOL
Sense Output LOW Voltage
V
SI
= 1,16V; V
S
3V
R
SO
= 10K
to V
01
0.4
V
I
LSO
Sense Output Leakage
V
SO
= 5V; V
SI
1.5V
1
A
L4938N - L4938ND - L4938NPD
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