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CS8121
CS8121
Description
The CS8121 is a 5V, 1A precision linear
regulator with two microprocessor
compatible control functions and pro-
tection circuitry included on chip. The
composite NPN-PNP output pass tran-
sistor assures a lower dropout voltage
(1.2V @ 1A) without requiring exces-
sive supply current (4mA).
DE
SI
GN
1
5V, 1A Linear Regulator
with RESET and ENABLE
Features
EW
AR
CH
IV
FO
E
R
N
RE
CO
MM
EN
DE
D
Block Diagram
Over
Voltage
Shutdown
Output
Current
Limit
-
+
Error
Amplifier
Bandgap
Supply
Thermal
Shutdown
Bandgap
Reference
RESET
Comparator
+
-
250µA.
RESET
sends a
RESET
signal
when the IC is powering up or when-
ever the output voltage falls out of reg-
ulation. The
RESET
signal is valid
down to V
OUT
= 1V.
s
5V ± 4% Output Voltage
s
Low Dropout Voltage
(1.2V @ 1A)
s
Low Quiescent Current
(4mA @ I
OUT
= 1A)
The CS8121’s two logic control func-
tions make this regulator well suited to
applications requiring microprocessor-
based control at the board or module
level.
ENABLE
controls the output
stage. A high voltage (>2.9V) on
the
ENABLE
lead turns off the regula-
tor’s pass transistor and sends the IC
into Sleep mode where it draws only
The CS8121 design optimizes supply
rejection by switching the internal
bandgap reference from the supply
input to the regulator output as soon as
the nominal output voltage is achieved.
Additional on chip filtering enhances
rejection of high frequency transients
on all external leads.
s
µP Compatible Control
Functions
RESET
ENABLE
s
Low Current Sleep Mode
I
Q
= 250µA
s
Fault Protection
Thermal Shutdown
Short Circuit
60V Peak Transient
Voltage
The CS8121 is fault protected against
short circuit, over voltage and thermal
runaway conditions.
Package Options
5 Lead TO-220
V
OUT
V
IN
5 Lead
TO-220
NO
T
1 V
IN
V
OUT(SENSE)
DE
VI
CE
VREF
RESET
December, 2001 - Rev. 7
+
-
ENABLE
ENABLE
Comparator
2
ENABLE
3 Gnd
1
4 RESET
5 V
OUT
1 NC
2 V
IN
3
ENABLE
4 Gnd
TO V
OUT
7 Lead D
2
PAK
Gnd
5 RESET
6 V
OUT
7 V
OUT(SENSE)
ON Semiconductor
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885–3600 Fax: (401)885–5786
N. American Technical Support: 800-282-9855
Web Site: www.cherry–semi.com
1
CS8121
Absolute Maximum Ratings
DC Input Voltage ...........................................................................................................................................................-0.7 to 26V
Peak Transient Voltage (46V Load Dump).............................................................................................................................60V
Output Current .................................................................................................................................................Internally Limited
Electrostatic Discharge (Human Body Model) ......................................................................................................................2kV
Operating, Temperature ..........................................................................................................................................-40C to 125°C
Junction Temperature...............................................................................................................................................-40C to 150°C
Storage Temperatures.............................................................................................................................................-55°C to 150°C
Lead Temperature Soldering
Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260°C peak
Reflow (SMD styles only) ......................................................................................60 sec. max above 183°C, 230°C peak
Electrical Characteristics:
I
OUT
= 5mA, -40°C
≤
T
J
≤150°C
, 7V
≤
V
IN
≤
26V, -40°C
≤
T
A
≤
125°C unless otherwise specified
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
s
Output Stage
Output Voltage, V
OUT
Line Regulation
Load Regulation
Supply Voltage Rejection
Dropout Voltage
Quiescent Current
7V
≤
V
IN
≤
26V, 1mA
≤
I
OUT
≤
1A
7V
≤
V
IN
≤
26V, I
OUT
= 5mA
5mA
≤
I
OUT
≤
1A
V
IN
= 14V
DC
+ 1V
RMS
@120Hz, I
LOAD
= 50Ω
I
OUT
= 1A
ENABLE = High, V
IN
= 12V
ENABLE = Low, I
OUT
= 1A
54
4.8
5.0
0
10
70
1.2
0.25
4
1.8
0.65
20
5.2
50
70
V
mV
mV
dB
V
mA
mA
s
Protection Circuits
Short Circuit Current
Thermal Shutdown
Overvoltage Shutdown
s
RESET
RESET Saturation Voltage
RESET Output Leakage
Current
Power ON/OFF RESET
Peak Output Voltage
RESET Threshold ON
(V
OUT
Increasing)
RESET Threshold OFF
(V
OUT
Decreasing)
RESET Threshold Hysteresis
s
ENABLE
Input High Voltage
Input Low Voltage
Input Hysteresis
Input Current
7V < V
IN
< 26V
7V < V
IN
< 26V
7V < V
IN
< 26V
Gnd < V
IN(HI)
< V
OUT
1.1
0.4
2.9
2.1
0.8
0
2.8
±10
3.9
V
V
V
µA
4.75
10
1V < V
OUT
< V
RT(OFF),
3.1kΩ pull-up
to V
OUT
ENABLE = Low
V
OUT
> V
RT(ON)
, V
RESET
= V
OUT
3.1kΩ pull-up to V
OUT
0.1
0
0.7
V
OUT
- 0.10
V
OUT
- 0.14
40
0.4
25
1.0
V
OUT
- 0.04
V
µA
V
V
V
mV
150
26
1.5
190
40
A
°C
V
2
CS8121
Package Lead Description
PACKAGE LEAD #
LEAD SYMBOL
FUNCTION
7 Lead
D
2
PAK
1
2
3
4
5
5 Lead TO-220
NC
1
2
3
4
V
IN
ENABLE
Gnd
RESET
No Connection.
Supply voltage to IC, usually direct from the battery.
CMOS compatible logical. V
OUT
is disabled i.e. placed in a
high impedance state when ENABLE is high.
Ground connection.
CMOS compatible output lead. RESET goes low whenever
V
OUT
falls out of regulation. The RESET delay is externally
programmed.
Regulated output voltage, 5V (typ).
Remote sensing of output voltage.
6
7
5
V
OUT
V
OUT(SENSE)
Typical Performance Characteristics
Output Voltage vs. Temperature
5.02
Load Regulation vs. Output Current Over Temperature
0
I
OUT
= 100mA
5.01
-5
-10
-15
Load Reg. (mV)
-20
-25
-30
-35
-40
-45
V
IN
=14V
125
°
C
–40
°
C
5.00V @ 25˚C
V
OUT
(V)
5
4.99
4.98
4.97
4.96
4.95
-40
25
°
C
-20
0
20
40
60
80
100
120 140 150
-50
0
200
400
I
OUT
(A)
600
800
1A
Junction Temperature (˚C)
Line Regulation vs. Output Current Over Temperature
Dropout Voltage vs. Output Current Over Temperature
1.5
50
V
IN
= 7 to 26V
40
Line Reg. (mV)
Dropout Voltage (V)
1.4
1.3
1.2
30
20
125˚C
10
-40˚C
0
-10
0
0.2
0.4
0.6
0.8
1A
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
0.1
0.2
0.3
0.4
0.5
0.6
I
OUT
(A)
0.7
0.8
0.9
1.0
-40°C
25°C
125°C
25˚C
I
OUT
(A)
3
CS8121
Typical Performance Characteristics: continued
Quiescent Current vs. Output Current Over Temperature
Output Voltage and Supply Current vs. Input Voltage
3.5
3.0
Quiescent Current (mA)
-40°C
2.5
25°C
2.0
125°C
1.5
V
OUT
16.0
4.0
3.0
2.0
1.0
I
Q
12.0
8.0
4.0
0.0
10.0
1.0
0.5
VIN = 14V
0.0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0
0.0
I
OUT
2.0
4.0
6.0
8.0
Supply Voltage
RESET Output Voltage vs. Output Current
2000
1800
Reset Output Voltage (mV)
1600
1400
1200
1000
800
600
400
200
0
1
5
10
15
20
25
30
35
40
Reset Output Current (mA)
V
IN
= 5V
Circuit Description
Voltage Reference and Output Circuitry
Precision Voltage Reference
The regulated output voltage depends on the precision
band gap voltage reference in the IC. By adding an error
amplifier into the feedback loop, the output voltage is
maintained within ±4% over temperature and supply vari-
ation.
Output Stage
The composite PNP-
NPN output structure
(Figure 1) provides 1A
(typ) of output current
while maintaining a
low drop out voltage
(1.2V) and drawing lit-
tle quiescent current
(4mA).
V
OUT
The NPN pass device prevents deep saturation of the output
stage which in turn improves the IC’s efficiency by prevent-
ing excess current from being used and dissipated by the IC.
Output Stage Protection
The output stage is protected against overvoltage, short
circuit and thermal runaway conditions (Figure 2).
> 30V
V
IN
V
IN
V
OUT
I
OUT
Load
Dump
Short
Circuit
Thermal
Shutdown
Figure 1. Composite Output Stage of the CS8121
Figure 2. Typical Circuit Waveforms for Output Stage Protection.
4
Supply Current (mA)
5.5
5.0
22.0
20.0
V
OUT
(V)
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