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PDF CS8121YTFVA5 Data sheet ( Hoja de datos )
| Número de pieza | CS8121YTFVA5 | |
| Descripción | 5V/ 1A Linear Regulator with and ENABLE RESET | |
| Fabricantes | Cherry Semiconductor Corporation | |
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CS8121
5V, 1A Linear Regulator
with RESET and ENABLE
Description
Features
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).
The CS8121Õs 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-
torÕs pass transistor and sends the IC
into Sleep mode where it draws only
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 VOUT = 1V.
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.
The CS8121 is fault protected against
short circuit, over voltage and thermal
runaway conditions.
s 5V ± 4% Output Voltage
s Low Dropout Voltage
(1.2V @ 1A)
s Low Quiescent Current
(4mA @ IOUT = 1A)
s µP Compatible Control
Functions
RESET
ENABLE
s Low Current Sleep Mode
IQ = 250µA
s Fault Protection
Thermal Shutdown
Short Circuit
60V Peak Transient
Voltage
Block Diagram
Package Options
5 Lead TO-220
5 Lead TO-220
Overmolded
VIN
ENABLE
RESET
ENABLE
Comparator
Over
Voltage
Shutdown
Bandgap
Supply
VREF
Thermal
Shutdown
TO VOUT
Bandgap
Reference
RESET
Comparator +
-
Output
Current
Limit
- + Error
Amplifier
Rev. 5/4/99
1
VOUT
5 Lead
TO-220
VOUT(SENSE)
Gnd
1 VIN
2 ENABLE
3 Gnd
4 RESET
1 5 VOUT
1
7 Lead D2PAK
1
1 NC
2 VIN
3 ENABLE
4 Gnd
5 RESET
6 VOUT
7 VOUT(SENSE)
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: [email protected]
Web Site: www.cherry-semi.com
A ¨ Company
1 page  
Circuit Description: continued
If the input voltage rises above 30V (e.g. load dump), the
output shuts down. This response protects the internal cir-
cuitry and enables the IC to survive unexpected voltage
transients.
Using an emitter sense scheme, the amount of current
through the NPN pass transistor is monitored. Feedback
circuitry insures that the output current never exceeds a
preset limit.
Should the junction temperature of the power device
exceed 180ûC (typ) the power transistor is turned off.
Thermal shutdown is an effective means to prevent die
overheating since the power transistor is the principle
heat source in the IC.
Regulator Control Functions
The CS8121 contains two microprocessor compatible con-
trol functions: ENABLE and RESET (Figure 3).
RESET Function
A RESET signal (low voltage) is generated as the IC pow-
ers up (VOUT > VOUT - 100mV) or when VOUT drops out of
regulation (VOUT < VOUT - 140mV, typ). 40mV of hysteresis
is included in the function to minimize oscillations.
The RESET output is an open collector NPN transistor,
controlled by a low voltage detection circuit. The circuit is
functionally independent of the rest of the IC, thereby
guaranteeing that the RESET signal is valid for VOUT as
low as 1V.
An external RC network on the RESET lead (Figure 4) pro-
vides a sufficiently long delay for most microprocessor
based applications. RC values can be chosen using the
following formula:
[ ( ) ]RTOT´CRST
ln
ÐtDelay
VT Ð VOUT
VRST Ð VOUT
VIN
ENABLE
VOUT
HI
VIN(HI)
LO
VRT(ON)
VRT(OFF)
FOR 7V < VIN < 26V
where:
RTOT = RRST in parallel with RIN,
RIN = µP port impedance,
CRST = RESET delay capacitor,
tDelay = desired delay time,
VRST = VSAT of RESET lead (0.7V @ turn - on), and
VT = µP logic threshold voltage.
RESET
VR PEAK
(1)
(2)
VR SAT
(1) = NO RESET DELAY CAPACITOR
(2) = WITH RESET DELAY CAPACITOR
Figure 3. Circuit Waveforms for the CS8121
VR PEAK
ENABLE Function
The ENABLE function switches the output transistor.
When the voltage on the ENABLE lead exceeds 2.9V typ,
the output pass transistor turns off, leaving a high
impedance facing the load. The IC will remain in Sleep
mode, drawing only 250µA, until the voltage on the lead
drops below 2.1V typ. Hysteresis (800mV) is built into the
ENABLE function to provide good noise immunity.
VOUT
CS8121
RESET
RRST
CRST
Figure 4. RC Network for RESET Delay
5V to mP
and
System
10mF Power
tantalum
to mP
RESET
Port
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet CS8121YTFVA5.PDF ] | |
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