CS8128YD8 Cherry Semiconductor Corporation, CS8128YD8 Datasheet - Page 5

• Manufacturer Part Number: CS8128YD8
• Description: 5V Linear Controller/Driver
• Manufacturer: Cherry Semiconductor Corporation

The CS8128 includes an over voltage shutdown circuit
which is activated by connecting the SHUTDOWN lead to
the input. Shutdown typically occurs at 36V. Grounding
the SHUTDOWN lead disables this function. With the
overvoltage shutdown disabled, the CS8128 will continue
to regulate during an overvoltage condition.
The CS8128 includes a thermal shutdown circuit that dis-
ables the output when junction temperature exceeds
approximately 180˚C. This is a self-protection feature
designed to protect the CS8128. The thermal shutdown cir-
cuit does not monitor the temperature of the pass transis-
tor, which will probably be much hotter. To optimize ther-
mal shutdown, board design should minimize the differ-
ence in temperature of the CS8128 and the pass device.
External Pass Device - Select a pass device that will deliv-
er the desired output current, withstand the maximum
expected input voltage, and dissipate the resulting power.
The CS8128 is compatible with a wide variety of Bipolar
and FET pass transistors.
Output Capacitor - An output capacitor is required for sta-
bility in most applications. Though a 10µF capacitor should
be sufficient, regulator stability is dependent on the
characteristics of the pass transistor. Capacitor effective
series resistance (ESR) also factors in system stability. Some
bench work may be required to determine the capacitor
characteristics required for use in a particular application.
BIAS Resistor - This resistor provides bias current for the
CS8128 output stage, and prevents the pass device from
External Component Selection
Overvoltage Shutdown
Thermal Shutdown
V
RESET
(5V)
V
OUT
IN
C
0.022µF
Delay
10µF
C
O
R
4.7 kΩ
RST
Application Information
R
220Ω
IN
Test Circuit
V
Sense
Delay
RESET
IN
C
0.022µF
IN
5
CS8128
“leaking”. It also speeds the turn-off of the pass device
during an overvoltage transient. For proper operation over
temperature, the recommended value is 560Ω, although it
may be increased or decreased for a particular application.
R
available to the pass transistor. It also determines regula-
tor start-up current and short circuit current limit. For
bipolar pass transistors, it can be selected by use of the fol-
lowing formulae:
***β
current.
Typical start-up current and current limit can be calculat-
ed as follows:
For example, if the minimum input voltage is 6V, maxi-
mum output current is 1Amp, and minimum transistor
β @ 1Amp is 60, then R
With V
limit:
TIP42B
OUT
Q1
Resistor - This resistor controls the drive current
= Pass transistor minimum β @ maximum output
SHUTDOWN
IN
R
Pwr Gnd
Ref Gnd
OUT
= 14V, and a pass transistor β of 40 @ current
I
V
Limit
OUT
I
I
Start
Limit
=
R
≈
OUT
V
≈
I
V
≈
IN(min)
START
I
IN
OUT(max)
R
≈
R
560Ω
R
220Ω
14V – 1V
BIAS
OUT
OUT
300Ω
– 1V
300Ω
OUT
4V
6V – 1V
1Amp
≈
– 1V
can be calculated as follows:
x ß
R
4V
OUT
+ 5mA = 18.3mA
Q1
x ß
x 40 = 1.7Amps
Gnd
@ Current Limit
x 60 = 300Ω
Q1
+ 5mA
***