CS8140 데이터 시트보기 (PDF) - Cherry semiconductor

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CS8140

5V, 500mA Linear Regulator with ENABLE, , and Watchdog RESET

Cherry semiconductor 

Definition of Terms

Dropout Voltage

The input-output voltage differential at which the circuit

ceases to regulate against further reduction in input volt-

age. Measured when the output voltage has dropped

100mV from the nominal value obtained at 14V input,

dropout voltage is dependent upon load current and junc-

tion temperature.

Input Voltage

The DC voltage applied to the input terminals with respect

to ground.

Line Regulation

The change in output voltage for a change in the input

voltage. The measurement is made under conditions of

low dissipation or by using pulse techniques such that the

average chip temperature is not significantly affected.

Load Regulation

The change in output voltage for a change in load current

at constant chip temperature.

Quiescent Current

The part of the positive input current that does not con-

tribute to the positive load current. The regulator ground

lead current.

Ripple Rejection

The ratio of the peak-to-peak input ripple voltage to the

peak-to-peak output ripple voltage.

Current Limit

Peak current that can be delivered to the output.

Circuit Description

Voltage Reference and Output Circuitry

Precision Voltage Reference

circuitry insures that the output current never exceeds a

preset limit.

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 main-

tained within ±4% over temperature and supply variation.

> 30V

VIN

Output Stage

VOUT

The composite PNP-NPN output structure (Figure1) pro-

vides 500mA (min) of output current while maintaining a

low drop out voltage (1.25V) and drawing little quiescent

IO

current (7mA).

VIN

Load

Dump

Short

Circuit

Thermal

Shutdown

Figure 2: Typical Circuit Waveforms for Output Stage Protection.

VOUT

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.

Figure 1: Composite Output Stage of the CS8140/1

The NPN pass device prevents deep saturation of the out-

put stage which in turn improves the ICÕs efficiency by

preventing 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).

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

Regulator Control Functions

The CS8140 differs from all other linear regulators in its

unique combination of control features.

Watchdog and ENABLE Functions

VOUT is controlled by the logic functions ENABLE and

Watchdog (Table 1).

ENABLE

H

L

Slow

5

0

VOUT (V)

Normal

5

5

WDI

Fast

5

0

High

5

0

Table 1: VOUT as a Function of ENABLE and Watchdog

Low

5

0

6

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