CS403 Datasheet, PDF(4/6 Page) Cherry Semiconductor Corporation

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CS403 Datasheet, PDF (4/6 Pages) Cherry Semiconductor Corporation – 5V, 750mA Linear Regulator with RESET

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Circuit Description

The CS403 RESET function is very precise, has hysteresis

on both the RESET and Delay comparators, a latching

Delay capacitor discharge circuit, and operates down to

1V.

The RESET circuit output is an open collector type with

ON and OFF parameters as specified. The RESET output

NPN transistor is controlled by the two circuits described

(see Block Diagram).

Low Voltage Inhibit Circuit

This circuit monitors output voltage, and when output

voltage is below the specified minimum, causes the

RESET output transistor to be in the ON (saturation) state.

When the output voltage is above the specified level, this

circuit permits the RESET output transistor to go into the

OFF state if allowed by the reset Delay circuit.

Reset Delay Circuit

This circuit provides a programmable (external capacitor)

delay on the RESET output lead. The Delay lead provides

source current to the external delay capacitor only when

the Low Voltage Inhibit circuit indicates that output volt-

age is above VRT(ON). Otherwise, the Delay lead sinks cur-

rent to ground (used to discharge the Delay capacitor).

The discharge current is latched ON when the output volt-

age is below VRT(OFF), or when the voltage on the Delay

capacitor is above VDIS. In other words, the Delay capaci-

tor is fully discharged any time the output voltage falls

out of regulation, even for a short period of time. This fea-

ture ensures a controlled RESET pulse is generated follow-

ing detection of an error condition. The circuit allows

the RESET output transistor to go to the OFF (open) state

only when the voltage on the Delay lead is higher than

VDIS.

Test Circuit

C1*

100nF

VIN

VOUT

CS403

Delay

RESET

Gnd

C2**

COUT =10mF to

100mF

C1* is required if the regulator is far from the power source filter.

C2** is required for stability

Application Notes

Stability Considerations

The output or compensation capacitor helps determine

three main characteristics of a linear regulator: start-up

delay, load transient response and loop stability.

The capacitor value and type should be based on cost,

availability, size and temperature constraints. A tantalum

or aluminum electrolytic capacitor is best, since a film or

ceramic capacitor with almost zero ESR, can cause insta-

bility. The aluminum electrolytic capacitor is the least

expensive solution, but, if the circuit operates at low tem-

peratures (-25Â¡C to -40Â¡C), both the value and ESR of the

capacitor will vary considerably. The capacitor manufac-

turers data sheet usually provides this information.

The value for the output capacitor COUT shown in the test

and applications circuit should work for most applica-

tions, however it is not necessarily the optimized solution.

To determine an acceptable value for COUT for a particular

application, start with a tantalum capacitor of the recom-

mended value and work towards a less expensive alterna-

tive part.

Step 1: Place the completed circuit with a tantalum capac-

itor of the recommended value in an environmental cham-

ber at the lowest specified operating temperature and

monitor the outputs with an oscilloscope. A decade box

connected in series with the capacitor will simulate the

higher ESR of an aluminum capacitor. Leave the decade

box outside the chamber, the small resistance added by

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