ZXCL SERIES

Issue 8 - October 2007

9

www.zetex.com

© Zetex Semiconductors plc 2007

Applications information

Enable control

A TTL compatible input is provided to allow the

regulator to be shut down. A low voltage on the

Enable pin puts the device into shutdown mode.

In this mode the regulator circuit is switched off

and the quiescent current reduces to virtually

zero (typically less than 10nA) for input voltages

above the minimum operating threshold of the

device. A high voltage on the Enable pin ensures

normal operation.

driven from an independent source of up to 10V

maximum.

(e.g.

CMOS

logic)

for

normal

operation. There is no clamp diode from the

voltage within its operating range irrespective

of the voltage on the Enable pin. However input

voltage rise time should be kept below 5ms to

ensure consistent start-up response.

Current Limit

The ZXCL devices include a current limit circuit

which restricts the maximum output current

flow to typically 230mA. Practically the range of

over-current should be considered as minimum

160mA to maximum 800mA. The device’s

robust design means that an output short circuit

tolerated for an indefinite period.

Thermal Overload

Thermal overload protection is included on

chip. When the device junction temperature

exceeds a minimum 125°C the device will shut

down. The sense circuit will re-activate the

output as the device cools. It will then cycle until

the overload is removed. The thermal overload

protection will be activated when high load

currents or high input to output voltage

differentials cause excess dissipation in the

device.

Start up delay

A small amount of hysteresis is provided on the

Enable pin to ensure clean switching. This

feature can be used to introduce a start up delay

if required. Addition of a simple RC network on

the Enable pin provides this function. The

following

diagram

illustrates

this

circuit

connection. The equation provided enables

calculation of the delay period.

Figure 1 Circuit Connection

R

C

T

= RCIn

V

V

1.5

d(NOM)

IN

⎛

⎝

⎜

⎞

⎠

⎟

Calculation of start up delay as above