ZXCL200 datasheet(6/9 Pages) ZETEX

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Input to Output Diode

In common with many other regulators, the ZXCL200

device has an inherent diode associated with the

output series pass transistor. This diode has its anode

connected to the output and its cathode to the input.

The internal diode is normally reverse biased, but will

conduct if the output is forced above the input by more

than a VBE (approximately 0.6V). Current will then flow

from Vout to Vin. For safe operation, the maximum

current in this diode should be limited to 5mA

continuous and 30mA peak. An external schottky diode

may be used to provide protection when this condition

cannot be satisfied.

Increased Output current

Any ZXCL series device may be used in conjunction

with an external PNP transistor to boost the output

current capability. In the application circuit

shown

below, a FMMT717 device is employed as the external

pass element. This SOT23 device can supply up to 2.5A

maximum current subject to the thermal dissipation

limits of the package (625mW). Alternative devices

may be used to supply higher levels of current. Note

that with this arrangement, the dropout voltage will be

increased by the VBE drop of the external device. Also,

care should be taken to protect the pass transistor in

the event of excessive output current.

ZXCL200

ISSUE 1 - SEPTEMBER 2001

VIN

ZXCL SERIES

FMMT717

5.6R

1uF

VOUT

VIN

Scheme to boost output current to 2A

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