ZXCL SERIES

Issue 8 - October 2007

8

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© Zetex Semiconductors plc 2007

Scheme to boost output current to 2A

Input to Output Diode

In common with many other LDO regulators, the

ZXCL 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

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

Also, care should be taken to protect the pass

transistor in the event of excessive output

current.