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 of each regulator. 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

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.

ISSUE 5 - NOVEMBER 2001

ZXCL250 ZXCL260 ZXCL280

ZXCL300 ZXCL330 ZXCL400

7

VIN

EN

VO

U1

ZXCL SERIES

Q1

FMMT717

R1

5.6R

C2

1uF

C1

1uF

C3

1uF

VOUT

VIN

Scheme to boost output current to 2A