ZXCL250 Datasheet, PDF (7/11 Pages) Zetex Semiconductors – ULTRA SMALL MICROPOWER SC70 LOW DROPOUT REGULATORS

ZXCL250 ZXCL260 ZXCL280
ZXCL300 ZXCL330 ZXCL400
Input to Output Diode
Increased Output current
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
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.
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.
VIN
Q1
FMMT717
R1
5.6R
C3
1uF
C2
1uF
U1
ZXCL SERIES
VIN
VO
EN
Scheme to boost output current to 2A
VOUT
C1
1uF
ISSUE 5 - NOVEMBER 2001
7