EUP7982
Adjustable Operation
Fault Detection
The adjustable version of the EUP7982 has an output
voltage range of 1.25V to 6V. The output voltage of the
EUP7982 adjustable regulator is programmed using an
external resistor divider as shown in Figure3. The output
voltage is calculated using:
The EUP7982 provides a FAULT pin that goes low
during out of regulation conditions like current limit and
thermal shutdown, or when it approaches dropout. The
latter monitors the input-to-output voltage differential
and compares it against a threshold that is slightly above
the dropout voltage. This threshold also tracks the
dropout voltage as it varies with load current. Refer to
Fault Detect vs. Load Current curve in the typical
characteristics section.
The FAULT pin requires a pull-up resistor since it is an
open-drain output. This resistor should be large in value
to reduce energy drain. A100kΩ pull-up resistor works
well for most applications.
R
1
V = V ×(1+
)
O
ref
R
2
Where:
Vref=1.23V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
V
O
Shutdown
P = R
−1
I
2
1.23V
The EUP7982 goes into sleep mode when the
pin
SHDN
is in a logic low condition. During this condition, the
pass transistor, error amplifier, and bandgap are turned
off, reducing the supply current to 60nA typical. The
Choose R2=100k to optimize accuracy, power supply
rejection, noise and power consumption.
In order to improve the stability of the adjustable version,
it is suggested that a small compensation capacitor C1 be
placed between OUT and SET
pin may be directly tied to VIN to keep the part
SHDN
on.
Fast Start-up
The EUP7982 provides fast start-up time for better
system efficiency. The start-up speed is maintained when
using the optional noise bypass capacitor.
Figure3. Adjustable LDO Regulator Programming
DS7982 Ver 1.4 May.2005
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
