EUP7987
Shutdown
Adjustable Operation
The EUP7987 goes into sleep mode when the
SHDN
The adjustable version of the EUP7987 has an output
voltage range of 1.25V to 6V. The output voltage of the
EUP7987 adjustable regulator is programmed using an
external resistor divider as shown in Figure3. The output
voltage is calculated using:
pin 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
pin may be directly tied to VIN to keep the part
SHDN
on.
R
1
V = V ×(1+
)
O
ref
R
2
Fast Start-up
Where:
The EUP7987 provides fast start-up time for better
system efficiency. The start-up speed is maintained when
using the optional noise bypass capacitor.
Vref=1.23V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
V
O
P = R
−1
I
2
1.23V
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 VOUT and SET
DS7987 Ver 1.5 May .2005
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
