EUP7987
Adjustable Operation
Shutdown
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:
R
V
=
V
×
(1
+
1
)
O
ref
R
2
The EUP7987 goes into sleep mode when the
SHDN
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
SHDN
pin may be directly tied to V
IN
to keep the part
on.
Fast Start-up
Where:
Vref=1.23V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
V
O
P
I
=
R
2
−
1
1.23V
Choose R
2
=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 C
1
be
placed between V
OUT
and SET
The EUP7987 provides fast start-up time for better
system efficiency. The start-up speed is maintained when
using the optional noise bypass capacitor.
DS7987 Ver 1.5 May .2005
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
