EUP7961
Application Note
External Capacitors
Like any low-dropout regulator, the EUP7961 requires
external capacitors for regulator stability. These
capacitors must be correctly selected for good
performance.
Input Capacitor
An input capacitance of 1µF is required between the
EUP7961 input pin and ground (the amount of the
capacitance may be increased without limit).
This capacitor must be located a distance of not more
than 1cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or
film capacitor may be used at the input.
If a tantalum capacitor is used at the input, it must be
guaranteed by the manufacturer to have a surge current
rating sufficient for the application.
There are no requirements for the ESR on the input
capacitor, but tolerance and temperature coefficient must
be considered when selecting the capacitor to ensure the
capacitance will be 1µF over the entire operating
temperature range.
Output Capacitor
The EUP7961 is designed specifically to work with very
small ceramic output capacitors. A ceramic capacitor
(temperature characteristics X7R, X5R, Z5U, or Y5V) in
4.7 to 22µF range with 5mΩ to 200mΩ ESR range is
suitable in the EUP7961 application circuit.
The output capacitor must meet the requirement for
minimum amount of capacitance and also have an ESR
(Equivalent Series Resistance) value which is within a
stable range (5mΩ to 200mΩ)
No-Load Stability
The EUP7961 will remain stable and in regulation with
no external load. This is specially important in CMOS
RAM keep-alive applications.
On/Off Input Operation
The EUP7961 is turned off by pulling the V
EN
pin low,
and turned on by pulling it high. If this feature is not used,
the V
EN
pin should be tied to V
IN
to keep the regulator
output on at all time. To assure proper operation, the
signal source used to drive the V
EN
input must be able
to swing above and below the specified turn-on/off
voltage thresholds listed in the Electrical Characteristics
section under V
IL
and V
IH
.
ERROR
Flag Operation
The EUP7961 produces a logic low signal at the
ERROR
Flag pin when the output drops out of
regulation due to low input voltage, current limiting, or
thermal limiting. This flag has a built in hysteresis.
The internal
ERROR
flag comparator has an open drain
output stage. Hence, the
ERROR
pin should be pulled
high through a pull up resistor. The
ERROR
pin must be
connected to ground if this function is not used. It should
also be noted that when the shutdown pin is pulled low,
the
ERROR
pin is forced to be invalid for reasons of
saving power in shutdown mode.
Adjustable Operation
The adjustable version of the EUP7961 has an output
voltage range of 0.8V to 4.5V. The output voltage of the
EUP7961 adjustable regulator is programmed using an
external resistor divider as shown in Figure3. The output
voltage is calculated using:
V
=
V
O
ref
×
(1
+
R
1
R
2
)
Where:
Vref= 0.8V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
V
O
P
I
=
R
−
1
2
0.8V
Choose R
2
=50k to optimize accuracy, power supply
rejection, noise and power consumption.
DS7961 Ver 1.2 Dec. 2006
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
