EUP7961
Application Note
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 very close to the input pin and
returned to a clean analog ground. Any good quality
ceramic, tantalum, or film capacitor can 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 small
ceramic output capacitors. A ceramic capacitor
(temperature characteristics X7R, X5R, Z5U, or Y5V) in
4.7µF 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 4.7µF over the entire operating range 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 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
ERROR
is an open drain output. 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. In shutdown, the
ERROR
pin is Hi-Z state to save input power.
voltage is calculated using:
V
=
V
O
ref
×
(1
+
R
R
1
)
2
Where:
Vref= 0.8V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
V
P
I
=
R
O
−
1
2
0.8V
Choose R
2
=50k to optimize accuracy, power supply
rejection, noise and power consumption.
Power Dissipation
EUP7961 can deliver a continuous current of 2A over the
full operating temperature range. A heatsink may be
required depending on the maximum power dissipation
and maximum ambient temperature of the application.
Under all possible conditions, the junction temperature
must be within the range specified under operating
conditions. The total power dissipation of the device is
given by:
P
=
V
−
V
I
+
V
I
D
IN
IN GND
OUT OUT
(
)
( )
Where I
GND
is the operating ground current of the device
(specified under Electrical Characteristics).
The maximum allowable temperature rise (T
Rmax
)
depends on the maximum ambient temperature (T
Amax
)
of the application, and the maximum allowable junction
temperature (T
Jmax
):
T
Rmax
= T
Jmax
-T
Amax
The maximum allowable value for junction to ambient
Thermal Resistance,
θ
JA
, can be calculated using the
formula:
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
DS7961
Ver 1.4
Jan. 2009
θ
JA
=T
Rmax
/P
D
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
