EUP7963
Application Note
External Capacitors
Like any low-dropout regulator, the EUP7963 requires
external capacitors for regulator stability. These
capacitors must be correctly selected for good
performance.
Flag Operation
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The EUP7963 produces a logic low signal at the
Flag pin when the output drops out of
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regulation due to low input voltage, current limiting, or
thermal limiting. This flag has a built in hysteresis.
The internal
flag comparator has an open drain
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output stage. Hence, the
Input Capacitor
pin should be pulled
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An input capacitance of 4.7µF is required between the
EUP7963 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.
high through a pull up resistor. The
pin must be
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connected to ground if this function is not used. It should
also be noted that when the shutdown pin is pulled low,
the
pin is forced to be invalid for reasons of
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saving power in shutdown mode.
Adjustable Operation
The adjustable version of the EUP7963 has an output
voltage range of 0.8V to 4.5V. The output voltage of the
EUP7963 adjustable regulator is programmed using an
external resistor divider as shown in Figure3. The output
voltage is calculated using:
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 4.7µF over the entire operating
temperature range.
R
R
1
V = V ×(1+
)
O
ref
2
Output Capacitor
Where:
The EUP7963 is designed specifically to work with very
small ceramic output capacitors. A ceramic capacitor
(temperature characteristics X7R, X5R, Z5U, or Y5V) in
10 to 22µF range with 5mΩ to 200mΩ ESR range is
suitable in the EUP7963 application circuit.
Vref= 0.8V typ. (the internal reference voltage)
Utilize the following equation for adjusting the output to
a particular voltage:
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)
V
0.8V
O
P = R
−1
I
2
Choose R2=50k to optimize accuracy, power supply
rejection, noise and power consumption.
No-Load Stability
The EUP7963 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 EUP7963 is turned off by pulling the VEN pin low,
and turned on by pulling it high. If this feature is not used,
the VEN pin should be tied to VIN to keep the regulator
output on at all time. To assure proper operation, the
signal source used to drive the VEN input must be able to
swing above and below the specified turn-on/off voltage
thresholds listed in the Electrical Characteristics section
under VIL and VIH.
DS7963 Ver 1.4 Oct. 2007
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
