EUP7201
Application Note
External Capacitors
Capacitor Characteristics
Like any low-dropout regulator, the EUP7201 requires
external capacitors for regulator stability. The EUP7201 is
specifically designed for portable applications requiring
minimum board space and smallest components. These
capacitors must be correctly selected for good
performance.
The EUP7201 is designed to work with ceramic
capacitors on the output to take advantage of the benefits
they offer: for capacitance values in the range of 1µF to
4.7µF range, ceramic capacitors are the smallest, least
expensive and have the lowest ESR values (which makes
them best for eliminating high frequency noise). The
ESR of a typical 1µF ceramic capacitor is in the range of
20mΩ to 40mΩ, which easily meets the ESR requirement
for stability by the EUP7201.
The ceramic capacitor’s capacitance can vary with
temperature. The capacitor type X7R, which operates
over a temperature range of -55°C to +125°C, will only
vary the capacitance to within ±15%. Most large value
ceramic capacitors (≈2.2µF) are manufactured with Z5U
or Y5V temperature characteristics. Their capacitance
can drop by more than 50% as the temperature goes from
25°C to 85°C. Therefore, X7R is recommended over Z5U
and Y5V in applications where the ambient temperature
will change significantly above or below 25°C.
Input Capacitor
An input capacitance of ≈1µF is required between the
EUP7201 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
On/Off Input Operation
capacitance will be 1µF over the entire operating
≈
The EUP7201 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.
temperature range.
Output Capacitor
The EUP7201 is designed specifically to work with very
small ceramic output capacitors. A ceramic capacitor
(temperature characteristics X7R, X5R, Z5U, or Y5V) in 1
to 22µF range with 5mΩ to 500mΩ ESR range is suitable
in the EUP7201 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 500mΩ)
No-Load Stability
The EUP7201 will remain stable and in regulation with no
external load. This is specially important in CMOS RAM
keep-alive applications.
DS7201 Ver 1.6 Sep. 2008
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
