EUP7965
Application Note
External Capacitors
Capacitor Characteristics
Like any low-dropout regulator, the EUP7965 requires
external capacitors for regulator stability. The EUP7965
is specifically designed for portable applications
requiring minimum board space and smallest components.
These capacitors must be correctly selected for good
performance.
The EUP7965 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 EUP7965.
Input Capacitor
An input capacitance of 1µF is required between the
≈
EUP7965 input pin and ground (the amount of the
capacitance may be increased without limit).
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
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.
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.
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
Noise Bypass Capacitor
Connecting a 0.01µF capacitor between the CBYPASS pin
and ground significantly reduces noise on the regulator
output. This cap is connected directly to a high
impedance node in the bandgap reference circuit. Any
significant loading on this node will cause a change on
the regulated output voltage. For this reason, DC leakage
current through this pin must be kept as low as possible
for best output voltage accuracy. The types of capacitors
best suited for the noise bypass capacitor are ceramic and
film.
capacitance will be 1µF over the entire operating
≈
temperature range.
Output Capacitor
The EUP7965 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 EUP7965 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)
Unlike many other LDO’s , addition of a noise reduction
capacitor does not effect the load transient response of
the device.
On/Off Input Operation
No-Load Stability
The EUP7965 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.
The EUP7965 will remain stable and in regulation with
no external load. This is specially important in CMOS
RAM keep-alive applications.
Fast Start up
The EUP7965 output starts up after Vref voltage reaches
its final value (1.23V nomial). The start-up time is
determined by the time constant of the bypass capacitor.
The smaller the capacitor value., the shorter the start-up
time, but less noise gets reduced. As a result, start-up
time and noise reduction need to be taken into design
consideration when choosing the value of the bypass
capacitor.
DS7965 Ver1.5 March. 2006
12
EUTECH [ EUTECH MICROELECTRONICS INC ]
