EUP7967A
Application Information
External Capacitors
Like any low-dropout regulator, the EUP7967A requires
external capacitors for regulator stability. The EUP7967A
is specifically designed for portable applications
requiring minimum board space and smallest components.
These capacitors must be correctly selected for good
performance.
Input Capacitor
Noise Bypass Capacitor
An external 10nF bypass capacitor at BP pin conjunction
with an internal resistor creates lowpass filter. Increasing
the capacitance will decrease the output noise. 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.
Unlike many other LDO’s , addition of a noise reduction
capacitor does not effect the load transient response of
the device. However, it does affect start-up time. The
smaller the capacitance value, the quicker the start-up
time.
Power Dissipation and Junction Temperature
A minimum input capacitance of 1µF is required between
the EUP7967A 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.
No-Load Stability
The EUP7967A will remain stable and in regulation with
no external load. This is specially important in CMOS
RAM keep-alive applications.
Output Capacitance
The EUP7967A is specifically designed to employ
ceramic output capacitors as low as 2.2µF. Ceramic
capacitors below 10µF offer significant cost and space
savings, along with high frequency noise filtering. Higher
values and other types and of capacitor may be used, but
their equivalent series resistance (ESR) should be
maintained below 0.5Ω. Ceramic capacitor of the value
required by the EUP7967A are available in the following
dielectric types: Z5U, Y5V, X5R, and X7R. The Z5U and
Y5V types exhibit a 50% or more drop in capacitance
value as their temperature increase from 25°C, an
important consideration. The X5R generally maintain
their capacitance value within ± 20%. The X7R type are
desirable for their tighter tolerance of 10% over
temperature.
Specified regulator operation is assured to a junction
temperature of 125°C; the maximum junction
temperature should be restricted to 125°C under normal
operating conditions. This restriction limits the power
dissipation the regulator can handle in any given
application. To ensure the junction temperature is within
acceptable limits, calculate the maximum allowable
dissipation, P
D(max)
, and the actual dissipation, P
D
, which
must be less than or equal to P
D(max)
The maximum-power-dissipation limit is determined
using the following equation:
P
T max
−
T
A
=
J
D(max)
R
θJA
Where:
T
JMAX
is the maximum allowable junction temperature.
R
θJA
is the thermal resistance junction-to-ambient for the
package
T
A
is the ambient temperature.
The regulator dissipation is calculated using:
PD
=
VI
−
VO
×
I O
(
)
Power dissipation resulting from quiescent current is
negligible. Excessive power dissipation triggers the
thermal protection circuit.
Shutdown
The EUP7967A goes into sleep mode when the
SHDN
pin is in a logic low condition. During this condition, the
pass transistor, error amplifier, and bandgap are turned
off, reducing the supply current to 60nA typical. The
SHDN
pin may be directly tied to V
IN
to keep the part
on.
DS7967A Ver 1.4
Sep. 2007
7
EUTECH [ EUTECH MICROELECTRONICS INC ]
