Diodes AP7165 - Manual (Page 9)

AP7165
600mA LOW DROPOUT REGULATOR WITH POK
AP7165
Document number: DS31270 Rev. 7 - 2
9 of 15
www.diodes.com
March 2012
© Diodes Incorporated
Application Notes
Input Capacitor
A 1µF ceramic capacitor is recommended to connect
between IN and GND pins to decouple input power supply
glitch and noise. The amount of the capacitance may be
increased without limit. A lower ESR (Equivalent Series
Resistance) capacitor allows the use of less capacitance,
while higher ESR type requires more capacitance. This
input capacitor should be located as close as possible to
the device to assure input stability and less noise. For PCB
layout, a wide copper trace is required for both IN and
GND.
Output Capacitor
The output capacitor is required to stabilize and help the
transient response of the LDO. The AP7165 is designed to
have excellent transient response for most applications with
a small amount of output capacitance. The AP7165 is
stable for all available types and values of output capacitors
≥ 4.7μF. The device is also stable with multiple capacitors
in parallel, which can be of any type of value. Additional
capacitance helps to reduce undershoot and overshoot
during transient. This capacitor should be placed as close
as possible to OUT and GND pins for optimum
performance.
Adjustable Operation
The AP7165 provides output voltage from 0.8V to 5.0V
through external resistor divider as shown below.
IN
GND EN
OUT
Enable
FB
V
IN
V
OUT
POK
100kOhm
R
1
R
2
AP7165
C
IN
C
OUT
The output voltage is calculated by:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+ =
2
1
REF OUT
R
R
1 V V
Where V
REF
= 0.8V (the internal reference voltage).
Rearranging the equation will give the following equation
to find the approximate resistor divider values:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
− =
1
V
V
R R
REF
OUT
2 1
To maintain the stability of the internal reference voltage,
R
2
needs to be kept smaller than 250k
Ω.
No Load Stability
Other than external resistor divider, no minimum load is
required to keep the device stable. The device will remain
stable and regulated in no load condition.
ENABLE/SHUTDOWN Operation
The AP7165 is turned on by setting the EN pin high, and is
turned off by pulling it low. If this feature is not used, the
EN pin should be tied to IN pin to keep the regulator
output on at all time. To ensure proper operation, the
signal source used to drive the EN pin must be able to
swing above and below the specified turn-on/off voltage
thresholds listed in the Electrical Characteristics section
under V
IL
and V
IH
.
POWER-OK
The Power-Ok (POK) pin is an active high open-drain
output. It can be connected to any 5.5V or lower rail
through an external pull-up resistor. The recommended
sink current of POK pin is up to 4mA, so the pull-up
resistor for POK should be in the range of 10k
Ω to 1MΩ. If
output voltage monitoring is not needed, the POK pin can
be left floating.
Current Limit Protection
When output current at OUT pin is higher than current limit
threshold, the current limit protection will be triggered and
clamp the output current to approximately 950mA (600A
min) to prevent over-current and to protect the regulator
from damage due to overheating.
Short Circuit Protection
When OUT pin is short-circuited to GND or OUT pin
voltage is less than 200mV, short circuit protection will be
triggered and clamp the output current to approximately
380mA. This feature protects the regulator from over-
current and damage due to overheating.