AP7335_1009 Datasheet, PDF (11/17 Pages) Diodes Incorporated – 300mA, Low Quiescent Current, Fast Transient

AP7335
300mA, Low Quiescent Current, Fast Transient
Low Dropout Linear Regulator
Application Note
Input Capacitor
A 1μF ceramic capacitor is recommended between IN and
GND pins to decouple input power supply glitch and noise.
The amount of the capacitance may be increased without
limit. This input capacitor must be located as close as
possible to the device to assure input stability and reduce
noise. For PCB layout, a wide copper trace is required for
both IN and GND pins. A lower ESR capacitor type allows
the use of less capacitance, while higher ESR type
requires more capacitance.
Output Capacitor
The output capacitor is required to stabilize and improve
the transient response of the LDO. The AP7335 is stable
with very small ceramic output capacitors. Using a ceramic
capacitor value that is at least 1μF with ESR > 15mΩ on
the output ensures stability. Higher capacitance values
help to improve line and load transient response. The
output capacitance may be increased to keep low
undershoot and overshoot. Output capacitor must be
placed as close as possible to OUT and GND pins.
Region of Stable C_OUT ESR vs. Load Current
100
Unstable Range
10
1
Stable
R
0.1
V_IN=4.3V
C_IN=C_OUT=1μF
0.01
0.001
0
Unstable Range
50 100 150 200 250 300
Load Current (mA)
Adjustable Operation
The AP7335 provides output voltage from 0.8V to 5.0V
through external resistor divider as shown below.
The output voltage is calculated by:
VOUT
=
VREF _{⎜⎜⎝⎛}1 +
R1
R2
⎟⎟⎠⎞
Where V_REF=0.8V (the internal reference voltage)
Rearranging the equation will give the following that is
used for adjusting the output to a particular voltage:
R1
=
R2_{⎜⎜⎝⎛}
VOUT
VREF
− 1_{⎟⎟⎠⎞}
To maintain the stability of the internal reference voltage,
R₂ need to be kept smaller than 80kΩ.
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.
ON/OFF Input Operation
The AP7335 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.
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 600mA to
prevent over-current and to protect the regulator from
damage due to overheating.
Short Circuit Protection
When OUT pin is short-circuit to GND, short circuit
protection will be triggered and clamp the output current to
approximately 140mA. This feature protects the regulator
from over-current and damage due to overheating.
V _IN
IN
OUT
AP7335
R1
1uF
Enable _EN
ADJ
GND
R2
V_OUT
1uF
Thermal Shutdown Protection
Thermal protection disables the output when the junction
temperature rises to approximately +145°C, allowing the
device to cool down. When the junction temperature
reduces to approximately +130°C the output circuitry is
enabled again. Depending on power dissipation,
thermal resistance, and ambient temperature, the
thermal protection circuit may cycle on and off.
This cycling limits the heat dissipation of the regulator,
protecting it from damage due to overheating.
AP7335
Document number: DS32259 Rev. 2 - 2
11 of 17
www.diodes.com
September 2010
© Diodes Incorporated