Diodes AP7335 - Manual (Page 10)

AP7335
300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT
LOW DROPOUT LINEAR REGULATOR
AP7335
Document number: DS32259 Rev. 3 - 2
10 of 16
www.diodes.com
December 2011
© Diodes Incorporated
NEW PROD
UC
T
Application Notes
Input Capacitor
A 1 μF 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 1
μF with ESR >
15m Ω 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.
Adjustable Operation
The AP7335 provides output voltage from 0.8V to 5.0V
through external resistor divider as shown below.
1 u F
IN
G N D
E N
O U T
E n a b le
A D J
R 2
R 1
1 u F
V
IN V
O U T
A P 7 3 3 5
The output voltage is calculated by:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+ =
2 R
1
R
1 REF V OUT V
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:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
− =
1
REF V
OUT
V
2 R 1 R
To maintain the stability of the internal reference voltage,
R
2
need to be kept smaller than 80k
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.
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.
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.
Unstable Range
Stable
Unstable Range
V = 4.3V
C = C = 1µF
IN
IN OUT
LOAD CURRENT (mA)
Region of Stable C ESR vs. Load Current
OUT
0 50 100 150 200 250 300
0.001
0.01
0.1
1
10
100
C E
S
R
(
)
OU
T
Ω