Diodes AP7335A - Manual (Page 7)

AP7335A
300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT
LOW DROPOUT LINEAR REGULATOR
AP7335A
Document number: DS35267 Rev. 2 - 2
7 of 12
www.diodes.com
October 2011
© Diodes Incorporated
NEW PROD
UC
T
Application Note
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 AP7335A is stable
with very small ceramic output capacitors. Using a ceramic
capacitor value that is at least 1
μF 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
0.001
0.01
0.1
1
10
100
0 50 100 150 200 250 300
Load Current (mA)
C
OU
T
ESR
(
Ω
)
No Load Stability
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 AP7335A 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
650mA 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 160mA. 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.
Ultra Fast Start-up
After enabled, the AP7335A is able to provide full power
in as little as tens of microseconds, typically 220µs,
without sacrificing low ground current. This feature will
help load circuitry move in and out of standby mode in
real time, eventually extend battery life for mobile phones
and other portable devices.
Fast Transient Response
Fast transient response LDO can extend battery life.
TDMA-based cell phone protocols such as Global
System for Mobile Communications (GSM) have a
transmit/receive duty factor of only 12.5 percent, enabling
power savings by putting much of the baseband circuitry
into standby mode in between transmit cycles. In
baseband circuits, the load often transitions virtually
instantaneously from 100µA to 100mA. To meet this load
requirement, the LDO must react very quickly without a
large voltage drop or overshoot — a requirement that
cannot be met with conventional, general-purpose LDO.
The AP7335A’s fast transient response from 0 to 300mA
provides stable voltage supply for fast DSP and GSM
chipset with fast changing load.
Low Quiescent Current
The AP7335A, consuming only around 35µA for all input
range, provides great power saving in portable and low
power applications.
Unstable Range
Unstable Range
Stable Range
V
IN
=5.5V
C
IN
=C
OUT
=1 μF