AP7312
DUAL 150mA LOW QUIESCENT CURRENT FAST
TRANSIENT LOW DROPOUT LINEAR REGULATOR
AP7312
Document number: DS35133 Rev. 2 - 2
13 of 18
www.diodes.com
January 2011
© Diodes Incorporated
NEW PRODUCT
Application Note (Continued)
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 300mA 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
60mA. 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 +165°C, allowing the device to
cool down. When the junction temperature reduces to approximately +135°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 AP7312 is able to provide full power in as little as tens of microseconds, typically 150µs, 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 AP7312’s fast transient response from 0 to 150mA provides stable voltage supply for fast DSP and GSM chipset with
fast changing load.
Low Quiescent Current
The AP7312, consuming only around 60µA for all input range, provides great power saving in portable and low power
applications.
Power Dissipation
The device power dissipation and proper sizing of the thermal plane that is connected to the thermal pad is critical to avoid
thermal shutdown and ensure reliable operation. Power dissipation of the device depends on input voltage and load
conditions and can be calculated by:
P
D
= (V
IN
- V
OUT
) X I
OUT
The maximum power dissipation, handled by the device, depends on the maximum junction to ambient thermal resistance,
maximum ambient temperature, and maximum device junction temperature, which can be calculated by the equation in the
following:
P
D
(max@T
A
) =
JA
R
)
A
T-C150(
θ
°
