AP7335 Datasheet, PDF (13/18 Pages) Diodes Incorporated – 300mA, Low Quiescent Current, Fast Transient Low Dropout Linear Regulator

AP7335
300mA, Low Quiescent Current, Fast Transient
Low Dropout Linear Regulator
Application Note (Continued)
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 AP7335 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 AP7335’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 AP7335, consuming only around 35µA for all input range, provides great power saving in portable and low
power applications.
Wide Output Range
The AP7335, with a wide output range of 0.8V to 5.0V, provides a versatile LDO solution for many portable
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)
=
(+145°C -
R _θJA
TA
)
AP7335
Document number: DS32259 Rev. 1 - 2
13 of 18
www.diodes.com
July 2010
© Diodes Incorporated