Ap133 – Diodes AP133 User Manual
Page 12
AP133
300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT
LOW DROPOUT LINEAR REGULATOR
AP133 Rev. 6
12 of 15
FEBRUARY 2009
©
Diodes Incorporated
Low Quiescent Current
Cellular phone baseband internal digital circuits typically
operate from 1.8V to 2.6V. When the Li+ battery voltage falls to
3.2-3.3V, most phones shut off, giving at least 500-600mV of
headroom for the baseband digital LDO, so dropout is not
critical. Output noise and the PSRR are not critical specs for
the digital circuits. Nonetheless, this supply requires low
quiescent current at light loads because this LDO stays on at
all times. Figure below shows how the digital supply current of
a representative GSM chipset core varies as a function of time.
In the standby mode, the microprocessor consumes only
around 200µA. Since the phone stays in standby for the
longest percentage of time, using a 40µA quiescent current
LDO, instead of 140µA, saves 100µA and extends the standby
time by 340µA/240µA, or 1.417 times.
The baseband internal analog circuit is typically 2.4V-3.0V, and
it requires 200-600mV dropout. This LDO is on all the time, so it
requires low quiescent current as well. The cellular phone
real-time clock LDO needs a very low quiescent current, since
this LDO is on all the time even though the handset is powered
off.
The AP133, consuming only around 40µA for all input range
and output loading, provides great power saving in portable
and low power applications.
Wide Output Range
The AP133, with a wide output range of 1.0V to 5.0V, provides
a versatile LDO solution for many portable applications.
High PSRR
The RF circuit consists of receive and transmit sections, which
typically require 2.6V-3.0V supply voltage. The RF circuits such
as LNA (low-noise amplifier), up/down-converter, mixer, PLL,
VCO, and IF stage, require low noise and high PSRR LDOs.
The temperature-compensated crystal oscillator circuit requires
very high PSRR at RF power amplifier burst frequency. For
instance, minimum 65dB PSRR at 217Hz is recommended for
the GSM handsets.
In order to provide good audio quality, the audio power supply
for hand-free, game, MP3, and multimedia applications in
cellular phones, require low-noise and high PSRR at audio
frequency range (20Hz-20kHz).
The AP133, with PSRR of 70dB at 1kHz in best case, is
suitable for some of these applications that require high PSRR.
Application Note