Diodes AP133 Manuel d'utilisateur télécharger pdf (Page 12)

AP133

300mA, LOW QUIESCENT CURRENT, FAST TRANSIENT

LOW DROPOUT LINEAR REGULATOR

AP133 Rev. 6 12 of 15 FEBRUARY 2009

www.diodes.com © 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

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Diodes AP133 Manuel d'utilisateur Page 12

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