900844 datasheet(58/118 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

900844

FUNCTIONAL DEVICE OPERATION

POWER SUPPLIES

The switcher can operate in different modes depending on the load conditions. These modes can be set through the SPI and

include a PFM mode, an Automatic Pulse Skipping mode, and a PWM mode. The above selection is optimized to maximum

battery life based on load conditions.

VCC will be discharged every time the regulator is shutting down.

The output current will be sensed using an intelligent implementation of the DCR sensing method using internal sensing

circuitry, which eliminates the need for an external RC filter network in parallel with the output inductor and its winding resistance.

DCR sensing theory is that if the impedance of the two filters are matching by insuring that R*C = L/RW, then the voltage

across the capacitor is equal to the value of the voltage across the winding resistance RW, VCAP = ILOAD*RW. Based on this, the

voltage across the capacitor is measured, and with a known RW value, the load current can be extracted. The measured current

value will be digitized by the ADC and stored in a register for the processor to access. The method used on the 900844 measures

the voltage across RW in a similar fashion, while using internal sensing circuitry.

The sensed output current value will also be used for over-current protection. If an over-current condition is detected, the

regulator will limit the current through cycle by cycle operation, and alert the system through the VCCFAULT signal, which will in

turn assert the VRFAULT Interrupt signal.

Figure 23. VCC Detailed Internal Block Diagram

Main Features

• Uses the VPWR rail as its power supply

• It is used to provide power to the CPU Core.

• Single-phase Solution with Integrated Drivers and external MOSFETs

• VID Controlled for dynamic voltage scaling requirements of high performance processors

•1.0 MHz switching frequency

• High efficiency operating modes depending on load conditions

• Output can be discharged through the low side switch.

• Loss-Less Output Current Sensing with over-current protection

• Uses internal compensation

• Gate drive circuits are supplied directly from VPWR

Efficiency Curves

The efficiency curves in Figure 24 are calculated under PWM mode, based on the recommended external component values

and typical output voltage of 1.2 V. 3.0 V

≤ VPWR ≤ 4.4 V.

GNDREFVCC

Driver

Controller

Internal

Compensation

VOUTFBCC

VPWR

COCC

CINCC

LCC

VCC

HSCCGT

LSCCGT

PGNDCC

Current Sense

Amp

CSPCC

ICC

PVINCC

SWFBCC

SPI

Interface

CTLVCC

AOACCTLVCC

VCCFAULT

VREF

DAC

MHSCC

MLSCC

VIDEN0

VIDEN1

900844 Datasheet(PDF) 58 Page - Freescale Semiconductor, Inc

900844 Datasheet(HTML) 58 Page - Freescale Semiconductor, Inc

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