900844 Datasheet, PDF (58/118 Pages) Freescale Semiconductor, Inc – Integrated Power Management IC for Ultra-mobile and Embedded Applications

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/R_W, then the voltage
across the capacitor is equal to the value of the voltage across the winding resistance R_W, V_CAP = I_LOAD*R_W. Based on this, the
voltage across the capacitor is measured, and with a known R_W 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 R_W 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.
VCC
COCC
VPWR
CINCC
LCC
PVINCC
HSCCGT
MHSCC
MLSCC _LSCCGT
PGNDCC
SWFBCC
CSPCC
VOUTFBCC
GNDREFVCC
Driver
Controller
CTLVCC
AOACCTLVCC
Current Sense
Amp
ICC
Internal
Compensation _Z2
Z1
EA
VCCFAULT
SPI
Interface
DAC
VREF
VIDEN0
VIDEN1
Figure 23. VCC Detailed Internal Block Diagram
Main Features
• Uses the V_PWR 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.
900844
58
Analog Integrated Circuit Device Data
Freescale Semiconductor