34704 datasheet(22/54 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34704

FUNCTIONAL DESCRIPTION

FUNCTIONAL INTERNAL BLOCK DESCRIPTION

REGUALATOR OVERVIEW WITH EFFICIENCY ANALYSIS

REG1 (34704A Only)

REG1 is a synchronous boost PWM voltage-mode control

DC/DC regulator available only in the 34704A. Even though

REG1 is a synchronous regulator, it is recommended to have

a diode connected externally across its synchronous

MOSFET. When the battery voltage is above REG1’s output

(>5.0 V) as the case might be when connected to the USB

supply or wall adaptor, the REG1 power MOSFETs will be tri-

stated and the voltage on the output will be Battery minus the

diode drop. This will help maintain REG1’s output to a

maximum of 5.2 V and not allow it to drift all the way to 5.5 V.

The switcher will operate in DCM at very light loads to

allow pulse skipping.

On the 34704A, when the appropriate command is

received from the processor to turn on VOUT1, then the

isolation FET of REG1 would turn on gradually to avoid any

inrush current out of VG and to ramp the VOUT1 voltage in a

controlled manner.

REG1 VOUT1 will be discharged every time GrpA is

shutting down and it will be held low by the discharge FET as

long as possible.

Characteristics

• It powers up directly from the battery

• Operates at a switching frequency equals to FSW1

• Drives integrated low RDS(ON) N-channel power

MOSFETs (NHV_HC) as its output stage

• It offers load disconnect from the input battery when the

output is off (True Cutoff)

• The output is ±4% accuracy

• Output voltage is set to 5.0 V by means of an internal

resistor divider

• The output can be adjusted up or down at 2.5% for a total

of 10% on each direction allowing Dynamic Voltage

Scaling

• Uses a bootstrap network with an internal diode to power

its synchronous MOSFET

• All gate drive circuits are supplied from REG1’s own VG

output.

• Uses integrated compensation

• The output is monitored for under-voltage and over-

voltage conditions

• The output is monitored for over-current and short-circuit

conditions

• The regulator is monitored for over-temperature conditions

Operation Modes

The VG output is always active as long as:

• The IC is not in an under-voltage lockout AND

• No shutdown signal through the ONOFF pin is present

AND

• There is no ALLOFF shutdown command through the I2C

interface AND

• No faults exist that would cause the 34704 to shutdown

The VOUT1 output will be active when:

• VG output is available AND

• There is no GrpA shutdown command through the I2C

interface AND

• No faults exist that would cause the VOUT1 to shut down

REG2

This is a 4-switch synchronous buck-boost PWM voltage-

mode control DC/DC regulator.

See Power-Up Sequence on page 28 for more details on

when REG2 is powered up in the sequence.

The switcher will operate in DCM at very light loads to

allow pulse skipping.

VOUT2 will be discharged every time the regulator is

shutting down and it will be held low by the discharge FET as

long as possible.

Characteristics

• It powers up directly from the battery

• Operates at a switching frequency equals to FSW1

• Drives integrated low RDS(ON) N-channel power

MOSFETs (NHV_HC) as its output stage

• The output is ±2% accuracy

• Output voltage is adjustable by means of an external

resistor divider

• The output can be adjusted up or down at 2.5% steps for

a total of +17.5% to -20.0% on each direction allowing

Dynamic Voltage Scaling

• Uses bootstrap networks with an internal diode to power

its high side MOSFETs

• All gate drive circuits are supplied from VG

• Uses external compensation

• The output is monitored for under-voltage and over-

voltage conditions

• The output is monitored for over-current and short-circuit

conditions

• The regulator is monitored for over-temperature conditions

Operation Modes

The switcher will be active when:

• VG is in regulation AND

• There is no GrpB shutdown command through the I2C

interface AND

• No faults exist that would cause GrpB to shut down

REG3

This is a synchronous buck PWM voltage-mode control

DC/DC regulator.

34704 Datasheet(PDF) 22 Page - Freescale Semiconductor, Inc

34704 Datasheet(HTML) 22 Page - Freescale Semiconductor, Inc

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