34704_09 Datasheet, PDF (22/49 Pages) Freescale Semiconductor, Inc – Multiple Channel DC-DC Power Management IC

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
(>5.0V) 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 5.2V and not allow it to drift all the way to 5.5V.
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 F_SW1
• Drives integrated low R_DS(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 5.0V 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 27 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 F_SW1
• Drives integrated low R_DS(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.
See Power-Up Sequence on page 27 for more details on
when REG3 is powered up in the sequence.
34704
22
Analog Integrated Circuit Device Data
Freescale Semiconductor