FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
REGUALATOR OVERVIEW WITH EFFICIENCY ANALYSIS
REG1 (34704A Only)
• There is no ALLOFF shutdown command through the I2C
interface AND
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
• No faults exist that would cause the 34704 to shutdown
The VOUT1 output will be active when:
• VG output is available AND
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.
• 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.
The switcher will operate in DCM at very light loads to
allow pulse skipping.
See Power-Up Sequence on page 28 for more details on
when REG2 is powered up in the sequence.
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.
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.
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
Characteristics
• It powers up directly from the battery
• It powers up directly from the battery
• Operates at a switching frequency equals to FSW1
• Operates at a switching frequency equals to FSW1
• Drives integrated low RDS(ON) N-channel power
MOSFETs (NHV_HC) as its output stage
• Drives integrated low RDS(ON) N-channel power
MOSFETs (NHV_HC) as its output stage
• The output is ±2% accuracy
• It offers load disconnect from the input battery when the
output is off (True Cutoff)
• Output voltage is adjustable by means of an external
resistor divider
• The output is ±4% accuracy
• 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
• 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 bootstrap networks with an internal diode to power
its high side MOSFETs
• All gate drive circuits are supplied from VG
• Uses external compensation
• Uses a bootstrap network with an internal diode to power
its synchronous MOSFET
• The output is monitored for under-voltage and over-
voltage conditions
• All gate drive circuits are supplied from REG1’s own VG
output.
• The output is monitored for over-current and short-circuit
conditions
• Uses integrated compensation
• The output is monitored for under-voltage and over-
voltage conditions
• The regulator is monitored for over-temperature conditions
• The output is monitored for over-current and short-circuit
conditions
Operation Modes
The switcher will be active when:
• VG is in regulation AND
• The regulator is monitored for over-temperature conditions
• There is no GrpB shutdown command through the I2C
interface AND
Operation Modes
The VG output is always active as long as:
• No faults exist that would cause GrpB to shut down
• The IC is not in an under-voltage lockout AND
• No shutdown signal through the ONOFF pin is present
AND
REG3
This is a synchronous buck PWM voltage-mode control
DC/DC regulator.
34704
Analog Integrated Circuit Device Data
Freescale Semiconductor
22
FREESCALE [ Freescale ]
