34704_11 Datasheet, PDF (25/54 Pages) Freescale Semiconductor, Inc – Multiple Channel DC-DC Power Management IC

FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
• Operates at a switching frequency equals to F_SW2
• Drives integrated low R_DS(ON) N-channel power
MOSFETs (NVHV_LC) as its output stage
• It offers load disconnect from the input battery when the
output is off (True Cut-Off)
• The output is ±4% accuracy
• Output voltage is adjustable by means of an external
resistor divider when in voltage regulation mode
• A 240 mV current limit comparator will be used to program/
sense the voltage drop across the current setting resistor
at the bottom of the LED string connected to the REG8
output when the current regulation mode is selected.
This will be used to program the maximum current flowing
and will regulate it
• The output can be adjusted up or down at 2.5% steps for
a total of 10% on each direction allowing Dynamic Voltage
Scaling
• Maximum output current is adjustable by means of an
external resistor connected to the FB8 pin and then the
output current can be scaled down from the set maximum
in 16 steps through I²C interface
• Uses a bootstrap network with an internal diode to power
its synchronous MOSFET
• All gate drive circuits are supplied from VG.
• Uses integrated compensation
• The output is monitored for over-current and short-circuit
conditions
• The regulator is monitored for over-temperature conditions
• The output is monitored for under-voltage and over-
voltage conditions
Operation Modes
The switchers will be active when:
• VG is in regulation AND
• There is no GrpD shutdown command through the I²C
interface AND
• No faults exist that would cause GrpD to shut down
OVERALL EFFICIENCY ANALYSIS
In battery applications, it is highly recommended to power
every single regulator directly from the battery to obtain full
output capability:
VBAT
REG1
V1 (5.0 V)
VBAT
REG2
V2 (2.8 / 3.3 V)
VBAT
REG3
V3 (1.2 V / 1.5 V / 1.8 V)
VBAT
REG4
V4 (1.8 V / 2.5 V)
VBAT
REG5
V5 (3.3 V)
VBAT
REG6
V6 (15 V)
VBAT
REG7
V7 (-7.0 V)
VBAT
REG8
V8 (15 V)
Figure 5. Overall Efficiency Analysis
Efficiency analysis includes the following losses:
• MOSFET Conduction Losses
• MOSFET Switching Losses (Except for REG7 due to
external MOSFET and board layout dependence)
• MOSFET Gate Charging Losses
• MOSFET Deadtime Losses
• External Diode Losses (Only for REG7)
• Inductor Winding DC Losses
• Inductor Core Losses (Assumed to be 20% of DC Losses
as a rule of thumb)
• Output AC Losses
Efficiency Analysis
In this configuration, all of the regulators are supplied or
powered directly with 3.6 V nominal, battery voltage.
Efficiency was calculated using the maximum allowed
frequency of 1.5 MHz and 1.0 MHz for F_SW1 and F_SW2,
respectively, in this configuration. As a result, the following
numbers are valid for worst case operation conditions.
The following table shows the detailed analysis for each
regulator with V2 at 3.3 V, V3 at 1.2 V, and V4 at 1.8 V.
Analog Integrated Circuit Device Data
Freescale Semiconductor
34704
25