34704_09 Datasheet, PDF (20/49 Pages) Freescale Semiconductor, Inc – Multiple Channel DC-DC Power Management IC

FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34704 - Functional Block Diagram
Internal Bias Circuit
VREF Generator
VDDI Reference
Gate Driver Voltage VG
Fault Detection & Protection
Over-Voltage
Under-Voltage
Thermal Limit
Short Circuit
Over-Current
Output Groups
A Regulator 1*
Regulator 2
B ^{Regulator 3}
Regulator 4
Regulator 5
C ^{Regulator 6*}
Regulator 7*
Logic & Control
Startup Sequencing Soft Start Control
Phase Control
Fault Register
I2C Communication & Registers
Internal Bias Circuit
Fault Detection & Protection
D ^{Regulator 8}
E ^{Regulator 5}
* 34704A 8-CH only
Logic & Control
Output Groups
Figure 4. MC34704 Functional Internal Block Diagram
INTERNAL BIAS CIRCUIT
Gate Driver Voltage (VG)
REG1/VG is the main regulator of the 34704 IC and will be
used to supply internal circuitry and voltage biases through
the VG output. It also provides the gate drive voltage for the
rest of the regulators and itself.
See Power-Up Sequence on page 27 for more details on
how REG1 is a critical part of powering up the 34704. Based
on this, REG1 will need extra circuitry to help it boot up until
its output voltage is high enough that it can supply internal
circuitry for the main control loop to take over.
REG1 VG starts up in peak current detect PFM mode and
REG1 VG output starts rising. When the appropriate internal
circuitry is alive and the switching frequency F_SW1 is
selected, the PWM control of REG1 can take over.
VREF Generator - Internal Reference
Each one of the regulators in the 34704 uses a DAC which
is controlled by the I²C interface to generate a dynamic VREF
voltage for setting the output voltage on each regulator.
VDDI Reference Voltage
The 34704 uses the internal VG voltage to provide a
precise low current 2.5V voltage that is meant to serve as
reference voltage to derive the FREQ and SS voltage needed
to set the switching frequency 1 (FSW1) and the soft start,
respectively.
FAULT DETECTION AND PROTECTION
Thermal Limit Detection
There is a thermal sensor for each regulator except REG7.
All regulators of the corresponding group will shutdown if at
least one of them reaches the thermal limit. If either REG2,
REG3 or REG4 reaches its thermal limit, the whole part will
shutdown immediately.
Over-Current & Short Circuit Monitoring
The current limit circuitry has two levels of current limiting:
• A soft over-current limit (over-current limit): If the peak
current reaches the typical over-current limit, the switcher
will start a cycle-by-cycle operation to limit the current and
a 10ms current limit timer starts. The switcher will stay in
this mode of operation until the part regains normal
34704
20
Analog Integrated Circuit Device Data
Freescale Semiconductor