MC34704 FREESCALE [Freescale Semiconductor, Inc], MC34704 Datasheet - Page 20

• Manufacturer Part Number: MC34704
• Description: Multiple Channel DC-DC Power Management IC
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

INTERNAL BIAS CIRCUIT
Gate Driver Voltage (VG)
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.
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 output starts rising. When the appropriate internal
circuitry is alive and the switching frequency F
selected, the PWM control of REG1 can take over.
VREF Generator - Internal Reference
is controlled by the I
voltage for setting the output voltage on each regulator.
20
34704
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
REG1/VG is the main regulator of the 34704 IC and will be
See Power-Up Sequence on page 27
REG1 VG starts up in peak current detect PFM mode and
Each one of the regulators in the 34704 uses a DAC which
2
C interface to generate a dynamic VREF
MC34704 - Functional Block Diagram
Startup Sequencing
Internal Bias Circuit
Fault Detection & Protection
VREF Generator
Thermal Limit
Phase Control
Over-Voltage
Fault Detection & Protection
I2C
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Figure 4. MC34704 Functional Internal Block Diagram
Internal Bias Circuit
Communication & Registers
Logic & Control
for more details on
Over-Current
SW1
is
Soft Start Control
VDDI Reference
Under-Voltage
Fault Register
Short Circuit
VDDI Reference Voltage
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
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
• A soft over-current limit (over-current limit): If the peak
The 34704 uses the internal VG voltage to provide a
There is a thermal sensor for each regulator except REG7.
The current limit circuitry has two levels of current limiting:
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
A
B
C
D
E
Output Groups
* 34704A 8-CH only
Logic & Control
Output Groups
Regulator 1*
Regulator 2
Regulator 3
Regulator 4
Regulator 5
Regulator 6*
Regulator 7*
Regulator 8
Regulator 5
Analog Integrated Circuit Device Data
Freescale Semiconductor