34704_09 Datasheet, PDF (33/49 Pages) Freescale Semiconductor, Inc – Multiple Channel DC-DC Power Management IC

FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
SCF
bit
False
0
True
1
Over-voltage Fault Register
The 34704 assigns a 1-bit register for each regulator
(OVFx Register) to indicate a fault due to over-voltage limit,
where x corresponds to each regulator from REG1 to REG8
OVF
bit
False
0
True
1
Under-voltage Fault Register
The 34704 assigns a 1-bit register for each regulator
(UVFx Register) to indicate a fault due to under-voltage limit,
where x corresponds to each regulator from REG1 to REG8.
UVF
bit
False
0
True
1
Thermal Shutdown Fault Register
The 34704 assigns a 1-bit register for each regulator
(TSDFx Register) to indicate a fault due to thermal limit,
where x corresponds to each regulator from REG1 to REG8,
except REG7
TSDF
bit
False
0
True
1
Regulator Fault Register
The 34704 assigns a 1-bit register for each regulator
(FAULTx Register) to indicate that a fault had occurred on
each regulator. The processor can just access this register
periodically to determine system status. This reduces the
access cycles. If a regulator fault register asserted, then the
processor can access that regulator’s registers to see what
kind of fault had occurred.
FAULT
bit
False
0
True
1
SPECIAL REGISTERS
REG3 Fine Voltage Scaling Register
Regulator 3 has an additional fine output voltage scaling
that enables to lower the output voltage in 0.5% steps. The
34704 assigns an 8-bit register (REG3DAC) to the REG3
Digital to analog converter for the FB3 voltage generation.
Output votlage must be reduced gradually to avoid a OV/UV
fault to occur.
REG7 Independent ON/OFF Control (Only on 34704A)
The 34704B provide two register to independently turn on
REG7 when REG6 is not needed. Care must be taken when
turning on REG7 to avoid inrush currents during regulator
ramp-up. Following Process must be followed to assure
successful turn on of REG7.
1. Set EN0 and clear DISCHR_B on REG7CR0 register
2. After 1ms or more, set EN1 on REG7CR0 register
3. Set REG7DAC register to $00
4. Gradually shift up REG7DAC register from $00 to $D9
to ramp-up the output voltage in a soft-start like wave.
Soft start timing is dependant of I2C communication
speed and number of bit you change per writing, for
instance use 4,8 or 16 bits increase to ramp up the
output voltage.
Register Address
1
$58
2
$58
3
$59
4
$59
5
$59
6
$59
...
...
Code
$50
$D0
$00
$04
$08
$0C
...
55
$59
$D9
REG7 independent start up example
Analog Integrated Circuit Device Data
Freescale Semiconductor
34704
33