ACT88430QJ-T
Rev 1.0, 24-Oct-2018
changing the output voltage range from its default set-
ting because its internal voltage reference is only
trimmed to its default setting. The following table shows
which I2C bits set the output ranges.
Enable / Disable Control
When power is applied to the IC, all converters automat-
ically turn on according to a pre-programmed sequence.
Once in normal operation (ACTIVE state), each con-
verter can be independently disabled via I2C. Each CMI
version requires a different set of command to disable a
converter, so contact the factory for specific instructions
if needed. Each converter contains an optional inte-
grated discharge resistor that actively discharges the
output capacitor when the regulator is disabled. The dis-
charge function is enabled via the I2C bit Bx_DisPull-
down.
Table 4: Buck Output Voltage Programming
Ranges
Register
0x74h
0x72h
0x89h
n/a
Bit
Setting
Range
0
1
0
1
0
1
Output-Low
Output-High
Output-Low
Output-High
Output-Low
Output-High
Buck1
Buck2
Buck3
Buck4
SEL_REF0P8_BUCK1
SEL_REF0P8_BUCK2
SEL_REF0P8_BUCK3
n/a
Soft-Start
n/a
Output-High
Each buck regulator contains a softstart circuit that lim-
its the rate of change of the output voltage, minimizing
input inrush current and ensuring that the outputs power
up monotonically. This circuitry is effective any time the
regulator is enabled, as well as after responding to a
short circuit or other fault condition. Buck1/2/3 softstart
time is adjustable between 150µs to 485µs via their I2C
SS_RAMP registers. Buck4 softstart time is adjustable
between 25µs to 204µs via I2C SS_RAMP register. Ta-
ble 3 summarizes the softstart settings. Table
The programming range for Output-Low is 0.6V to
3.000V in 9.375mV steps.
V
BUCKx = 0.6V * VOUTx * 0.009375V
Where VOUTx is the decimal equivalent of the value in
each regulator’s I2C VOUTx register. The VOUTx regis-
ters contain an unsigned 8-bit binary value. As an ex-
ample, if Buck 1’s VOUT0 register contains 10000000b
(128 decimal), the output voltage is 1.8V.
Table 3: Buck Softstart Time (0.8V Reference)
The programming range for Output-High is 0.8V to
3.988V in 12.5mV steps.
Buck1/2/3
Softstart (µs)
Buck4
Softstart (µs)
SS_RAMP
VBUCKx = 0.8V * VOUTx * 0.0125V
000
001
010
011
100
101
110
111
150
200
250
300
350
395
440
485
25
51
Where VOUTx is the decimal equivalent of the value in
each regulator’s I2C VOUTx register. The VOUTx regis-
ters contain an unsigned 8-bit binary value. As an ex-
ample, if Buck 1’s VOUT0 register contains 01010000b
(80 decimal), the output voltage is 1.8V.
76
102
127
153
178
204
Active Semi recommends that a buck converter’s output
voltage be kept within +/- 25% of the default output volt-
age to maintain accuracy. Voltage changes larger than
+/- 25% may require different factory trim settings (new
CMI) to maintain accuracy.
Note that when an output’s reference voltage is
changed to 0.6V, the softstart time changes to 75% of
the time in Table 3.
100% Duty Cycle Operation
The buck regulators are capable of operating at up to
100% duty cycle. During 100% duty cycle operation, the
high-side power MOSFETs are held on continuously,
providing a direct connection from the input to the output
(through the inductor), ensuring the lowest possible
dropout voltage in battery powered applications.
Output Voltage Setting
Buck1/2/3/4 regulate to the voltage defined by I2C reg-
ister VSET0 in normal operation and by VSET1 in DVS
mode. Buck1/2/3/4 each have two programmable out-
put voltage ranges, Output-Low Range and Output-
High Range. Each buck converter’s output range can be
programmed independently of the others. Note that the
output voltage range can NOT be changed while the
output is enabled. Active Semi does not recommend
Dynamic Voltage Scaling
Each buck converter supports Dynamic Voltage Scaling
(DVS). DVS allows the user to optimize the processor’s
energy to complete tasks by lowering the processor’s
operating frequency and input voltage when lower per-
formance is acceptable. In normal operation, each out-
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32
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