ACT88430QJ-T
Rev 1.0, 24-Oct-2018
if needed. Each converter contains an optional inte-
grated discharge resistor that actively discharges the
output capacitor when the regulator is disabled. Each
LDO’s discharge function is enabled via its I2C bit
DIS_PULLDOWN.
LDO3
0x81h
RANGE_LDO3
0
Output-High
The programming range for Output-Low is 0.8V to
2.375V in 25mV steps.
Soft-Start
VLDOx = 0.8V * LDOxVSET * 0.025V
Each LDO contains a softstart circuit that limits the rate
of change of the output voltage, minimizing input inrush
current and ensuring that the outputs power up in a
monotonically. This circuitry is effective any time the
LDO is enabled, as well as after responding to a short
circuit or other fault condition. Each LDO’s softstart time
is adjustable via its I2C bits SS_RAMP.
Where LDOxVSET is the decimal equivalent of the
value in each regulator’s I2C LDOxVSET register. The
LDOxVSET registers contain an unsigned 6-bit binary
value. As an example, if LDO 1’s LDOxVSET register
contains 101000b (40 decimal), the output voltage is
1.8V.
The programming range for Output-High is 2.0V to
3.575V in 25mV steps.
LDO1 is adjustable between 226µs and 570µs, depend-
ing on output voltage.
V
LDOx = 2.0V * LDOxVSET * 0.025V
LDO2 is adjustable between 130µs and 220µs, depend-
ing on output voltage
Where LDOxVSET is the decimal equivalent of the
value in each regulator’s I2C LDOxVSET register. The
LDOxVSET registers contain an unsigned 6-bit binary
value. As an example, if LDO 1’s LDOxVSET register
contains 01010000b (52 decimal), the output voltage is
3.3V.
LDO3 is adjustable between 65µs and 130µs, depend-
ing on output voltage
Table 5 summarizes the LDO softstart programming
ranges.
Active Semi recommends that an LDO’s output voltage
be kept within +/- 25% of the default output voltage to
maintain accuracy. Voltage changes larger than +/- 25%
may require different factory trim settings (new CMI) to
maintain accuracy.
Table 5: LDO Softstart Ranges
LDOx
Softstart
Register
LDO1
softstart
(us)
LDO2
softstart
(us)
LDO3
softstart
(us)
Setting
00
01
10
11
226
323
440
570
130
133
170
220
36
64
LDOx_SS
96
Overcurrent and Short Circuit Protection
126
Each LDO provides overcurrent and short circuit protec-
tion. The overcurrent threshold is set by the LDOx_ILIM
I2C bits. In both an overload and a short circuit condition,
the LDO limits the output current which causes the out-
put voltage to drop. This can result in an undervoltage
fault in addition to the current limit fault. If an LDO
reaches current limit protection, the status is reported in
the ILIM_REG[x] I2C registers. The contents of these
registers are latched until read via I2C. When the cur-
rent limiting results in a drop in output voltage that trig-
gers an undervoltage condition, the IC shuts down all
power supplies, asserts IRQ low, and enters the
UVLOFLT state. The IC restarts in 100ms and starts up
with default sequencing. Overcurrent and short circuit
conditions can be masked via the I2C bit
LDOx_ILIM_FLTMSK.
Output Voltage Setting
LDO1/2/3 regulate to the voltage defined by I2C regis-
ters LDO VSET registers. Unlike the buck converters,
the LDOs only have one VSET register. LDO2/3 each
have two programmable output voltage ranges, Output-
Low Range and Output-High Range. Each LDO’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 rec-
ommend changing the output voltage range from its de-
fault setting because its internal voltage reference is
only trimmed to its default setting. The following table
shows which I2C bits set the output ranges.
Table 6: LDO Output Voltage Programming Ranges
Input Capacitor Selection
Register
Bit
Setting
Range
Each LDO requires a high quality, low-ESR, ceramic in-
put capacitor. A 1uF is typically suitable, but this value
can be increased without limit. The input capacitor is
should be a X5R, X7R, or similar dielectric.
LDO1
LDO2
n/a
n/a
RANGE_LDO2
n/a
Output-High
1
0
1
Output-Low
Output-High
Output-Low
0x81h
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ActiveSwitcherTM is a trademark of Active-Semi.
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35
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