ACT81460
Rev 1.0, 18-Dec-2018
Where VSET is the decimal equivalent of the value in
the I2C VSET register. The VSET register contains an
unsigned 6-bit binary value. As an example, if VSET
register contains 011100 (28 decimal), the output volt-
age is 12.00V.
Boost Sink Current (mA)
ISET [5:3]
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
Table 7 shows the output voltage in voltage as a func-
tion of the VSET register setting.
0.00
0.63
1.25
1.88
2.50
3.13
3.75
4.38
5.00
5.63
6.25
6.88
7.50
8.13
8.75
9.38
10.00
10.63
11.25
11.88
12.50
13.13
13.75
14.38
15.00
15.63
16.25
16.88
17.50
18.13
18.75
19.38
20.00
20.63
21.25
21.88
22.50
23.13
23.75
24.38
25.00
25.63
26.25
26.88
27.50
28.13
28.75
29.38
30.00
30.63
31.25
31.88
32.50
33.13
33.75
34.38
35.00
35.63
36.25
36.88
37.50
38.13
38.75
39.38
Boost Output Voltage (V)
VSET [5:3]
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
5.00
5.25
5.50
5.75
6.00
6.25
6.50
6.75
7.00
7.25
7.50
7.75
8.00
8.25
8.50
8.75
9.00
9.25
11.00
11.25
11.50
11.75
12.00
12.25
12.50
12.75
13.00
13.25
13.50
13.75
14.00
14.25
14.50
14.75
15.00
15.25
15.50
15.75
16.00
16.25
16.50
16.75
17.00
17.25
17.50
17.75
18.00
18.25
18.50
18.75
19.00
19.25
19.50
19.75
20.00
20.25
20.50
20.75
Table 8. Boost Sink Current vs ISET Register
9.50
9.75
Dynamic Voltage Scaling
10.00
10.25
10.50
10.75
The boost does not have dynamic voltage scaling.
Enable / Disable Control
During normal operation, boost voltage and current sink
can be independently enabled or disabled via the I2C
interface. The voltage enable is controlled by the
boost’s ON bit. Note that disabling a the boost if it is
used as an input trigger to another regulator may or may
not disable the other regulators following it, depending
on the specific CMI settings. The constant current can
be disenabled by writing a value of 0mA to the ISET bits.
It is enabled by writing a non-zero value.
Table 7. Vout vs VSET Register Setting
Active Semi recommends that the boost converter’s out-
put 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. Note that making large
voltage steps will result in an UV/OV fault. If a large volt-
age change is required, change the voltage in multiple
small steps. To prevent an UV/OV fault caused by
changing the voltage when the boost is enabled, do not
increase VSET in steps larger than 30% or decrease
VSET in steps larger than 10% of the previous setting.
Keeping the voltage steps smaller than these levels
POK and Output Fault Interrupt
The boost converter contains an internal Power-OK
(POK) signal that can be used to sequence other power
supplies. This status is not available to the I2C interface.
POK threshold is typically 30% below the programmed
regulation voltage.
The boost converter does have I2C register undervolt-
age and overvoltage fault bits. These bits can be
masked. When masked, they provide real-time fault sta-
tus. If the nFLTMSK bits are set to 1, the ACT81460 in-
terrupts the processor if the boost output voltage goes
above or below the fault thresholds. In this case, nIRQ
asserts low and remains asserted until either the regu-
lator is turned off or goes back into regulation and the
fault bit has been read via I2C. The fault bit is cleared
when the register is read and the fault is no longer pre-
sent.
Output Current Setting
The boost converter regulates to the sink current de-
fined by I2C register ISET. It can be programmed be-
tween 0mA and 39.375mA in 0.625mA steps. The fol-
lowing equation calculates the sink current based on the
ISET register setting.
Isink = ISET * 0.625mA
Where ISET is the decimal equivalent of the value in the
I2C ISET register. The ISET register contains an un-
signed 6-bit binary value. As an example, if ISET regis-
ter contains 101000 (40 decimal), the sink current is
25mA.
Overcurrent and Short Circuit Protection
The boost converter features a cycle-by-cycle current
limit on the low side MOSFET. As with any standard
Table 8 shows the sink current as a function of the ISET
register setting.
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