ACT4910QW
Rev 1.0, 15-Sept-2017
Where Vripple is the desired output ripple voltage, FSW is
the switching frequency in Hz, and ΔIL is the maximum
ripple current in Amperes.
Operating Mode
The boost converter operates in peak current mode,
non-fixed frequency mode. The power FET stays on
until its current reaches programmed peak current. It
then turns off until the inductor current drops to 0A, at
which time it turns on again.
As with the input capacitor selection, use X5R or X7R
dielectrics and be sure to consider the capacitor’s DC
bias effects.
Storage Capacitor Voltage Setting
Storage Boost Converter
The buck converter output voltage is set by either the
I2C register BSTVSET[4:0], or a combination the
register and a resistor placed between the BSET pin to
VSS.
General Description
The ACT4910 contains an integrated peak current-
mode, synchronous boost converter. It minimizes
system level costs by using the same components as
the buck converter. The peak current is adjustable
between 250mA and 950mA, allowing for system
optimization. The output voltage is adjustable between
5V and 36V via I2C registers and an external resistor.
The peak current-mode control topology eliminates the
need for compensation. The boost automatically
charges up the storage capacitors from the input
voltage so they are ready to provide backup power in
the event of a system fault.
When using only the BSTVSET[4:0] leave the BSET pin
floating. Table 5 shows the programmed storage voltage.
The default value is determined by the IC’s specific CMI
option.
Table5: Storage Capacitor Voltage Settings with
BSET Pin Open
BSTVSET[4]
BSTVSET[3:0]
0
1
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
5V
5.6V
7V
8V
9V
10V
11V
12V
13V
14V
15V
16V
17V
18V
19V
20V
21V
22V
23V
24V
25V
26V
27V
28V
29V
30V
31V
32V
33V
34V
35V
36V
Startup
The boost converter automatically starts when the IC
exits the SOFTSTART state. Note that the IC exits the
SOFTSTART state 10ms after the output voltage is
within 200mV of the input voltage.
When the storage voltage reaches regulation, the boost
enters standby mode and monitors the storage voltage.
It automatically turns back on and “tops off” the storage
capacitors when the storage voltage drops below 95%
of the programmed voltage. The boost converter
automatically turns off if it is “topping off” the storage
capacitors when the IC enters supplement mode.
The average input current when the boost charges the
storage capacitors is approximately ½ of the peak
switching current. The peak switch current is programed
by register BST_CLIM[1:0].
Using both the BSTVSET[4:0] register and an external
resistor provides additional output voltage resolution. In
this configuration, the following equation calculates the
output voltage.
Table 4: Boost Peak Current Settings
BST_CLIM[1:0]
(mA)
250
00
01
10
11
650
ꢁ
꣎ꢝ꣏ꢢ
ꢓꢜꢁ
ꢘ ꢓꢜꢟꢓꢜ
∗
ꢀꢀꢀꢀ
Equation 8
950
꣐ꢚ꣑Ω
1500
Where VBSTVSET is the voltage set by the BSTVSET
register in Table 5 and RBSET is the resistor on the BSET
pin in ohms.
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Copyright © 2017 Active-Semi, Inc.
23
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