ACT4921 datasheet(26/35 Pages) QORVO

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Data Sheet Rev. B, January 2020 | Subject to change without notice

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ACT4921

Power Loss Protection with 6A eFuse

Table 6: Boost Peak Current Settings

BST_CLIM[1:0]

(mA)

250

500

950

1500

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.

Storage Capacitor Voltage Setting

The buck converter output voltage is set by either the

I2C register BSTVSET[4:0], or a combination the

VSS.

When using only the BSTVSET[4:0] leave the BSET pin

floating. Table 6 shows the programmed storage voltage.

The default value is determined by the IC’s specific CMI

option. Note that the IC accepts BSTVSET values

between 11000 and 11111 and each of these values

sets the boost voltage to 28V.

Table 7: Storage Capacitor Voltage Settings with

BSET Pin Open

BSTVSET[3:0]

BSTVSET[4]

0000

21V

0001

5.6V

22V

0010

23V

0011

24V

0100

25V

0101

10V

26V

0110

11V

27V

0111

12V

28V

1000

13V

28V

1001

14V

28V

1010

15V

28V

1011

16V

28V

1100

17V

28V

1101

18V

28V

1110

19V

28V

1111

20V

28V

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.

7 8

' 8

60 9:

(9)

Where VBSTVSET is the voltage set by the BSTVSET

pin in ohms.

As an example, to set the storage voltage to 12.8V

when the default BSTVSET[4:0] = 10111, first look up

the storage voltage when the BSET pin is open per table

7. This sets VBSTVSET = 28V. Using equation 8, setting

RBSET = 27.4kΩ sets VSTR = 12.8V. Note that RBSET

should be set between 20kΩ and 60kΩ. Setting RBSET

below 20kΩ gives the same result as using a 20kΩ

resistor. Setting RBSET above 60kΩ gives the same

result as using a 60kΩ resistor. Using RBSET outside the

range is acceptable and does not damage the IC.

Input Capacitor Selection

There are no special considerations for the boost

converter input capacitor. The IC topology uses the

buck converter output capacitor for the boost input

capacitor. Proper selection of the buck converter output

capacitor automatically results in an acceptable boost

converter input capacitor.

Output Inductor Selection

There are no special considerations for the boost

converter inductor. The IC topology uses the buck

converter inductor for the boost converter inductor.

Proper selection of the buck converter output capacitor

automatically results in an acceptable boost converter

input capacitor.

Output Capacitor Selection

The IC topology uses the buck converter input capacitor

for the boost converter output capacitor. Note that the

storage capacitors are also included in the boost

converter output capacitors. Proper selection of the

buck converter input capacitor typically results in an

acceptable boost converter output capacitor. The boost

output capacitor has two criteria. The first is that it must

consist of at least 10µF of high quality X5R or X7R

ceramic capacitance placed directly between the STR

pin and PGND. The second criteria is that the sum of

the ceramic capacitor and storage capacitors must be

greater than 100µF. There is no requirement for the

additional capacitance dielectric material. This provides

flexibility for the storage capacitors, which allows the

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