ACT4921 datasheet(16/35 Pages) QORVO

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

16 of 35

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ACT4921

Power Loss Protection with 6A eFuse

SUPPLEMENT State

The IC enters SUPPLEMENT state when it detects a

fault condition. It opens the eFuse to bi-directionally

disconnect the input from the output. It automatically

turn on the buck converter to power the output from the

storage capacitors. The following five conditions move

the IC into SUPPLEMENT state.

VINS voltage below UV threshold

VINS voltage above the OV threshold

Input voltage above the OV threshold

eFuse current above the OC threshold

VIN – VOUT > 300mV

SUPPLEMENT-DISABLE State

In the SUPPLEMENT-DISABLE state, VOUT is good

and can power the system, but the IC cannot transition

to the SUPPLEMENT state. While in this state, the open

drain output PG_STR status at LOW.

In typical startup sequence, when the ACT4921 exits

the SOFTSTART state, it transitions though the

NORMAL state directly to SUPPLEMENT-DISABLE

state. While IC is in SUPPLEMENT-DISABLE state, the

blocking FET gets turned on by the ENB pin or the

EN_BFET bit in register 0x06h. The blocking FET

sources 300mA constant current to charge the storage

caps to VIN. Then the boost converter turns on to

charge the storage caps to their final voltage. When the

storage capacitor is fully charged, the ACT4921 exits

SUPPLEMENT-DISABLE state and moves to NORMAL

state. The transition of PG_STR pin from low to high

indicates that the IC transitioned to the NORMAL state.

The ACT4921 checks the following conditions to make

sure the operating conditions and external components

are within speck and working properly so the IC is

capable of entering SUPPLEMENT state to provide

backup power. If the IC Is operating in the NORMAL

state and one of the following becomes invalid, the IC

notifies the system by pulling nIRQ low and then enters

the SUPPLEMENT-DISABLE state.

VOUT-VB < 200mV

Die temperature <145°C

LDO (REF) is valid

Bootstrap capacitor at HSB pin properly

connected

The buck compensation is present and not

shorted.

SHUTDOWN State

SHUTDOWN disables all IC functionality to protect

against extreme over temperature conditions above

155°C. This includes shutting off the eFuse. I2C

functionality not available in this state. The IC transitions

to SOFT-START when the junction temperature drops

and there is no overcurrent fault.

The following figures and tables help describe the

ACT4921 states and functionality in different situations.

Figure 3 shows the ACT4921 State Diagram. Table 1

shows which functions are enabled in each state. Table

2 shows how different operating conditions and faults

affect different IC functionality. Note that the current

operating state can be determined by reading the I2C

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