ACT4921 datasheet(15/35 Pages) QORVO

15 / 35 page

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

15 of 35

www.qorvo.com

ACT4921

Power Loss Protection with 6A eFuse

Basic Non-Volatile – These are R/W and RO. After the

IC is powered, the user can modify the R/W register

values

change

functionality.

Changes

functionality include things like output voltage settings,

startup delay time, and current limit thresholds. Any

changes to these registers are lost when power is

recycled. The default values can be modified at the

factory

optimize

functionality

for

specific

applications. Please consult Qorvo for custom options

and minimum order quantities.

When modifying only certain bits within a register, take

care

not

inadvertently

change

other

bits.

Inadvertently changing register contents can lead to

unexpected device behavior.

State Machine

ACT4921 contains an internal state machine with seven

internal states: UV/POR, SOFT-START, NORMAL,

HEALTH CHECK, SUPPLEMENT, SUPPLEMENT-

DISABLE, and SHUTDOWN.

UV/POR State

The IC enters the UV/POR state on power up. It also

enters UV/POR from SUPPLEMENT state in the

following conditions:

When the input voltage drops below the

VINS_UV threshold.

When the storage capacitor voltage drops

below 3.0V.

When the buck converter output voltage goes

OV or UV.

The user may force the IC into UV/POR by writing a 1

into the FORCE_PWROFF bit, register 0x06h, bit 0.

When entering UV/POR from power up, all registers

reset to their default state. The registers retain their

existing values when the IC enters from SUPPLEMENT

state or from SHUTDOWN EFUSE. The IC transitions

from the UV/POR state to the SOFT-START state when

EN pin is high, the input voltage is above UVLO, the

VINS pin is above 0.64V, and the startup delay softstart

timer has timed out. The delay timer is set by I2C

shows the allowable delay times. 1ms is typically an

acceptable delay time, but longer times can be

programmed if the input voltage source rises extremely

slowly.

Table 1: Softstart Delay

EN_STARTDLY[3:1]

Startup Delay Time

000

Not valid

001

1ms

010

5ms

011

10ms

100

20ms

101

40ms

110

80ms

111

125ms

SOFTSTART State

In the SOFTSTART state, the IC slowly turns on the

eFuse to minimize inrush currents. The SS pin directly

controls the maximum output voltage dV/dt. The IC

stays in the SOFTSTART state until VIN-VOUT <

200mV and a 1ms timer times out. PG_VO goes high

when the IC exits the SOFTSTART state.

NORMAL State

The NORMAL state is the normal operating state. The

eFuse is fully on, VOUT = VIN, and the IC provides full

operating current. When the IC transitions from the

SOFTSTART state to the NORMAL state, the PG_VO

pin immediately goes high and the IC starts charging the

storage capacitors if ENB is pulled high.

HEALTH CHECK State

The HEALTH CHECK state can be considered a sub-

state of the NORMAL state. The IC operates identical to

the NORMAL state with the addition of activating the

circuitry that check the storage capacitor health. The IC

automatically enters HEALTH STATE every four

minutes. The user may also manually enter this state by

writing a 1 into the FORCE_HLTHCHK bit which is bit 1

in register 0x06h. This bit automatically resets to 0 after

the

health

check

routine

completes.

The

automatically exits HEALTH CHECK and enters

SUPPLEMENT state in a fault condition.

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