ACT4921 datasheet(27/35 Pages) QORVO

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

27 of 35

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ACT4921

Power Loss Protection with 6A eFuse

use of super capacitors, electrolytic, polymer, Tantalum,

ceramic, or any capacitors in the design.

Output Voltage UVLO Setting

The storage capacitor power good signal indicates that

the STR voltage is above the UVLO threshold. The

UVLO threshold is shared with the storage capacitor

health check, and is set by the I2C register HMON_THR

[3:0]. The default value is determined by the IC’s

specific CMI option.

Table 8: Storage Capacitor PG Threshold

HMON_THR[2:0]

HMON_THR[3]

000

95.0%

96.6%

001

95.2%

96.8%

010

95.4%

97.0%

011

95.6%

97.2%

100

95.8%

97.4%

101

96.0%

97.6%

110

96.2%

97.8%

111

96.4%

98.0%

STORAGE CAPACITOR HEALTH

MONITOR

General Description

The ACT4921 has an internal health monitor for the

storage capacitors. It applies a constant current sink to

the capacitors and monitors the voltage drop. If the

voltage drops below a predetermined threshold, the IC

asserts nIRQ to indicate that the storage capacitance

has dropped below the allowable threshold. Health

monitoring is completely autonomous, but can also be

manually initiated by the system uP. Health monitoring

can also be configured so that it is only a manual

operation so it can be triggered on demand to avoid any

critical

system

operations.

The

health

monitor

parameters are adjustable via I2C registers to allow

flexibility for different capacitor values.

Health Monitor Algorithm

The health check algorithm sinks 10mA into the STR pin

for a time determined by I2C register HMON_TSET. It

then sinks 50mA for 200us. It monitors the voltage on

the STR pin, and if the voltage drops more than the

percentage set by I2C register HMON_THR, it asserts

nIRQ low and sets the fault bit. The IC’s specific CMI

option sets the default HMON_TSET and HMON_THR

settings. After the HMON_TSET time, the boost turns

back on to recharge the storage capacitor.

The health check function can be enabled and disabled

by the DIS_HEALTH_CHK bit 0x0Bh [4]. It also can be

forced to perform a one-shot health check by the

FORCE_HLTHCHK bit 0x06h [1]. Forcing a single

health check is valid even when the DIS_HEALTH_CHK

bit = 1. If set in continuous mode, the IC performs a

health check every 4 minutes. This timing can be

configured for every 8 minutes or 16 minutes by bits

SCALE_HCHK _2X and SCALE_HCHK _4X in register

0x10h [1:0].

The ACT4921 allows for very flexible health checking

routines by allowing the system to manually enable the

10mA

discharge

current

setting

the

EN_STR10mASINK bit 0x06h [2] = 1. In this situation,

the system manually turns the discharge current on and

off. The storage capacitor voltage threshold is still

determined by the HMON_THR register. This function is

useful for checking extremely large capacitor values

which need very long discharge times.

PG_THR

(Programmable)

VSTR

Initial Charge

Health Testing

Top-Off

Maintain

10mA

50mA

200us

Programmable

Discharge Time

Pr ogrammable

Interval Time

St orage Cap Voltag e

Discharge Current

Figure 6: Storage Voltage at Different Stages

The register HMON_TSET [3:0] sets the health check

discharge time as shown in Table 9.

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