MCS1632R005FER datasheet(21/46 Pages) ONSEMI

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FAN54161

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VFAIL Detection

In bypass charging applications, a failure of the bypass

charging switch (however, this is rare) could result in the

travel adapter output being directly connected to the battery

pack which can cause a potentially dangerous system

fault. A VFAIL comparator monitors the voltage at PMID

while the bypass switch is open to detect the presence of a

leakage path from VBUS to PMID (when TA is attached) or

VOUT to PMID (when battery is connected) which would

indicate a failure in the bypass charging FET. During VFAIL

detection, a RFAIL pulldown resistor is connected to PMID

and a comparator checks if the PMID voltage exceeds the

VFAIL threshold. RFAIL will be disconnected from PMID

anytime the bypass switch is enabled to avoid power

consumption during bypass charging.

If the detection determines that VPMID > VFAIL for more

than tVFAIL_GLTCH, the FAN54161 will:

1. Set the VFAIL_INT bit to 1 and pull the INT_N

pin low

A VFAIL interrupt alerts the host that damage to the bypass

charging FET has occurred. The host can then alert the

system bypass charging controller to clamp the travel

adapter’s output voltage to the battery pack’s float voltage

to prevent an overcharge of the battery. Additionally, the

host can alert the end user that the portable device is

damaged and should be returned for repair.

If VFAIL_EN=1, VFAIL detection is momentarily

activated when:

1. SW_EN is set from 0 to 1, while ADC_EN=0 and

RESET_N=1. VFAIL detection occurs before the

charge pump gate drive turns on the bypass

charging FET but after the main bandgap reference

is enabled

2. ADC_EN is set from 0 to 1, while SW_EN=0 and

RESET_N=1

Regulation Loops

Figure 11 illustrates the logic that causes the FAN54161

to enter regulation mode.

Either of the following four fault protections being

triggered can cause the switch to operate in regulation mode

as follows:

1. If the voltage at VOUT exceeds VOREG(TH), and

VOREG_EN=1, the bypass switch will be

regulated such that VOUT is limited to VOREG(TH).

2. If the voltage across SNSP and SNSN exceeds

VBATREG(TH), and VBATREG_EN=1, the bypass

switch will be regulated such VBAT is limited to

VBATREG(TH).

3. If IBAT (sensed as a voltage across SRP and SRN)

exceeds IBATREG(TH), and IBATREG_EN=1, the

bypass switch will be regulated such that IBAT is

limited to IBATREG(TH).

4. If IBUS (from VBUS to VOUT) exceeds

IBUSREG(TH), and IBUSREG_EN=1, the bypass

switch will be regulated such that IBUS is limited

to IBUSREG(TH).

It must be noted that the switch essentially becomes more

resistive during regulation mode. This will cause more

power dissipation in the switch and a greater likelihood of

the junction temperature reaching or exceeding the

shutdown threshold TSDN(TH). Therefore it is imperative for

the system host controller to update the system

configuration such that none of the above four monitors are

triggered. This can be done by increasing the thresholds in

the FAN54161 or changing other external system

parameters (ex: adapter voltage or current limit).

MCS1632R005FER Datasheet(PDF) 21 Page - ON Semiconductor

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