Post Go back to editing

LTC1759: IC fails due to overvoltage when connecting battery.

Category: Hardware
Product Number: LTC1759

Hello,

I used the LTC1759 to design a smart battery charger. The other party's pack manager IC is bq40z50-R3.

The voltage of the battery pack is typ.11.1V.

The circuit I designed is a slight modification of TYPICAL APPLICATION. I will post the circuit diagram.

If the battery is connected when DCIN and VDD are not supplied, the low-side MOSFET will turn on momentarily after a short time has passed after the battery was connected.

The SW terminal waveform at that time is CH2 with waveform 1, and is boosted to a maximum of 13.8V.

CH4 is the battery current. (Use a current probe. Negative value is discharge)

Waveform 2 is the waveform when the battery is then removed and reconnected within 30 seconds.

The SW terminal voltage rises from 0V and rises up to 20.4V. In my opinion, this is because the low-side MOSFET is on and turns off after the battery is connected, so the L301 is functioning as a boost coil.

It was okay when I got this waveform, but there were multiple short circuit failures on the LTC1759 and D319(SBD).

 

Question.

Why does the charging IC bother to generate an inrush current?

Is this normal operation?

Is there a solution to prevent inrush current?

Sincerely yours,

--

Q301, Q302: RS1G120MNTB (40V, 34A NchMOSFET, ROHM)

Q303: TJ40S04M3L (-40V, -40A PchMOSFET, Toshiba)

D319: D1FH3 (30V, 3A SBD, ShinDengen)

L301: CDRH127/LDNP-220MC (22uH, 4.7A Inductor, Sumida)

(最小値 = minimum value)

(最大値 = Maximum value)