LTC1759
Production
The LTC1759 Smart Battery Charger is a single chip charging solution that dramatically simplifies construction of an SBS compliant system. The LTC1759...
Datasheet
LTC1759 on Analog.com
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)
Hi Victor2021,
Your schematic shows Q303 is inserted backwards. This will allow the battery to put a voltage on DCIN and the UV pin when it should not have it. This might contribute to the problem but not 100% certain. It would be best to install Q303 with the source on the VCC side so it can operate correctly.
Hello, ron.p
Thank you for your kind reply.
I just understand that Q303 out a reverse connection.
Oops, it seems I overlooked it. I try modify the prototype board and see what happens.
When I checked the prototype board carefully, Q303 was not reverse connected. The circuit diagram is wrong.
I am concerned about the short circuit failure of D319 (SBD).
(Although it is desirable that there is no inrush current.)
Please advise me.
When I checked the prototype board carefully, Q303 was not reverse connected. The circuit diagram is wrong.
I am concerned about the short circuit failure of D319 (SBD).
(Although it is desirable that there is no inrush current.)
Please advise me.