BQ77905: BQ77905 CHG Pin

john xiao

Part Number: BQ77905

Dear all:

I read BQ77905 datasheet page 27-29,if OV fault occurs and charger still present,Is there always a small current from the pack- to the CHG Pin?If so, is there any hidden danger?thanks a lot.

over 7 years ago

0 David Hien over 7 years ago

TI__Genius 10830 points

Hi John,
Your post has been assigned to one of our BMS experts.

Regards,
David

0 WM5295 over 7 years ago

TI__Guru 54715 points

Hi John,
If the pack is in OV with the CHG off, the CHG pin can be pulled below GND by the charger. There is no expected current. Figure 20 shows some current because the scope probe and input provide a 10M load between the charge FET gate and GND.

0 john xiao over 7 years ago in reply to WM5295

Intellectual 470 points

Hi WM:

in BQ77905 datasheet Figure 23,if the pack is in OV and charger still present,how the Q3 state?can you provide the CHG,CHGU,DSG Pin Internal circuit composition?thanks a lot.

0 WM5295 over 7 years ago in reply to john xiao

TI__Guru 54715 points

Hi John,
With OV CHG and CHGU are low. DSG is on. See 8.3.1 for OV description and table 3. CHGU is noted in 8.3.8.
When CHG is low, Q3 in figure 23 will be off since the gate-source voltage will be ~0. With the FET off the gate of Q1 can fall with PACK-. CHG actually has an internal FET which allows up to -30V. Figure 23 is intended when the voltage is more negative than -30V. For pin equivalent circuits see the application note www.ti.com/.../slua845

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BQ77905: BQ77905 CHG Pin