BQ2002T: BQ2002T: Understanding the eval kit schematic

HPB

Part Number: BQ2002T
Other Parts Discussed in Thread: LM317, , BQ2002

I've been looking at the eval kit schematic for the BQ2002T charger and I do not understand how the CC pin controls the LM317 and how it affects the charge control. The sections of the schematic are highlighted in red boxes. Can anyone please explain? The document does not go into much detail about how this works. I'm trying to design this for a 2 NiMH cells.

over 6 years ago

0 HPB over 6 years ago

Expert 1350 points

EDIT: I think I understand the top left part of the schematic. It essentially enables the supply of Vcc to the BQ2002 only when a battery is present. Is that correct?

0 Bill Johns over 6 years ago in reply to HPB

TI__Guru 70006 points

Hello
1.) Top Left -- VCC Regulator Circuit, R1, D1 and C1 form a 5V regulator creating VCC voltage. Q1 will act as a switch to turn off VCC if input voltage is lower than battery voltage.
2.) Lower Right -- Current Regulator -- U2 / LM317T is configured as a current regulator. R7 is sized so that it will develop 1.2V between Vout and ADJ. Q2 is used to turn off the current regulator, it is under the control of CC pin on bq2002.

0 HPB over 6 years ago in reply to Bill Johns

Expert 1350 points

Thank you!

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BQ2002T: BQ2002T: Understanding the eval kit schematic