BQ2002: Need Reference Circuit for BQ2002 Using 5V USB Type-C for 3×AAA NiMH Charging

Hi Samidha

The BQ2002 is a very old family of devices that I would not recommend.

Have you looked at the BQ25172, NiMH charger see here.

Hi Bill,

Thanks for the quick response!

I’m specifically looking for an IC in SOIC or TSSOP package for ease of manual soldering.
Please suggest options that fit this.

Hi Samidha

Samidha Buriwar said:

Overcurrent protection, temperature cutoff (NTC), and USB-safe trickle/top-off modes.

Which BQ2002 variant (C, G, E, etc.) is best suited for this application?

The BQ2002T or 2002D are Temperature Cutoff devices, charge termination based on Delta T / Delta T.

This is what is used in the EVM design.

Hi Bill,

Thanks!

The EVM design recommends VDC = 4 V + VBAT, but in my case, VDC = 5 V (USB) and VBAT = 3.6 V (3×AAA NiMH).

What changes would be needed in the schematic to support this lower headroom?
Also, do you have any reference schematic using USB (5 V) with a BQ2002 IC?

Appreciate your guidance.

– Samidha

Hi Samidha

Do not have a 3S configuration reference design, checking on what needs to change.

Samidha Buriwar said:

I’m specifically looking for an IC in SOIC or TSSOP package for ease of manual soldering.
Please suggest options that fit this.

Is this a very limited prototype build that you will use manual soldering on?

Hi Samidha

What can you tell me about your applications and charge current?

The standard BQ2002 circuit is not a good fit for 5V input voltage charging 3S battery.

Hi Bill,

Thanks for the response.

This is for a handheld portable measuring instrument powered by 3×AAA NiMH cells.
The input is a standard 5 V USB Type-C, and I’m targeting a charge current of around 200–300 mA.

The design needs to be compact and simple, with support for temperature cutoff (NTC) and or basic overcurrent protection

I'm open to newer ICs if BQ2002 isn’t the best fit, but I prefer something in a SOIC or TSSOP package for ease of manual soldering

Would appreciate your suggestions!

– Samidha

Reviewing the schematics for further comment.

Juan Ospina

Hi Samidha

The best solution is the BQ25172, but hand soldering is not an option.  This is a 2mm X 2mm device with few external parts.  Designed to operate from a 5V USB input, has TS pin for temp cutoff and programable current regulation.  

The BQ2002 will use an LM317 as a current regulator but has a large Vin to Vout drop, LM317 is about 2V, current sense resistor is 1.25V, output diode is .7v.