BQ24773 - discrepancies between the datasheet and the EVM User's Guide

Massimiliano De Cristofaro

Expert 6640 points

Other Parts Discussed in Thread: BQ24773

Dear team,

a customer of mine has the following questions about the BQ24773:

The 1uF capacitor on VCC: The datasheet connects it to "signal ground", but the EVM connects it to "power ground"
The BAT pin in the EVM shows it is an output pin, but the datasheet states it is an input.
The placement of the 100nF "filter" cap on BAT input: The datasheet says it should be as close to pin 17 as possible (makes sense), but in the schematics (in the datasheet AND EVM) shows that it is on the other side of the 10 ohm series resistor (does not make sense).
The datasheet mentions that the output capacitor should be AFTER the sense resistor (on the SRN) side, but the schematics (in the datasheet AND EVM) shows capacitors between the inductor and sense resistor. I suspect the latter is better, because one is not really interested in the inductor current, but in the smoothed out current going to (or coming from) the battery.

Could you please advice?

Thanks a lot in advance for your help.

Best regards,

Massimiliano De Cristofaro

Application Support Engineer - Power Management

ASKTEXAS DiamondLane – EMEA Distribution Support

Texas Instruments Deutschland

over 9 years ago

0 Massimiliano De Cristofaro over 9 years ago

TI__Expert 6640 points

Dear team,

any news?

Thanks a lot.

Best regards,
Massimiliano

0 Massimiliano De Cristofaro over 9 years ago in reply to Massimiliano De Cristofaro

TI__Expert 6640 points

Dear team,

the customer asked also this other question:

5. How critical is a very low gate charge for the BATFET in the BQ24773 design (Q3 in EVM circuit)? To use a dual P-channel MOSFET (like SI7997DP) for the BATFET in a common source configuration, be able to disconnect the battery to switch off the BQ24733. The circuit should only switch on again when "AC input" is restored.

Could you please advice?

Thanks a lot.

Best regards,
Massimiliano.

0 Wang5577 over 9 years ago

TI__Guru 56650 points

Datasheet should have most important and correct info.
1. VCC powers ic internal LOD. It should be on small signal ground. If VCC ground is very close to IC ground and no high current flows on it, it should be OK on power ground.
2. BAT is input pin.
3. 0.1uF BAT capacitor should not give extra delay because it is feedback pin. So, put it on the other side of the 10ohm.
4. bq24773 is a NVDC charger. The system load is on SRP side. So, we put capacitors on SRP side to help customer evaluate their system.

0 Wang5577 over 9 years ago in reply to Wang5577

TI__Guru 56650 points

I don't think bq24773 can support a back to back FET because it supports supplement mode if the system load power is higher than input current limit. If we use a back to back FET, it can't be immediately turned on. The system may loss the power.

0 Massimiliano De Cristofaro over 9 years ago in reply to Wang5577

TI__Expert 6640 points

Dear Wang,

thanks a lot for your support!!

Best regards,
Massimiliano.

0 Mihir Bhatt over 8 years ago in reply to Wang5577

Intellectual 290 points

What a bout the voltage drop across the BATFET in case there is no power adapter and the system load is around 10A.

Will the BATFET will conduct and the drop will remain as per RDS(on)?

0 Wang5577 over 8 years ago in reply to Mihir Bhatt

TI__Guru 56650 points

Yes. The BATFET will conduct and the drop will remain as per RDS(on).

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BQ24773 - discrepancies between the datasheet and the EVM User's Guide