BQ24079: Transition speed to supplement mode

Prithvi Raj Narendra1

Part Number: BQ24079
Other Parts Discussed in Thread: UCC28911, , TPS63802

Greetings,

We are looking to power a device with GSM modem which takes 2A peak current for 0.6 ms every 4.6 ms whenever it is communicating (2-3s). The two power sources that we are considering for this application are a buck DC-DC converter such as UCC28911 (70V Vin and 5V out with 0.5A max) and a Li-Ion battery (4.2-3.2V, 3.8V nominal). These two sources are to be selected automatically with DC-DC as higher priority. The output of the PPM is given to a buck-boost TPS63802 to give a stable 4V for GSM module. This is as shown in block diagram below where we feel BQ24079 is appropriate as the power path manager with its supplement mode, configuring the input limit as 0.5A.

Can BQ24079 go to supplement mode for a instantaneous spike of 2A for 0.6 ms? Do you see any other issue with this setup?

Thanks, Prithvi

over 3 years ago

0 Prithvi Raj Narendra1 over 3 years ago

Intellectual 550 points

Further questions assuming for all these questions CE* pin is high i.e. charging is disabled and input current limit is 500 mA:

1. If Vin is at 5V and system load is 50 mA, what is system output voltage? 5V?

2. When a 2A current is drawn by system load (GSM through TPS63802), what would the output voltage be? Battery voltage?

3. When this transition happens, if there is input cap at vout of BQ24079 at 5V, would there be reverse current flow into the IC which has moved to say battery voltage of 4V?

4. Same as previous question - time for the transition to supplement mode?

Thanks.

+1 Anthony P Pham over 3 years ago in reply to Prithvi Raj Narendra1

TI__Mastermind 23170 points

Hi Prithvi,

Prithvi Raj Narendra1 said:
If Vin is at 5V and system load is 50 mA, what is system output voltage? 5V?

The output voltage would be 5V as the VIN is not about the regulated output by the dropout voltage.

Prithvi Raj Narendra1 said:
When a 2A current is drawn by system load (GSM through TPS63802), what would the output voltage be? Battery voltage?

The device will enter supplement mode if the output voltage drops below VDPPM even though CE pin is high. If the battery and the input and battery can provide the system load the current in needs, it will be between VBSUP1 and VBSUP2.

Prithvi Raj Narendra1 said:
When this transition happens, if there is input cap at vout of BQ24079 at 5V, would there be reverse current flow into the IC which has moved to say battery voltage of 4V?

The device has reverse current protection, you can see this by powering the device in battery only and seeing no voltage on the IN pin. For supplement mode, the device will draw power from the battery.

Prithvi Raj Narendra1 said:
Same as previous question - time for the transition to supplement mode?

This is not something we specify on the datasheet. From tests I can say this occurs within a few ms.

0 Prithvi Raj Narendra1 over 3 years ago in reply to Prithvi Raj Narendra1

Intellectual 550 points

Thanks Anthony for the detailed answer. For the final question, does this mean the supplement mode can't kick in fast enough for GSM 2A surges that last less than a ms?

0 Anthony P Pham over 3 years ago in reply to Prithvi Raj Narendra1

TI__Mastermind 23170 points

Hi Prithvi,

Let me schedule some time in the lab and get some accurate measurements for this.

Best Regards,

Anthony Pham

+1 Anthony P Pham over 3 years ago in reply to Prithvi Raj Narendra1

TI__Mastermind 23170 points

Hi Privthi,

Based on some tests on a single lab bench unit, supplement mode kicks in within 300us.

Best Regards,

Anthony Pham

0 Prithvi Raj Narendra1 over 3 years ago in reply to Anthony P Pham

Intellectual 550 points

Thanks a ton Anthony!

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BQ24079: Transition speed to supplement mode