If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

# PMP11228: PMP11228 - Questions

Part Number: PMP11228
Other Parts Discussed in Thread: TPS55340, LM5157, BQ33100

Hi TIת

I want to use the PMP11228 - Output Current Capacitor-Charger Boost Converter (28V@0.13A) Reference Design.

A few questions:

• Could you tell me how this circuit is working?
• In case i want to change the output voltage, What should i do?
• In case i want to change the output current, What should i do?

Thanks,

Moshe

• Hi Moshe,

Looking at the schematic, there are two regulation loops (diode OR'd by D2/D3). R1, U2, U3A circuits set the constant current until the output reaches a certain voltage threshold set by the U3B circuit in which it'll switch to constant voltage mode.  You can reduce R1 to increase the constant current. The voltage at which it switches to constant voltage can be set by R10. Increasing it will decrease the output voltage while decreasing R10 will increase the output voltage.

These are all set around the FB reference voltage which is 1.229V found in the TPS55340 datasheet. Please let me know if this is clear. Thanks!

• Thanks Darwin!

The constant voltage is very clear according to TPS55340 datasheet.

What is the purpose of R2, R3 and C10?

Do you have any formula to calculate the constant current? I believe the formula will contain R1 and R2 resistors.

Regards,

Moshe

• Hi Moshe,

R2 sets the gain for the INA device (gain=20k/1k=20)

R3 and C10 adds high frequency filtering for noise (you'll notice the gain dropping dramatically for any higher frequency noise).

The circuit sets the constant current voltage slightly below the FB threshold at 1.22V. This ensures that it takes over before the voltage loop kicks in at 28V.

So Iout= (1.22V * 1k ohms) / (Rsense * R2)

I recommend keeping the 20k for R2, setting Iout to the desired current, then solving for Rsense. Let me know if this helps. Thanks!

• Thanks Darwin,

How can i calculate R3,C10 values?

Regards,

Moshe

• Hi Moshe,

The corner frequency of the low pass filter is fc=1/(2*PI*R3*C10). I recommend keeping these two values on your design. Thanks!

• Thanks Darwin!

Do you know TI has any replacement for the old PMP11228?

Do you know if TI has a Power Back-Up Managers like MP5515 (MPS) or ACT4910 (Qorvo)?

Regards,

Moshe

• Hi Moshe,

We have newer devices that can replace the boost controller like LM5157 as an example; and in general, this type of application/approach can be used with newer similar devices if necessary.

Looking at the BOM tool on ti.com (https://bomcross.ti.com/en/), BQ33100 has similar functionality.

Please let us know if this helps. Thanks!