TPS55289: Could somebody review my schematic?

Hi Ryan,

May I know what is the application and Vin range, Vout range, max output current?

EXTVCC can connect with VCC or leave floating to select internal LDO.

When FB is selected as external feedback, FB pin needs to connect with resistor divider to determine Vout. When the device is set to use internal feedback, this
pin is a fault indicator output. It needs to connect with VCC through 100k pull-up resistor and when there is an internal fault happening, this pin outputs logic low
level.

BRs,

Bryce

Hi Bryce,

The application is for battery powered pipe leakage sensing.

What is the default configuration for Vout when FB is internal? 5V?

If i calculate Vout for 12V i get 100k R1 and 374 ohm for R2 using 45mV reference voltage but the excel tool calculates R2 as 10k3

I used the equation Vout = 45mV * (1 + 100k/374)

Thanks

Hi Ryan,

What is Vin range, Vout range, max output current? This is very important for review.

Ryan Stephen said:

What is the default configuration for Vout when FB is internal? 5V?

Yes.

In the excel tool, the reference is set as 1.129V. 12= 1129mV * (1 + 100k/11.3k). I don't recommend that you use 45mV as reference voltage. You can use 1.129V or 1.2V.

About the schematic, below is my comments:

1.Remove the MOSFET in SCL and SDA. This may cause noise. When EN=low, device I2C will not communicate, no need to add extra MOSFET.

2.Change the capacitor in DITH pin to 10nF.

3.Recommend to change FSW resistor to 49.9k to set 400kHz inductor.

4.Recommend to add RC snubber in SW1 and SW2. 2.2nF+2.2ohm(1206)

5.Recommend to add two 10uF capacitor in Vin pin. Make sure the 0.1uF capacitor is 0402 and put it close to IC.

6.Did you put the output current sense resistor? I can't not find it. Please connect as below.

7.Did you connect down divider resistor in FB pin?

8.Please provide part number of output capacitors to calculate loop parameters. Recommend to add two more 10uF ceramic capacitors to reduce Vout ripple.

Regards,

Mulin

Hi Mulin

Vin is 3V to 30V

Iout is 100mA  300mOhm current sense

or 500mA   100mOhm current sense

or 1.5A   20mOhm current sense

Vout is 5V or 12V

output capacitor 100SXV18M

Thanks

Hello Mulin

We have realised the footprint is too large, what configuration can we have to have the smallest footprint? What switching frequency do you recommend to still maintain > 85% efficiency?

Thanks

Hi Ryan,

Please refer to this figure. 2MHz, 1uH inductor. 

Regards,

Mulin