Question of TPS22810

Hi Nishizawa, 

Thanks for reaching out on E2E! Please find the answers to your questions below.

1:

The calculation between RPD and thermal temperature depends on the thetaJA value of the package, so you first need to determine what that number is from table 7.4 in the datasheet. From there, you need to figure out the total amount of current flowing into the QOD pin. This is the output voltage divided by the internal QOD resistance + external QOD resistance. You then take the squared current, multiply it by the internal QOD resistance, and multiply that by the thetaJA number. This will give you the expected temperature rise in the device.

As an example, if the output voltage is 12V, there is a 300Ω external QOD resistance, and the DBV package is being used, then the total current into the QOD pin is:

QOD Current = VOUT / (External QOD + Internal QOD)

QOD Current = 12V / (300Ω + 265Ω)

QOD Current = 21.2mA

The total power dissipated in the device will be:

Power = I^2 x R

Power = (21.2mA)^2 x 265Ω

Power = 119mW

This will give the following temperature rise in the device:

Temperature Rise = Power x ThetaJA

Temperature Rise = 119mW x 182°C/W

Temperature Rise = 21.7°C

Therefore, as long as the ambient temperature is below 103.3°C, the device will not exceed the junction temperature of 125°C.

With large output capacitance, the duration of this event could be longer. However, as long as you choose a resistor value that keeps you below the maximum junction temperature, you should be fine.

2: There is not maximum capacitance value on CT. If you choose an extremely large value, the rise time of the device will be longer.

Thanks,

Arthur Huang

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