TPS7A87: and TPS7A88 Configurations

Hi Vibhu, 

When you know then Vin and Vout conditions with load currents, the next step is to evaluate the dropout and the thermals. 

For TPS7A87, the maximum dropout is 100mV, so you don't have a problem with the headrooms ( Vin - Vout). 

For the thermals, the number you should be checking is the ThetaJA, for TPS7A87 and TPS7A88, the ThetaJA is 33C/W. 

The junction temperature needs to be lower than 125C. 

1) TPS7A87: 5V input -> 3.3 V & 3.3 V outputs (0.5 A / channel)

0.85w per channel, the temperature rise is 0.85 x 33 = 28C. IF you use both channels, it would be 2x 28C = 56C. 

You have to add the ambient temperature on top of the temperature rise when calculating the maximum junction temperature. 

2) TPS7A87: 1.5 V input -> 1.1 V & 1.2 V outputs (0.5 A / channel)

0.2w(for 1.1V) per channel, the temperature rise is 0.2 x 33 = 6.6C. IF you use both channels, it would be 13.2C. 

You have to add the ambient temperature on top of the temperature rise when calculating the maximum junction temperature. 

3) TPS7A88: 3.6 V input -> 2.5 V & 3.3 V outputs (1 A / channel)

1.1w (for 2.5V) per channel, the temperature rise is 1.1 x 33 = 36.3C. IF you use both channels, it would be 72.6C.  

You have to add the ambient temperature on top of the temperature rise when calculating the maximum junction temperature. 

Regards, 
Jason Song