TPS74201 LDO

Hi,

Theoretically, the design that you suggest should work if the Vbias voltage is 1.4V above the Vout voltage.  You can see this illustrated in Fgure 9 of the data sheet where for a maximum junction temperature, Tj, of 125degC the Vbias-Vout must be approximately 1.4V or more.  Please note however that when the LDO enters into its dropout region it is just barely regulating the output voltage, and more to the point, the ac performance is greatly diminished. 

Regards

Bill

Hi Bill:

thank your infomation~

1.Please refer to MP2030 the page.2,  About describes (θJC ....8 °C/W ) in Thermal Resistance

Each capacity places whether to need the special attention (in , out , ss, bias....)

0741.MP2030_r0.91.pdf

Hello Ou Gareth,

I do not know what is your question?

You should be very concerned about the amount of power/heat being dissipated in your LDO.  When I layout the pcb I fill the thermal pad, that is under the part, with small vias connected to lower plane layers of copper for sinking, or spreading, heat away from the part.  I recommend connecting the thermal pad to multiple internal plane layers as well as to a bottom surface layer.  In my opinion the copper plane area should add up to 4square inches minimum - and most of this plane area should be concentrated directly under the part. In other words 1square inch of copper on four layers under the part would be better than one 4square inch copper plane of 1oz copper.  Surface copper is better at spreading heat than internal copper layers.

The power dissipated is Pd = (Vin - Vout) x Iout, approximately.

A great help in planning your layout is the new PCB Thermal Calculator tool at the Texas Instruments website: http://www.ti.com/adc/docs/midlevel.tsp?contentId=76735

Select the device and the package (if it is available) : TPS74201RGWR for example

This calculator tool will basically tell you how much total copper you need for your application in both cases for both parts (since they are similar).

Sorry~ edits has the problem

I also have some questions to need your help

1.Please refer to MP2030 the page.2,  About describes (θJC ....8 °C/W ) in Thermal Resistance , I think should be Junction-to-case (bottom) thermal resistance…right ?

Hi

Please let me know if the IC will do the switch or transient after  TPS74201 power up?
Because the IP-RADIO(noise-sensitive ) signal will be interference and repeat reset.