TPSM831D31: TPSM831D31 Design Calculator and Address Resistor Value

Hello Murali,

Thanks for the clarification. Would you also please share the app note to calculate the input Capacitor for this part.

Hello Murali,

Do we have any app/calculator to calculate the power dissipation of TPSM831D31

1. Input Capacitor

2. Output Capacitor

3. IC 

and IC Junction temperature?

Hello Murali,

Thank you for the inputs. But I have a query relate to Vout_B ripple requirement (20mV). 

My requirement is 

1. 0.8V@10-13A 

2. Vripple- 3mVp-p

3. V tolerance - 3%.

Can you suggest if we can meet the above requirement? Do I need to add any filter circuit and what will be effective value of Ceramic Capacitor and ESR value i should keep? 

Any other suggestion or alternate regulator with 0.5% voltage tolerance (-40 to 105/125 degree w.r.t Ambient temperature).

Your quick response in this regard will be highly appreciable.

Hello Murli,

Can I get the information of Inductor and corresponding other values. Please see the screen-shot.

Hi Kapil,

The TPSM831D31 is a module which includes Inductor in it. You do not need to use an external Inductor.

Hello Murali,

As per the requirement:

1. Rail A- 0.82V@48-55A, Ripple-30mV, Vtolerance-0.5%

2. Rail B 0.8V@8-11A Vripple- 10mV, Vtolerance- 3%

Prepared the schematic, replace 100uF with 22uF, and 470uF with 1500uF.

in rail be do I require 

Would you please review and let me your thought on this? Do i need to add/ remove ceramic/bulk capacitor?

Hi Kapil,

Could you let me know if you are ok to close this as we are communicating by email?

Hello Murali,

The response is bit slow through email. Need to conclude the part and release the design. So if it is fine would you please support? 

Please help here to provide the details of TPSM831D31 part.

 1)Nominal Inductance Value

2)Saturation Current

3)RMS Current

4)Max DCR at 25 Deg.Cel.

We need to estimate above information to calculate the output ESR and capacitance to meet our output voltage ripple specifications.

Hi Kapil,

May I know if you are looking for the details of the Inductor used in the TPSM831D31 module or details of the second stage filter Inductor that I recommended?

Hi Murali,

Please share for both.

Also what should be equivalent ESR value (5x47uF) we need to consider to meet the 10mV requirement?

Can I reduce the ripple by 6mV with this Vout_B= 0.8V by adding more capacitor?

Hello Murali, 

Few queries related to Schematic.

1. What is right approach to keep the bulk capacitor in rail B (0.8V Circuited one)? Do we keep before or after 2nd stage filter?

2. Connection of Sense pin before or after 2nd stage filter? 

3. Placement of  2nd Stage filter close to regulator or close to load?

Regarding the ceramic capacitor, I have taken 22uF (Equivalent ESR 0.12mE) in place of 100uF and compensate the total capacitor including bulk. So it is fine or I need to keep the equivalent Ceramic capacitor w.r.t to reference design for 63A (0.82V) and 11A (0.8V) current rating ? 

Hi Kapil,

1. Bulk capacitor should be placed after 2nd stage filter.

2. Output voltage sensing should be done after the 2nd stage filter

3. Place the 2nd stage filter close to the load.

You can use either 22uF or 47uF ceramic capacitors. However use 0805 package capacitors.

For Rail-B, you can increase the switching frequency to 700KHz as the full load current of this rail is 11A only. Increasing switching frequency helps in reducing the Inductor ripple current and results in lower output ripple for a given output capacitors at output (or reduces output capacitance to meet a given output ripple).

Most likely you may not need 470uF/220uF bulk capacitor at output as the full load current is 11A only, but leave a footprint option on PCB.

Thanks for the clarification Murali. 

Would you also share the inductor data of the for Module for both the voltage rail well? 

Need to do the calculations for different output voltage, Current and ripple requirement.

 1)Nominal Inductance Value 

2)Saturation Current

3)RMS Current

4)Max DCR at 25 Deg.Cel.

Query related to Recommended operating conditions for the input and output Ceramic Capacitors.

As per the Ceramic Capacitor requirement for input and output section, should I keep the recommended values?

1. For input- 500uF

2. Output Rail A- 1200uF

3. Output Rail B- 400uF

or Should I keep the values as per ripple/power requirement for input and output rails? I think I should keep as per ripple/power requirement. 

For 0.82V@63A  I have taken 12*22uF (Ripple value 30mV).

For 0.8V@11A  I have taken 4*22uF in first stage and 10*22uF for 2nd stage filter(10mV).

Please clarify.

and Input Side 17*22uF (ripple 120mV-200mV)

Hi Kapil,

I have provided the Inductor value by email. The Inductor value is enough to estimate the ripple current.

You get the performance shown in the datasheet and Evaluation Module user guide if the recommended capacitance is used. If your application demands much lesser current, then you can reduce the bulk capacitance, but leave the ceramic capacitance as recommended in the datasheet as long as the same switching frequency is used.

As the full load current of Rail A and Rail B are much lower than what TPSM831D31 module can support, I recommend to operate Rail A at 600KHz and Rail B at 700KHz. This further saves the amount of input and output capacitance needed.

In general, estimate the ceramic capacitance needed based on steady state ripple specification and bulk capacitance based on load transient specification.