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PTH08000WAH Output capacitance

vijetha hn
Expert 1230 points
Other Parts Discussed in Thread: PTH08000W

Hi,

I am using PTH08000WAH for 12V to 3.3 V generation of following configurations.

Vin = 12V

Vout = 3.3V

Cin = 100uF, 25V, 20%,Tantalum and 22uF, 25V,20% Ceramic

Cout = 100uF, 6.3V, 20%, 70mOHM ESR, Tantalum and 100nF ceramic

Radj = 1.87K OHM

My queries :

1. Whether this design works for current requirement of 2A? The voltage deviation expected at the regulator output is 100mV

2. The Cout is 100uF, tantalum with ESR = 70mOHM. Whether this ESR is high for the requirement?

3. Can i go for 300uF ? If yes whether I can keep the ESR same or should I change? if chang, lesser or higher value?

Please suggest me these details.

Regards,

Vijetha

  • 0
    Expert 1230 points
    Also let me know if there is any test web bench or any other option that helps us in selecting the capacitors and their parameters for the IC PTH0800WAH.
  • 0 in reply to vijetha hn
    Expert 1230 points
    Adding to the queries...
    4. There are 4 DSP Ics as load for for the 3.3V net. 300uF of Tantalum capacitor with ESR=60mOHM connected at 3.3V supply pin of each DSP IC. Does this have any effect on transient improvement?
  • 0 in reply to vijetha hn
    TI__Mastermind 38230 points

    Vijetha;

    PTH08000W  maximum output capacitance limits  are located in the product specification :

    In electrical characteristics under external output capacitance  the  following limits apply.

    1. Ceramic capacitance type maximum = 220µF

    2. Non ceramic ( Polarized ) capacitance is :typical = 100µ, maximum = 330µF with ESR = minimum of 14mΩ ( note 6,7) below.

    3. Based upon this application maximum output  polarized capacitance  and (ESR minimum ≥14mΩ )total exceeds maximum limits of 330uf total
    3.3V net. 300uF of Tantalum capacitor with ESR=60mOHM connected at 3.3V supply pin of each DSP IC plus 100uF at 70mΩ directly on Vout bus.

    3a. There appears to be at least either 400uF polarized or 1000uf polarized on the3.3V bus.

    4. The maximum output polarized capacitance limits are exceeded.

    5. The transient variation is typical ±100mv with a 1 amp load step.  The 3.3V DC Voltage variation  is  3% or 99mV at3.3vout.   over line load and temperature variations.

    MY direct e-mail is tguerin@ti.com if you have any additional questions.

    Tom