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Problem with PTH08T230W

Lukasz Kolaszewski
Prodigy 110 points
Other Parts Discussed in Thread: PTH08T230W

Hi,

I'm trying to use power module PTH08T230W. Application has been made according to product data sheet. Pins connection is:
1 - SYNC - tied to GND
2 - Vinput ( 10 V )
3 - GND
4 - Vo ( ~5.5 V )
5 - +SENS - shorted to Vo
6 - -SENS - shorted to GND
7 - Vadj - connected with GND via 5.6 OHm resistor
8 - TT - connected with Vo via 47 kOhm resistor
9 - Track - shorted to Vi
10 - Inhibit - left floating

Input capacitors bank is: 2 x 100 uF / 16V (ESR = 100 mOhm , tantalum) + 1 x 100 uF (ceramic) + 1 x 22 uF (ceramic)

Output capacitors: 1 x 100 uF / 10V (ESR = 80 mOhm, tantalum) + 2 x 100 uF (ceramic) + 1 x 22 uF (ceramic)

My target configuration is 10V input, 5.5V output with 4A of current. When input voltage is applied module is not working. Output voltage is ~ 0.2 V and just after few second temperature rise up to 70 ' C. Current consumption is ~400mA @ 10V. Inhibit pin is left floating but after shorting to GND nothing happens. Module not response. I've checked all connections on PCB, ereythign is correct (according to data sheet). What am I doing wrong? Have you got any sugesstions?

Best regards,
Lucas

  • 0
    TI__Mastermind 38230 points

    Lucas:

    I revewed the details sent on the TT turbo trans function versus out put bus capacitors.

    The turbo trans(TT)   selection and function is based upon the ESR of the polarized output capacitors. "Output capacitors: 1 x 100 uF / 10V (ESR = 80 mOhm, tantalum) + 2 x 100 uF (ceramic) + 1 x 22 uF (ceramic)" The ESR  is too high ( 80mΩ)  for this design plus the 5.5Vout must not have any Turbo trans (TT) resistor ( there is 47kΩ) .

    First remove the 47kΩ TT resistor as the module is oscillating due the TT resistor.The module  due the incorrect TT may have been overstressed by over heating

    Regards

    Tom Guerin

    630-836-2828

    Call me and we can discuss this question

  • 0 in reply to Tom Guerin
    Prodigy 110 points

    Tom, thanks for your reply. I'll let you know if your sugest is helpfull.  My question is why I need to remove TT resistor? As i read data sheet there is table with TT resistor value vs. output capacitance. I choosed 47 kHz which is connected with value 330 uF. Second question is why this ESR value is to high? 80 mOhm parallel with two ceramic is lower than ~30 mOhm, is this still to high?

    Lucas

  • 0 in reply to Lukasz Kolaszewski
    TI__Mastermind 38230 points

    Thanks for th e-mail. The 80mΩ ESR is too high  to be considered    a turbo trans function features. The typical  TT ESR is to be 15 mΩ  or less on any polarized tantalum capacitors. This shown in both capacitor selection and fast transient sections.

    The 2x100uf ceramic capacitors presently in this application state turbo trans resistor is open(Type B TT section ) . The power module is thermally  active as it is oscillating with the 47kΩ TT resistor and no effective increased capacitance. . In voltages greater than 3.6V, The  turbo trans function has  a minor transient effect on the output  voltage  .

    A 5.5V load step of 2 amps has a impact of 115mV on the 5.5V regulated output voltage . This translates to a 5.5V variation  of 5. 38V volt deviation  with is  load step.

     

     

  • 0 in reply to Tom Guerin
    Prodigy 110 points

    I've removed TT resistor (TT pin is floating) and nothing has changed. Module is still overheated, output voltage is ~0V. TT pin voltage is ~2V. Any ideas what next?

  • 0 in reply to Lukasz Kolaszewski
    TI__Mastermind 38230 points

    Luc:

     

    I would need to discusss this application with you. Can you call me at 630-836-2828?

    Tom

  • 0 in reply to Tom Guerin
    TI__Mastermind 38230 points

    Luc;

    I attached the TT work sheet. Can you measure the output bus resistance to ground.? It is possibly an external short.

    The link to the turbo trans calculator is:

    http://focus.ti.com/analog/docs/turbotranssearch.tsp?familyId=561

     

    Based upon the TT calculator  there is no TT resistor when using the 80mΩ ESR , 100UF capacitor.