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TPS780330220 - LOAD TRANSIENT RESPONSE and Current Consumption

Other Parts Discussed in Thread: TPS780XXEVM-301

Hi,

The load transient response is not like shown in the datasheet. I have checked it with the TPS780xxEVM-301 and on my board. When I am trying to pull 10mA I get a drop 215mV and not 100mV like shown in the TPS780xxEVM-301 datasheet. When I am trying to pull 100mA I get a drop 655mV. How can I get better performance? Is there somthing checked that I can use?

When checking the current consuption of the TPS780300250DRV with 0mA load current (open output) when I reach lower input voltages than 3000mV the input current rises to around 6uA. Is it a normal measurment?

 

Thanks.

  • Hi Ziv,

    Can you let us look at your schematic and perhaps any waveforms that you have captured?  What is your output voltage and input voltage? Certainly what you are seeing does not seem correct.  Where are you seeing the 100mV offset accuracy in the EVM User Guide? 

    Bill

  • Hi Bill,

    I have tested the TPS780xxEVM-301. In the datasheet of the TPS780330220(the IC not the EVM) shown the 100mV offset(page12, figure 47).

    VIN = 3600mV, EN = 'HIGH', VSET = 'LOW', VOUT = measured; U2 = TPS780330220DRV, C3 = 3.3uF, C4 = 4.7uF

    1. Load Transient:

     

    Load current is changed from 0mA to maximal value as shown in table below:

     

    Load Current

    Output Transient Voltage Drop

    Output Steady-State Voltage

    (mA)

    (mV)

    (mV)

    10

    215

    3345

    20

    300

    3345

    30

    370

    3345

    40

    423

    3335

    50

    475

    3335

    60

    513

    3335

    70

    558

    3335

    80

    593

    3330

    90

    630

    3330

    100

    675

    3330

    110

    713

    3330

    120

    748

    3330

    130

    795

    3330

    140

    830

    3328

    150

    868

    3328

    2.Current consumption with 0mA load current (open output):

    VIN

    VOUT

    IIN

    (mV)

    (mV)

    (uA)

    4200

    3075

    0.5

    4100

    3074

    0.5

    4000

    3074

    0.5

    3900

    3074

    0.5

    3800

    3073

    0.5

    3700

    3073

    0.5

    3600

    3073

    0.5

    3500

    3073

    0.5

    3400

    3072

    0.5

    3300

    3071

    0.5

    3200

    3070

    0.5

    3100

    3066

    0.5

    3000

    3000

    5.8

    2900

    2900

    5.9

    2800

    2800

    6.0

    2700

    2700

    6.1

    2600

    2600

    6.1

    2500

    2500

    6.1

    2400

    2400

    5.9

     

     Thank you.

     

     

  • Hello Ziv,

    I am still looking at the transient response. 

    It is true for many linear regulators that when the Vin voltage decreases to approach the output voltage (within the dropout voltage, Vdo) the quiescent current will increase dramatically, as you have discovered. When the Vin has decreased into dropout you can imagine that the drive circuitry is saturated to one extreme as the LDO falls out of regulation.

    Bill

  • Hi Bill,

    Is there any thing new with the transient response?

    Thanks,

    Ziv 

  • Just a comment ...

    The output voltage transient voltage drop due to a fast rise or fall (step) in output load current is dependent on several factors:

       output capacitor value

       output capacitor ESR value

       slew rate of the load current step

       response time of the LDO control (feedback) loop (i.e. bandwidth)

    The referenced typical performance curve (i.e. Figure 47) states 10uF for Cout.

    All other factors being the same, a smaller Cout value will cause a larger transient voltage drop.

  • Hi Donald,

    How can I get the performence seen in figure 47? Adding a 10uF capacitor didn't solve the problem.

    Tnx,

    Ziv

  • Reminder:

    Hi,

    How can I get the performence seen in figure 47? Adding a 10uF capacitor didn't solve the problem.

    Tnx,

    Ziv

  • Hi Ziv,

    Here are a couple of things you can check. The voltage rating of the output capacitor should be double or more than that of the output voltage. DC biasing of the output capacitor may be yielding an effective capacitance of much less than 10uF. Next, the attached image shows that your input voltage is 3.6V while the input voltage in the datasheet is higher. As you approach dropout, transient response will likely degrade. Lastly, short, twisted leads from the input power source to the input of the EVM is desired. Otherwise, you should add a large bulk, electrolytic capacitor at the input leads of the EVM to conteract any long lead impedances.

    Regards,

    Darwin

  • Hi Ziv,

    I have same question as you asked here, the load transient performance is way worse than the figure 47 in TI datasheet. did you finally get the chip work as figure 47 or you change the chip?

    Best Regards,

    David Sun

  • Hi David,

    Unfortunitly didnt get to the spec specified in the Datasheet.

     

    thanks,

  • I don't feel very bad because I am not alone.

    Thank you,