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TLV757P: TLV75715P Voltage drop

Part Number: TLV757P
Other Parts Discussed in Thread: LP38842-ADJ, LP38842, LP5912, , TPS746, TLV759P, TPS745, TLV755P

Dear Sir/Ms.

What does this form mean?
Is it necessary to maintain Vout on the meter, Vin must be greater than the voltage on the meter?
For example, if Vout=1.5V, Vin must be >2.3V (1.5V+0.8V).

My customer's application is Vin=1.8V, Vout=1.5V, Max Iout=0.5A~1A.

Best Regards,

Kami Huang 

  • Hi Kami,

    You are correct. The dropout voltage is the minimum headroom (Vin - Vout) required by the LDO to keep the output regulated. Using this device with Vout = 1.5 V at a junction temperature of up to 85 C requires a minimum Vin = 1.5 V + 0.8 V = 2.3 V. If the junction temperature will exceed 85 C, the minimum Vin = 1.5 V + 0.85 V = 2.35 V.

    The LP38842 or LP38842-ADJ are ultra low dropout regulators that may be suitable for your customer's application based on the input, output and load requirements. These devices have a maximum dropout voltage of 315 mV at 1.5 A load current. Ohm's law can be used to approximate the dropout voltage at 1 A load current. This is because when the regulator operates near dropout, the pass transistor is driven into the linear region and behaves like a resistor. The on resistance of the pass transistor is independent of the load current:

    Ron = Vdo @ 1.5 A / 1.5 A = Vdo @ 1 A / 1 A

    Vdo @ 1 A = Vdo @ 1.5 A / 1.5 A * 1 A = 315 mV / 1.5 A * 1 A = 210 mV

    Thanks,
    Gerard
  • Hello Gerard,
    Thanks for your reply and suggestion.
    My customer design LP5912 and ask question as following.
    e2e.ti.com/.../764708

    so that they consider TLV757P replace LP5912.
    Vin 1.8V /Vout 1.5V / System Load form 0A to 0.3xA.
    Their product is very small (BGA SIP Module), LP38842 package size is to large for SIP module.
    Would you please give me some advice?

    Best Regards,
    Kami Huang
  • Hi Kami,

    The TLV757P is appropriate as the maximum dropout voltage is 850 mV @ 1 A output current. At 0.3 A, the maximum dropout voltage is therefore 850 mV * 0.3 = 255 mV. As such, this device will be able to regulate the 1.5 V output with a 1.8 V input because the headroom (Vin - Vout = 300 mV) is larger than the maximum dropout voltage. Similarly, the TLV755P, TLV759P, TPS745, and TPS746 all have less than 300 mV dropout voltage at 0.3 A output current and are all available in small packages (SOT-23, WSON, or X2SON).

    Thanks,
    Gerard
  • Hello Gerard,
    Thanks for your quick reply.
    My customer design TLV757P for DDR power.
    There are two specifications to be specified.
    1. Dynamic load will be from 0A to 0.3A when controller from sleep to wake up.
    2. Peak Load will rise to 0.5A.
    Will the TLV757P support these specifications ?

    Best Regards,
    Kami Huang
  • Hello Gerard,
    I'm sorry to trouble you.
    If TLV757P can not fit customer's application? Would you please give me another P/N?
    Vin 1.8V /Vout 1.5V
    There are two specifications to be specified.
    1. Dynamic load will be from 0A to 0.3A when controller from sleep to wake up.
    2. Peak Load will rise to 0.5A.
    Best Regards,
    Kami Huang
  • Hi Kami,

    With a peak load of 0.5 A, the dropout voltage of the TLV757P will be too high:

    Vdo @ 0.5 A = Vdo @ 1 A / 1 A * 0.5 A = 850 mV * 0.5 = 425 mV.

    The LDO's dropout voltage at 0.5 A output current must be lower than the application's headroom (Vin - Vout = 300 mV) for proper output regulation. With this in mind, the TLV759P, TPS745, and TPS746 are all options for your customer as they have maximum dropout voltages of 220 mV, 235 mV, and 220 mV respectively at 1.5 V output voltage and 0.5 A output current.

    Thanks,
    Gerard