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TPS74801: Can we use LDO, TPS74801 for VIN = 1.7V and Vout = 1.5V?

JungChi Liao41
Prodigy 70 points
Part Number: TPS74801
Other Parts Discussed in Thread: TLV758P, TPS7A10, TPS54525

Can we use LDO, TPS74801 for VIN = 1.7V and Vout = 1.5V application? Another words, to have Vout = 1.5V, can I have VIN = 1.7V only? In section 6.5 of its data sheet, it mentions Vin = Vout + 0.3V. The Vbias is connected to 5V. The Iout is 0.3A max. If not, can you suggest one LDO? Thanks a lot.

  • 0
    TI__Intellectual 1200 points

    JungChi,

    The TPS74801 will regulate the output voltage properly based on these conditions, however please note it requires the use of a BIAS rail (secondary supply voltage for the device) which must be sufficiently above VIN in order to operate properly.

    If you do not have access to a secondary supply rail which s sufficiently above the VIN rail, I would recommend looking at TLV758P for this application. This device has 235 mV MAX dropout voltage at 500 mA load, so at 300 mA load 200 mV will be enough VIN-VOUT differential for VOUT to regulate properly. 

    If you do have access to a secondary supply, I would also recommend looking into TPS7A10, which offers very low dropout voltage (90 mV max at 300 mA load). 

  • 0 in reply to Blake Soileau
    Prodigy 70 points

    Hi Blake,

    Thanks for your quick reply. This design do have access to 5V as the bias voltage. My question is how to discern its data sheet correctly. On top of page 7, why does it ask for VIN = VOUT + 0.3V? Please clarify.

    Also, VIN, 1.7V, is output of a TPS54525, so, it might have +-5% tolerance, 1.615V to 1.785V. We're using many TI's switching regulator in our products. So, if LDO is not suitable, I'm fine using TI's switching regulator instead. This coming design would be high volume. So, I would rather be conservative to ensure a right solution, Please advise. Thanks a lot.

    JungChi

  • 0 in reply to JungChi Liao41
    Prodigy 70 points

    Hi Blake,

    May I have an update? Thanks.

    JungChi

  • 0 in reply to JungChi Liao41
    TI__Intellectual 1200 points

    JungChi,

    The comments at the top of the Electrical Characteristics table refer to the general test conditions used to characterize the device over the full operating range (unless otherwise noted in the table). It does not mean that the device will not function and with lower VIN-VOUT headroom.

    Based on the characteristics of the switching regulator being using for VIN (VIN could be as low as 1.615 V), I would recommend TPS7A10 here as the MAXIMUM dropout voltage is 90 mV at 300 mA. This would ensure that the LDO will continue to regulate properly, even at the min VIN that TPS54525 could possibly deliver.

    Please note you will still need to utilize the BIAS rail for this device to achieve this dropout voltage specification.