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TPS62742: ILOAD current vs Iout

Part Number: TPS62742
Other Parts Discussed in Thread: TPS62740,

I have an application where the MCU is using very little current (generally <1mA), but there is a separate subsystem that uses a lot more current, including an RF chip. This subsystem only needs to be on <10% of the time, and therefore can be switched off by the MCU. Currently I am achieving that with 2 voltage regulators, but I am very interested in combining the functionality of both in this single PMIC. But for some reason, I see in the data sheet that Iload can only be max 100mA, even though the total Iout can be 300 or 400mA (TPS62740 vs TPS62742). To me it makes no sense that a chip that has a switch to enable/disable a separate Vcc subsystem, is only able to supply 25%-30% of the max output current on that output. To me it makes sense that that separate subsystem is actually the most power hungry part of the total circuit, not the least power hungry. So what will happen if I draw 150mA from the Iload for <1s on a regular (every 10 minutes) basis? Is there a chip that allows this functionality with a higher Iload?

  • Hello Dolf,

    The buck converter can support 300mA/400mA because of the power dissipation shared between the high-side and low-side FETs. However, all the current will pass through the high-side FET on-resistance (RLOAD). Hence, the LDO load current is limited to 100mA.


    Forcing a load current on the LDO over 100mA might result in output voltage going out of regulation. If the LDO load can accommodate a relaxed supply voltage range, it can potentially support the 150mA load. You can use the graph in Figure 5 to calculate the voltage drop on LDO so you can have an idea of the expected VOUT. Add some tolerance to predict the worst-case condition.

    Best regards,

    Excel

  • Hello Dolf,

    Do you have further questions? If not then, I will close this thread. You can post your queries to re-open the thread again.

    Thank you.

    Best regards,

    Excel