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TPS82085: TPS82085-compare to ISL8205 for 100% duty operation

Part Number: TPS82085

Hi E2E,

          My customer would like to use TPS82085 to replace ISL8205 in their optical module, as ISL8205 has an issue for 100% duty operation.

          Vin is 3.3V and Vout is 2.2V. When Vin drops to 2.2V, ISL8205 operates in 100% duty. Putting Vin to 1.5V makes UVLO turn off ISL8205, but EN pin is still enabled as 1.5V. At this time, recover Vin to 3.3V, ISL8205 is still in 100% duty mode, and Vout=Vin=3.3V. Intersil explained that, when 100% duty mode is triggered, ISL8205 turns on high side FET and ignores output feedback. Only thorough Power on Reset or re-enable it by EN can get it out of this mode.

         Before replacing ISL8205 with TPS82085, they would like to confirm TPS82085 doesn’t have the same operation. Could you pls describe how TPS82085 achieves 100% duty briefly? And, the he difference from ISL8205? I don't think we have the same issue.

BTW, VIN and EN are connected together. If tps82085's VIN and EN re-powered from 1-2V(not 0V) to 3.3V, does it has any other issue?

Thanks.

  • Hi Jerry,

    I can't comment on other vendor's devices and how they work, but we have not had an issue exiting 100% mode in the past.  Here is the TPS82085 entering and exiting 100% mode with a Vin ramp up/down (in yellow) and 2.5Vout (in red) with a 3 Ohm load.  EN is tied to Vin.