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TPS 60402 Isupply vs. Vin

Other Parts Discussed in Thread: TPS60402

Has anyone had a problem with excessive input current (>15 ma) at 1 to 1.5 Vin during startup?  We have measured a narrow "carrot" region where the TPS 60402 draws nearly  20 mA around 1.28 V during startup.  It is unusable in our low power application, which can supply only about 5 to 6 mA.  Would like to use this part because of it's 125 C capability, but it does not seem viable unless the power input can supply 20 mA during startup.  Tested with Cfly and Cout = 1uF; Cin = 4.7 uF, V in = 5V.  Any suggestions?  For now, we're using MAX1852, which starts and runs perfectly, drawing < 100uA at all input voltages.

  • The TPS60402 will have higher input current at Vin=1V to1.5V.  This is communicated on the datasheet's Figure 7.  This is typically not a problem because the TPS60402 specified operating voltage is 1.6V to 5.5V, which is outside the range where the current could be slightly higher at startup.

  • The attached graph shows our measurement of TPS60402 Iin vs. Vin.  It's rather larger than datasheet Figure 7 shows.   In my application (an aircraft fuel sensor), the inverter operates at 5 V from a LDO linear regulator, which is powered from 12 VDC through a large (2kOhm) resistance.  If the TPS60402 actually exhibited the behavior shown in datasheet Figure 7, it would work fine.  At startup, in order to get to the specified operating voltage range, it has to pass through the "trouble range" between 1 to 1.5V.  My application cannot supply the current required by the TPS60402 while the input voltage ramps up from 1 to 1.5V, so the part is simply not suitable for the application.