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Part Number: TPS40303
Hi, could you help check above questions, tks!
Test question: At a low temperature of -40 °C, IC's soft-start SS and over-current (short-circuit) protection OCP, what are the internal connections and connections? ?--- pls help check Test phenomenon: Products using TPS40303 are experiencing low temperature -40°C startup problems. As shown in the figure below, Vss normally rises to 1.3V in the first stage (1.9ms calibration time) However, in the second stage, Vss rises again to 1.3V and then falls again to 1.75V to start "oscillation," and a 43ms "hiccup" cycle results in the output Vo not establishing a normal output. Test conditions: Vin=12V, Vo=5V, Io=0.8A~3A (light load test NG, full load 16A), typical recommended application circuit. Problem analysis: 1, undervoltage function removed, excluding undervoltage protection caused; 2. Exclusion of over-current protection, the measured starting peak current Ip is only 5A, far reaching the over-current point (32A); 3, Css capacitance increased to 1uF, reduced to 100pF failed to improve; Also try to connect series resistance from Vin to SS pin, increase the starting current, the improvement is not obvious; 4, Bootstrap capacitor Cbt has been debugged, no improvement. The final measure:
1 By adjusting the over-current point, resistor R9 at IC pin 9 will adjust the over-current point from 32A to 46A. 2 or remove resistor R9, no overcurrent (short circuit) protection Solve the problem of bad start, the product starts normally at a low temperature of -40 °C.
Sorry for the delay on our part. I was out on vacation and this fell through. I think you have identified the right fix for this problem by increasing the OCP trip point. Alternatively I would also try adding a series resistor to the high side FET gate or in series with the boot strap cap. You can start with 4.7ohms.
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