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Part Number: TPS2491
Tool/software: WEBENCH® Design Tools
i like the TPS2491 Power Limiting feature, because sometime Current limit is not enough protection.
i would like to use the TPS2491 in a 1275D/E Surge protection.
the 1275 standard requires accomodating with +/-7V around the 28V, frequency 50Hz-200KHz
my question is : does the TPS2491 knows to handle also this "AC" signal. becuase the data sheet assumes all voltages are DC.
What is the response/behavior of the TPS2491 under Voltage Input with Quite high ripple ?
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In reply to Rakesh:
In reply to amos barash:
thanks for trying to help.
i have to admit, i graduated 31 years ago, i forgot a lot of theory, since i did not use it. but i am stubber and trying to learn and remember.
will you be kind to explain me, why a ripple in VIN will cause excessive power consumption.
let me mention that my load is not resistive, it is an active load consuming a constant power, so if the Vin is in Peak (because of the ripple,) than the active load will draw less current, because it is a dc/dc.
so why a peak in Vin due to ripple will cause excessive power consumption: The Vin will be higher, but the current will be lower. The FET is suppose to be ON with low RdsON, and Vout suppose to track Vin, and the FET Gate Voltage suppose to track Vout and Vin + 14 to 16V
my question is also does the the charge pump for the FET Gate is capable to track the Vin and Vout (since the FET is ON with very low RdsON). because the mil-std-1275d specifies Vin as 28V with ripple +/-7Volt at frequencies range 50Hz to 200KHz. in the tps2491 no frequency specification are given.
thanks for your effort to help.
you are right, what you describe is one of the reasons and maybe the main reason for power dissipation over the FET.
The dc/dc has in the input capacitors that try to keep the voltage stable. this means there will be developed a potential difference between the Source and drain of the FET, called Vds.
and Vds x I is power dissipation over the FET.
i have come to a conclusion that the only way (and the safe way) to supervise the FET Heat and to protect it is by using a thermistor mounted on the Thermal PAD of the FET. and any other solution like TPS2491is not good.
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