TPS2540 Rds On spec

Joseph Fischer

Other Parts Discussed in Thread: TPS2540

IThe TPS2540 data sheet specifies Rds(on) as having a maximum value of 120 mohms. I am seeing considerably higher values .38V @ 1.44 Amps, or 260 mohms. The conditions are Vin=5.0 volts, ILIM0= hi Z, ILIM1=24.9K, ILIM_SEL+Vin. The highest case temperature I am measuring is about 80-82C. I am measuring the voltage right at the pins of the device with simultaneous current measurements downstream at the load resistor. I notice the voltage drop across the switch seems to decrease with temp, contrary to figure 8 in the data sheet. A measurement made within the first second or two of the load being applied to a cold board gave me a reading of .43V @ 1.47A, or 292 mohms.

Is the specification incorrect, or am I doing something wrong?

over 13 years ago

0 Eric Wright over 13 years ago

TI__Mastermind 42795 points

I will try your experiment on an EVM tomorrow. Do you trust your measurement equipment?

0 Eric Wright over 13 years ago in reply to Eric Wright

TI__Mastermind 42795 points

I checked this on the EVM using very short Kelvin type connection to either side of the IC at room temperature. Measurements are shown below:

Iout(A)	dV(V)	R(ohm)
0.106	0.008	0.076
0.500	0.038	0.075
1.005	0.076	0.076
1.503	0.115	0.077
2.002	0.156	0.078

Very close to typical which is 0.073 ohms.

0 Joseph Fischer over 13 years ago in reply to Eric Wright

Prodigy 30 points

Thanks, Eric. I received 4 additional prototypes from production and they were all ok. It looks like there was a problem with the first sample. I'm not sure if I could have damaged it doing current limit testing. I had a 24.9K resistor on ILIM1 and shorted the output two or three times to test the behavior.

I'll keep an eye on this parameter and let you know if I find any others like this.

0 Eric Wright over 13 years ago in reply to Joseph Fischer

TI__Mastermind 42795 points

Keep an eye on the inductive ringing that can occur when performing output short tests. Long power supply or load leads can cause ringing that can exceed the absolute maximum ratings of the device and damage the FET.

Power management

Power management forum

TPS2540 Rds On spec