LM5170-Q1: LM5170-Q1 Design Calculator (ZIP630KB ),07 Dec 2016 Results do not match Datasheet.

Kipton Moravec

Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5170

Equation 14 and 63 in the LM5170-Q1 Datasheet says:

RRAMP = 9.6 / (FSW * CRAMP) = 9.6 / (100000 Hz * 0.000000001F) = 96000 Hz

However in the LM5170 Design Calculator if I put in 100 kHz in Selected Switching Frequency (Cell B21) and 1 nF in Selected RAMP Capacitor (CRAMP1, CRAMP2) (Cell B62)

Calculated RAMP Resistor (RRAMP1, RRAMP2) (Cell B63) is 100.00 kOhms.

Why is it not 96 kOhms?

over 8 years ago

0 Youhao Xi over 8 years ago

TI__Guru* 78190 points

It is already noticed and a fixed is underway. The info in the datasheet is correct: RRAMP=96 kOhm. Thank you.

0 Kipton Moravec over 8 years ago in reply to Youhao Xi

Expert 1545 points

How about this one:

Problem with the UVLO calculations The Calculated Hysteresis Resistor is a negative number, and wrong if positive.

0 Youhao Xi over 8 years ago in reply to Kipton Moravec

TI__Guru* 78190 points

2.6V is not a valid input when you select 130kOhm. There is 25uA current source to achieve the UVLO hysteresis: Vhys = RUVLO1 x 25uA = 130kOhm x 25uA = 3.25V, already greater than 2.6V. RUVLO3 is only needed to provide additional hysteresis if RUVLO1 is not large enough. If you want 2.6V hysteresis, you need to reduce RUVLO1, of course you need to reduce the RUVLO2 at the same ratio, and you do not need the additional hysteresis in your case, so your Ruvlo3=0.

Thanks,

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LM5170-Q1: LM5170-Q1 Design Calculator (ZIP630KB ),07 Dec 2016 Results do not match Datasheet.