TPS92515: VIADJ offset voltage

Hello Kai,

1)  This is true under certain circumstances.  If you hit minimum on-time the energy in the inductor is 1/2*L*i^2.  If 'L' goes down 'i' goes up since minimum on-time is a fixed value. Since the 'i' term is squared and the 'L' term is not the energy goes up proportionally with 'i'.  Other than your statement is correct since you are regulating peak current.  The 'i^2' stays constant and 'L' drops so the energy will be lower.

2)  This is also true however if switching at lower frequency and trying to keep the ripple constant 'L' has to go up defeating the decrease in average current.  This can be offset by using more output capacitance.

3)  This is partially true.  There really isn't transient time from no switching to switching, if PWM goes high the TPS92515 will turn on the MOSFET until it hits peak current and be in regulation after the first on-time.  If there is output capacitance there can be delay however if you apply a duty cycle of PWM at a reasonable PWM frequency you will get reduced current.

Note that I stated average current, not RMS current.  Calculating current when driving LEDs uses average current not RMS current.  This is because the load is a fixed voltage not a resistor load.

You may want to consider using the TPS92515A instead of the TPS92515 due to the power on calibration circuit.  The benefit of the TPS92515 is a more accurate set-point for regulation.  The Con is that some parts can power up in a different calibration state if close to a bit transition.  This can cause a 5 mV change in offset voltage.  At full brightness it has a more accurate set-point, at low dim levels it can be a noticeable light change during power cycling even though it is a more accurate set-point.  The TPS92515A does not have the calibration circuit which makes the offset error higher but you will not see some TPS92515A change regulation set-point during power cycling.

Best Regards,

Thanks Irwin,

Regarding A version, is it TPS92515AHV-Q1?

Also is only the difference between non A version and A version calibration function?

Regards,
Kai