Hi all,
I want to use LT3751 to make a capacitor charger.
The datasheet says LT3751 has 2 gate drivers. The maximum voltage of HVGATE is about VCC-2 or the clamp voltage,and LVGATE is VCC.
Here is my setting, clamp is 0V and Vcc is 5V. The HVGATE is shorted to LVGATE, so the total output gate voltage is pull up to Vcc-2 by HVGATE and LVGATE, then pull up to Vcc by LVGATE only.
Because the output current of HVGATE is larger then LVGATE (accroding to the datasheet, Pull-Up Current is 1.5A when LVGATE Inactive and 2.0A when LVGATE active).
So the gate voltage is raising very fast to VCC-2 and then slowly raising to VCC. The LTspice simulation result is show below. The total gate capacitance of the external MOS is about 5~6nF.
Sorry for long explanation, my question is what is the raising time of this waveform.
The raising time in datasheet is shown as below, 10% to 90% is 40ns, is that right???
Because the LVGATE is active, so the maximum gate voltage should be 5V.
Does 90% means 5V*0.9=4.5V ? or 90% means (5V-2V)*0.9=2.7V ?
By the way, i have made a capacitor charge with LT3750A, peak current is 46A and works very well.
The experimental result shows that the gate voltage of LT3750A is not Vcc-2, as shown below
The Vcc is 6V (created from L78L06), yellow line is DONE.
The high voltage from the datasheet of LT3750A is show below, which is different with the experimental result.
Does the gate voltage of LT3751 is the same as 3750A when the HVGATE is shorted with LVGATE.
Thanks for your help.
