HIP4081A High side mosfet slow turn off. - Page 1
Forum section: electronics / projects

author: tomshirvo
author_rank: Regular Contributor
timestamp: May 23, 2017, 11:51:35 pm
content: Good Morning all,I have built a stepper motor driver with two of the HIP4081A chips. I seem to be having a problem with shoot through because the high side N channel MOSFET isn't turning off fast enough.As shown in the "highside switch off" image the purple line is the ALI input drive line from the SN74LS06DR IC. The light blue line is the switching off of the high side mosfet. The dark blue line is the switch on of the low side mosfet.The "highside switch on" has the same colour details as above but with the high side mosfet switching on.I have tried changing multiple sets of resistors in the circuit shown in the other images.Changed the AHO to Mosfet gate from 10R to 5R to 0R and no differenceChanged the Highside Mosfet source to AHS from 4R7 to 2R35 and no differenceChanged the Highside mosfet source to AHB capacitor from 0.1uF to 1uF and no differenceChanged the AHI pullup to 1K2 and 0R and no difference.Changed both the HDEL and LDEL from 270K to 150K and no differenceChanged the ALI drive line resistor from 100R to 0R and no differenceChanged the R51 pullup on the SN74LS06DR to 600R and no difference.I put a load of 115mA on the output "B+ out"The "no load" image shows the same as "highside switch off" but before the load was added.The mosfets used are STP16NF06LI really don't understand why the driver IC can't switch off the highside mosfet at the correct time.Any help would be much appreciated

author: bktemp
author_rank: Super Contributor
timestamp: May 24, 2017, 05:13:48 am
content: Try connecting the bootstrap capacitors directly between AHB and AHS pins, not after the resistor in the AHS line:At turn on, the capacitor is connected directy to source, so the current flows through the ic an the gate resistor.But at turn off, the ic shorts AHO and AHS, so there is also the resistor in the path, making the turn off time longer.

author: Throy
author_rank: Regular Contributor
timestamp: May 24, 2017, 01:09:00 pm
content: What does the source voltage on the high side FET look like?

author: tomshirvo
author_rank: Regular Contributor
timestamp: May 25, 2017, 01:10:22 am
content: Thanks for the replies but I have figured out what has happened.The highside mosfet has a charge pump as it is a n channel mosfet.The drop in the voltage is the switch off of the highside mosfet. Then when the lowside turns on the highside gate drops to ground as the lowside is pulling the source down to ground. I thought it was shoot through but it really isn't.

author: Derek_Fronek
author_rank: Newbie
timestamp: August 04, 2018, 03:55:08 pm
content: I know this is a slightly older post, but if you are still having issues, try modifying the values of the HDEL and LDEL, these control the offset timing for the upper and lower sets of the mosftets. I see you have chosen the value of 270k for these resistors, the datasheet recommends only going up to 250k, this could be the reason you are having these issues.This can be found in the Application Note for this parthttps://www.intersil.com/content/dam/Intersil/documents/an94/an9405.pdfI'm also working my way through making a successful H-Bridge driver with this part and I hope this might help.