DRV8801 OCP Issue - Page 1
Forum section: electronics / projects

author: Aleksandar B.
author_rank: Contributor
timestamp: June 20, 2016, 06:26:34 am
content: Greetings everyone,So for a project of mine, I am using TI's DRV 8801 H bridge and found a strange issue with the OCP. The datasheet states that the OCP kicks in when the voltage on the SENSE pin exceeds 500mV, but in my case it kicks in at 100mV.Now the weird part is that the output of the H bridge for current sense is another pin called VPROPI (Voltage proportional to current) which multiplies the voltage from the SENSE pin by 5. I guess this is done to allow for a smaller sense resistor. What bothers me is that the proportion of my error is the same. The OCP kicks in at 5x less than it should. On the other hand, it makes no sense for the VPROPI pin to be saturated at 500mV...The issue exists on all of my boards (around 30 H bridges).I have asked TI's support and they told me to ask my distributor for support because "we (TI) are less technical but sometimes we can help out". So I asked Farnell, who apparently has an "internal link with a team of TI dedicated engineers for technical support", but got no answer.Has anyone encountered similar issues with the OCP on TI devices? Or am I missing something entirely.

author: CM800
author_rank: Frequent Contributor
timestamp: June 20, 2016, 09:46:38 am
content: "we (TI) are less technical but sometimes we can help out" That sounds absolutely hysterical, the MANUFACTURER of many advanced semiconductors, designers of the dev / prototype boards etc... are less technical?...... what?Sounds like a case of Lazy.I was actually really looking at some of their microcontrollers... but with that kind of stuff being batted about.... nuh-uh.

author: danadak
author_rank: Super Contributor
timestamp: June 20, 2016, 10:49:47 am
content: You are conforming to the points made in 9.3.11 and using a.2 ohm (from datasheet, for 500 mV typical trip) ?Regards, Dana.

author: Aleksandar B.
author_rank: Contributor
timestamp: June 20, 2016, 11:29:17 am
content: Quote from: danadak on June 20, 2016, 10:49:47 amI am using an 1 Ohm resistor on the sense pin because the current on the motor is not high.

author: bdeianov
author_rank: Contributor
timestamp: April 30, 2020, 04:43:53 pm
content: Quote from: Aleksandar B. on June 20, 2016, 06:26:34 amDid you ever figure this out?I'm using the DRV8801 for a project and trying to work out the best VPROPI/SENSE setup. 1 Ohm sense resistor sounds about right for my application as well. My current prototype uses a breakout board from Pololu which includes a 0.1 Ohm sense resistor. Not sure why they did that as it makes the VPROPI level unusably low for low powered motors.

author: thm_w
author_rank: Super Contributor
timestamp: April 30, 2020, 09:42:38 pm
content: Quote from: bdeianov on April 30, 2020, 04:43:53 pmThe chip is designed for +/- 2.5A, so they'd expect you to be using a motor that takes a bit of current. Not that you can't use it for that of course. 1R = 6W dissipation at 2.5A, which is too high.Swap the resistor for 1R and let us know how it works.

author: bdeianov
author_rank: Contributor
timestamp: April 30, 2020, 10:17:49 pm
content: Thanks for the reply. Yeah, makes sense to design for the high current case, but Pololu could have at least used a 0.2R per the spec sheet and still have full capability but double the sense resolution.My motor uses 50mA typical, 100mA max. OCP is supposed to cut off when the sense voltage reaches 500mV (and the original poster was seeing even less, I wonder why), so with a 1R resistor that's a max current of 500mA and max power dissipation of 1/4W. At 50mA current, I should see 250mV on VPROPI instead of the 25mV I see now. I'll try and report back.