VNH2SP30 H-Bridge Unexpected reaction to current control

[jorick]

Posted on March 21, 2016 at 12:33

For a project I'm working on I have to be able to switch the polarity of a peltier element (or other device) and be able to linear control the current through the peltier.

I didn't want to put a normal relay in this system do to the mechanical wear, so a H-bridge was the best option. The VNH2SP30 was the best choise in my opinion after reading the datasheet. So the design was made based on this H-bridge.I have made a prototype PCB with this H-Bridge and saw a unexpected reaction to the lineair current control. (The lineair current control is a OPAMP, MOSFET based circuit I have used many times before and this circuits reacts/works as expected on the PCB)When I enable INA, enable the PWM to a DC value so lets say a PWM of 100% and limit the max dc current to lets say 2Adc through the peltier. The Output of the H-bridge will pulse in a PWM-like dutycycle based on the current limit setting I use. The higher the current limit the higher the PWM duty-cycle. When the current reaches maximum that is possible to go through the peltier (at a 15Vdc PSU) the output of the H-Bridge is a stable 100% ''PWM''.After reading the datasheet I was under the impression that it was possible to use this H-Bridge in a DC configuration (with a 0Hz ''PWM''). So my question is, where does the PWM on the output come from? Is this normal behaviour for the VNH2SP30? The signals displayed in the images below are taken when the current limit was set to 2ACircuit: #h-bridge #vnh2sp30

[jorick]

Posted on July 26, 2016 at 10:16

Hello Forum members,

It has been a while since I posted the question above and I haven't had any answers in the past months, does no one have an idea what the cause is of the explained problem?

/content/ccc/resource/technical/document/datasheet/group2/66/b8/f5/2c/9a/66/41/c7/CD00043711/files/CD000437pdf/jcr:content/translations/en.CD000437pdf

I hope someone can give me an explanation so I can get an ease of mind for the made design ;) Thank you in advance! (The design works perfectly for what is has to do but this is a 'small' point I really would like an answer to, just for easing my curiosity as a designer/programmer ;) )

[jorick]

Posted on September 05, 2016 at 14:18

The problem has been solved. Well not the misleading datasheet of the VNH2SP But The design works.

It is possible to run the VNH2SP30 on 100% duty-cycle or PWM-less operation but you automatically get a pulse on the output of the H-bridge. As far as I have tested I couldn't eliminate this pulse. The information on page 10/33 of the datasheet giving the specs of the PWM frequency is incorrect or open to own interpretation. The datasheets states: PWM frequency = min 0 and max 20 kHz. Screenshot of the measurement of OUTA with the highest possible duty-cycle I could achieve. with a pure resistive load. With a peltier as load the H-Bridge still produces it's own pulse with a frequency between 600 - 900 Hz. The problem is still not solved. Do I miss something in the datasheet or.... ?