I'm trying to control a 12V DC brushed motor (4A with load ) with an H-bridge , TLE5205 datasheet ( 5A , 6A peak , 40V , integrated free-Wheeling diodes ), but when using a 3S1P lipo battery ( 11.1V , 3.5Ah , 25C ), on motor start-up , a voltage drop occour and the h-bridge automatically goes in Undervoltage lockout ( Vs < 6 Volts ), switching off the motor

Actually this is my test circuit ( the same of datasheet ) test circuit

I tried both single 4700uF capacitor and two 4700uF in parallel

Using a 11V ni-mh battery everything works fine. So I guess it's related only on lipo batteries.

If the motor is connected directly to lipo battery , it runs without any problem.

How could I smooth voltage drop , and avoid the h-bridge to go in UVLO ?

I know the h-bridge is going in UVLO because I compared outputs ( which are in tristate ) and Vef with the error table in datasheet : IN1 = IN2 = 0V , OUT1 = Vs/2 , OUT2 = Vs/2 , Vef = 0 ( Error flag circuit is not shown in the picture above )

  • \$\begingroup\$ Measure the motor resistance, turning the rotor a few times and choose the lowest value. Divide 12V by that resistance. That's your starting current. What does your H-bridge do when you pull that current? \$\endgroup\$ – Brian Drummond Sep 26 '15 at 20:38
  • \$\begingroup\$ @BrianDrummond I made a mistake : 4 A is the start current. Under load att full speed it's about 2A. Motor resistance is 2.5ohm , so the start current should be about 4.8A. With a ni-mh battery the h-bridge works fine. \$\endgroup\$ – Forzaferrarileo Sep 27 '15 at 15:41

Are you sure it's an undervoltage condition? I'd also check for a load short - note that in both cases the error flag is set and the voltage across the motor is zero. A 4-amp motor (under load) will draw much more than that on startup, and this may be causing the driver to shut down.

While connecting the motor directly to the battery will cause the motor to run, this may be simply because the battery provides enough current to get the motor going, which reduces the motor current, which allows the battery voltage to climb, which allows more current to the motor, etc.

What you need to do is get a scope and place it across the battery. Set the trigger to 6 volts, then connect the motor. If the scope doesn't trigger, you know that a 6-volt undervolt condition did not occur.

  • \$\begingroup\$ I'll try as soon as possible to trigger 6 volts with a scope. I made a mistake , 4A is the start current , when under load is about 2A. \$\endgroup\$ – Forzaferrarileo Sep 27 '15 at 15:48
  • \$\begingroup\$ @Forzaferrarileo - If running current is 2 A, the peak (on millisecond time scales) is probably a good deal more than 4. \$\endgroup\$ – WhatRoughBeast Sep 27 '15 at 15:51
  • \$\begingroup\$ the driver isn't shutting down for overcurrent ( in this case the error flag is set [ negated ] and all outputs are switched off). In my case the error flag is set , and the outputs are tristated. It can't be a load short because using a ni-mh battery the h-bridge is working fine. I need a lipo because it's discharge current is more constant than the ni-mh battery I have \$\endgroup\$ – Forzaferrarileo Sep 27 '15 at 16:43
  • \$\begingroup\$ @Forzaferrarileo - Based on what you've said, I'd suspect a weak battery, or at least a weak cell in the stack. \$\endgroup\$ – WhatRoughBeast Sep 27 '15 at 17:09

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