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 ) 
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 )
Best Answer
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.