L298 H-bridge

[adrianvon]

Hi all,

I am using the L298 IC to control a 12V 2A motor. If i connect the circuit as shown in the attached diagram, will it work ok? and what fly-back diodes do you suggest? (in the datasheet it say it must be 'fast recovery elements (trr 3 200 nsec) that must be chosen of a VF as low as possible').

Another question, if the enable pin is set to 0v when the h-bridge is not in use, will it consume less current?

Thanks is advance.

 

[ronv]

You can use a small schottky diode like the 1N58XX type. Yes, when not enabled it only draws 6 ma.

 

[adrianvon]

Thanks for your reply.

From the datasheet i can see that the 1N58xx can handle 1A. Is that ok to use for my 2A motor?

Thanks.

 

[ronv]

Yes, should be ok. Notice the peak current is 25 A. 1 A average. The maximum current in the diode occures at 50% of the pwm so the current is about 1A and only 50% of the duty cycle. So the diode current is only about 1/2 A.
The picture shows it better than the words.

 

[audioguru]

The datasheet for the L298 shows that with a motor current of 2A then the saturation voltage loss at the motor can be as high as 5.0V so with a 12V supply then the motor gets only 7V.
Will your motor produce enough power with a supply of only 7V?

 

[adrianvon]

Hi,

Thanks for your replies.

The datasheet for the L298 shows that with a motor current of 2A then the saturation voltage loss at the motor can be as high as 5.0V so with a 12V supply then the motor gets only 7V.
Will your motor produce enough power with a supply of only 7V?

Can i increase the supply voltage to 17V to compensate for the voltage loss??

EDIT: The datasheet shows that the 5V drop is when Vs is 42V. Can it be that the voltage drop is less when Vs is 12v??

 

[adrianvon]

Another question, it it normal to have approx 0.5V on the ground rail when the h-bridge and motor are active?

 

[audioguru]

Another question, it it normal to have approx 0.5V on the ground rail when the h-bridge and motor are active?

Pin 1 and pin 15 are pins that can have current-sensing resistors to ground. Your resistors are 0.5V/2A= 0.25 ohms.
Don't use the resistors if you don't want their voltage drop. Then connect pin 1 and pin 15 to ground.

 

[adrianvon]

Hi,

Another question. The datasheet states that:

Turn-On and Turn-Off : Before to Turn-ON the Supply
Voltage and before to Turn it OFF,the Enable input
must be driven to the Low state.

Why is this? and will i damage the h-bridge if i do not follow this step?

 

[alec_t]

Why is this? and will i damage the h-bridge if i do not follow this step?

The datasheet doesn't show it but the IC AND-gate logic may have a protection diode on the Enable input pin. If so, having the pin High when the supply voltage is Low could cause damaging current to flow through the diode.

 

[ronv]

I may be wrong but I think I have seen that the chip can glitch the output on power up and down if it is not disabled.