L6208 REPLACING GS-D200S

[harmony_james]

Posted on May 11, 2013 at 21:44

I am working on developing a board to replace the ST GS-D200S with the L6208 for a pre-existing application. I have already designed and manufactured a small amount of boards for this purpose.

I can't seem to get the proper torque out of the motor I am using (datasheet below). The system is running at 2A and 24V. I am not sure of the driving frequency. Also, when the motor is running correctly (although with low torque) it will intermittently seize up and make a grinding noise. I used the suggested component values for the charge pump. My current sense resistors are .3 OHMS/2W. I have a voltage divider of 10k and 1.15k supplying the Vref's which gives a ref voltage of approx. .515. I know this seems like very limited information but if anyone can provide any help I would greatly appreciate it. The specific motor is the HY200 2215 0220 AX04 Motor Datasheet: http://www-app.etsit.upm.es/departamentos/teat/asignaturas/lab-ingel/mpap_hy_lab.pdf #l6208

[Enrico Poli]

Posted on May 14, 2013 at 10:35

Hi,

I think the problem is the power dissipation. The GS-D200S is a module (each full-bridge is on a different silicon IC) with a huge package which guarantee an excellent power dissipation.The L6208 is a fully integrated device where the two half-bridges are on the same IC with a smaller (and less efficient) package.In conclusion, the L6208 cannot sustain the load current of 2 A for each bridge for a long time. In my opinion you have two options:- Add an external heat sink decreasing the thermal resistance- Reduce the load current (consider that the power dissipation is proportional to the square of the current)

[harmony_james]

Posted on May 14, 2013 at 20:08

Hi Enrico,

Thanks for the reply. Adding a heat sink shouldn't be a problem, I left sufficient room on the board for mounting a large one. Can you answer these two questions for me... In the GS-D200S module the oscillator frequency can be lowered by adding a capacitor between OSC and GND. In the data sheet this frequency is calculated as.... Cf= 80.5-4.7fc/fc =nf (where fc = khz). I know that in this application the capacitor value used is 4.7nF. Can you tell me what frequency you believe this to amount to (I calculate 8.56kHz). Then with that information can you tell me what values you think would be appropriate to achieve the same frequency with the L6208N given the motor being used (see original post for datasheet). Thank you very much for your help.... 

[Enrico Poli]

Posted on May 24, 2013 at 14:29

Ok, first of all the L6208 uses a different control method than GS-D200S.

The L6208 implements a fixed off time PWM control which does not allow to obtain a contant switching frequency.In any case you can obtain a switching frequency of about 8.56 kHz setting the off time (0.6 x R x C) equal to about the 90 % of the target period (about 105 us).A RC network composed by a 10 nF cap e a 18 kOhm resistor should fit your needs.