L6474 Charge pump low...only 5 volts

larken · ‎2014-06-25

Posted on June 26, 2014 at 03:57

I'm builting a mini drive using the L6474. Got it all working and it runs smooth, but the driver runs very hot and I measured the charge pump and the voltage is only 5volts p-p max (manual says it should be 10vp-p)

The pump is running about 900K-1mhz but only swinging about 5 volts. and when the motor is running slow, it goes as low as 3 .5 volts.

The slower you spin the motor the hotter it gets, (very hot, over 100C) and when you speed it up it runs cooler. Im guessing the upper mosfets aren't being fully turned on, generating the heat.

Any ideas ?

Enrico Poli · ‎2014-06-30

Posted on June 30, 2014 at 17:21

The chatge pump frequency you measured seems too high. This is probably the cause of the overstress of the circuitry.

Are you using an external clock source? If possible, can you measure the clock frequency through the OSCOUT pin?

Enrico

larken · ‎2014-06-30

Posted on July 01, 2014 at 00:58

Thanks

I'm running the internal osc but i will measure the freq.

I did switch to this diode RB160M-30CT-ND (digikey pn)

and it gained a few volts, but still runs very hot

Without any C-fly connected (0.01uf) , it does swing to 10V ac , but when put in the circuit , loads down to produce a voltage (above + rail) of 7vdc when spinning fast and 5vdc when motor is holding.

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Enrico Poli · ‎2014-07-07

Posted on July 07, 2014 at 09:38

Ok. Can you share the configuration of the IC?

Did you check if the power outputs are commutating at high frequency?

Enrico