Problems in Configuration of my L6482 board

[val_ltd]

Posted on March 23, 2014 at 11:37

I have designed a board using a L6482 chip.

My L6482 has started, and I can send and receive messages a través de SPI bus, but now I have a problem: My STATUS register says:

1110 0000 0000 0011

  (Get Status Command = 0xE003). It means:

OCD

= 1  --> overcurrent

BUSY

= 1  --> Stopped

Hiz

= 1  --> Bridges in High Impedance State.

The problem occurs

even

without connecting the

stepper

motor.

...! Just turn on the power, and my L6482 gets quite hot, but I have measured the total current of the board, and it is only 0.1 Amp.

Configuration:

I have read AN4354 and UM1685 Application note and User Manual, in order to calculate config values of my board: OCD_TH = 1000mV

TCC = 1200 nSg

IGATE = 64 mA TBLANK = 500 nSg TDT = 250 nSg I use 3.3v external power supply: VCCREG, VREG and VDDIO are connected to this 3.3v external power supply. I use VSREG and internal regulator for obtaining VCC=15v. VCC pin is unconnected. I am using Mosfets STB75NF75L with D2PAK package, of ST Microelectronics manufacturer. My Rsense =

200mΩ

, is it a too high value? So I think the problem could be:

• Bad values in registers of configuration. (AN 4354, chapter 2.4: Too low gate charge to complete the Miller plateau region...?)

• Bad connections of: Vs, VSreg, Vccreg, Vcc, Vdd, etc.......

Could anybody put here the right connections? And the configuration values? Thanks in advance,

[val_ltd]

Posted on June 26, 2014 at 09:08

Is there a way to make an current limitation, in order to protect the stepper motor?

(I am not talking about the warning and alarm registers, OCD_TH, etc.). I.e. If I use a small stepper motor, what is the way to control the current by the motor, in order to do not exceed 0.75 amperes?

I want to

prevent the engine

can burn

, limiting

the maximum current, but not only by alarms and alerts.

If my motor get too warm because of a too big current, what is the way to control this value? I see that TVAL_HOLD, TVAL_RUN, TVAL_ACC and TVAL_DEC control the torque values, so they also control the current value by the motor. But, what is the relation between them? Modify this values is the right way to control de max. current by the stepper motor? Thanks in advance.

[larken]

Posted on June 28, 2014 at 19:45

Ramirez, the problems you are having are most likly your PCB layout. Having your mosfet place around the board with the control chip in the middle will cause al kinds of stray current arround it affecting the operation.  Yours may look like the eval board, but they may have a hidden layer just for the high currents. Also your main capacitor and incomming power is off to the corner far away from the other bridge, so the path lengths are different.

 I suggest to put the bridge and input power on one side of the pcb, with a common ground and power point exactly center between the 2 bridges. Your 2 sense resistors should connect there and the main cap and bypass cap (.47uf 100v poly) should be all there in a tight close power point between the 2 bridges.  Then beside the  power section put the control L6482 with a thick ground pad going over to the star gound point where the power and sense res connect. Thats the only place where all grounds come from for all inputs and power.   You can actualy get good results from a 2 layer properly layed out hand routed pcb, than a poorly layed out 4 layer.    

[larken]

Posted on July 01, 2014 at 00:44

Here is a mockup of a layout used in some commercial drives.  Also you could put an on board fuse to protect the motor, incase all else fails.

[val_ltd]

Posted on July 01, 2014 at 08:18

Thank so much , Kenny for your support,

I think your proposal could be something like this:

[val_ltd]

Posted on July 01, 2014 at 09:13

I found

another significant difference between my pcb board and ST designs:

In my boards:

With Mosfet 

STB75NF75L it is necessary a Total gate charge: 75 nC V at 5v

With Mosfet 

STB80NF10T4

it is necessary a Total gate charge: 135 nC V at 10v

But in ST design (see EVAL6482H-DISC) they always use the lowest

Total gate charge they find:

With Mosfet 

STL40N10F7

it is only necessary a Total gate charge:

14 nC

V at 10v That way, it is easier for L6482H driver to switch on this Mosfets.

[larken]

Posted on July 04, 2014 at 22:31 You may want to put the l6472 on the on the bottom side closer to the sense resistors so the paths are shorter.  Its important the control chip be close to the sense resistors and that common ground point. You might be able to make the bridges area more compact so the power traces are shorter. The smaller pcb real estate in the power section, the less noise it will generate. Also adding opto couplers for the Step and Direction inputs makes sure there are no ground problems when connecting to the control board.