Question 1

I have to set both enable pins to high to move the motor with pwm forward or backward. Why?

Accepted Answer

It's because the BTS7960 is a half-bridge, and the design decision was made to break out both pins for each IC. The datasheet for the BTS7960 IC is useful here.

If you read the datasheet, and compare it to the schematic - you'll see that there are three sets of pins, one set for each half-bridge IC. For each, there is a PWM input pin, an _EN pin, and an _IS pin.

The nPWM pins (1 & 2) are connected (via the buffer IC) to the IN pin (input - pin 2) of each BTS7960.
The n_EN pins (3 &4) are connected (via the buffer IC) to the INH pin (inhibit - pin 3) of each BTS7960. 
The n_IS pins (5 & 6) are connected (directly, no buffer) to the IS pin (current sense - pin 6) of each BTS7960.

Thus, we can see that the "enable" pins are somewhat mislabeled, but likely if left unconnected (high impedance), they "float" (or are interpreted by the BTS7960) to be in the LOW state, which means "go into sleep mode" - so they both must be set to active HIGH to keep both sides of the bridge operational. But you only need to pulse one side or the other (input) bridge to control the motor direction. So why was this decision made?

Section 4.3.3 notes that the BTS7960 has an "over-temperature protection mode" that can be reset by bringing the INH (inhibit - n_EN on the module) LOW (put to sleep mode) - so in theory it is possible for a single side of the h-bridge to overheat and go into this mode, which might be detectable by using the current sense line, and if (when you pulse the PWM) you don't get any current - then you know that direction no longer is responding, and you could wait a bit (for the IC to cool off) then drop that line LOW to reset only that side (direction) - if this makes sense...?

But doing both at the same time wouldn't be that big of a deal, either...

But take a look at the next section of the datasheet (4.3.4), describing current limiting: It seems that when current limits are reached for a bridge (and depending on the slew rate, which is fixed on the module, via a resistor attached to the SR pins (see the schematic - the resistors are R4 and R7) - the switching reverses, and the IN pin on the IC (PWM on the module) is ignored - meaning the other MOSFET switch could be active HIGH, and the only way to turn both of them off is to bring the inhibit pin on the IC (n_EN on the module) from HIGH to LOW. Section 4.4.1 also describes more.

Sections 4.4.4 and 4.4.5 are also useful to understand; if you know the status of the current sense output - plus the status of the switch output (HIGH or LOW) - you can use the truth table to determine if you are in an error condition - in which case you can make decisions on what to do, and being able to independently pulse the n_EN pin on the module LOW might be useful.

All of that said, the application circuit example in figure 11 seems to indicate that in a full-bridge situation, you would connect both the inhibit pins and the current sense pins together and feed them into the micro-controller; so it doesn't make sense why, in this module, the designers didn't do the same thing, except for one potential reason:

If you wanted to, you could use two of these modules to control a stepper motor; for a 4-wire stepper, you would use it just like it is - one module per coil (in which case it still doesn't make sense not to tie the pins together). But for a 6 or 8-wire/pin stepper motor, you might want to control each half of the coils separately. In which case you'd also want both the current sensing pins and the inhibit pins to be broken out separately.  I suspect that this is why the pins are broken out separately.

If you only use the module as an h-bridge, you can tie them together, via carefully adding a solder bridge to the backside of the header on the PCB, between pins 3 & 4. Then only one pin would be needed.

Question 2

What is the maximum voltage this will handle?

Accepted Answer

Max 45 volts DC for the motor side, 5.3 volts DC for the logic side

Question 3

Did anyone figure out Current Sensing? It gives me 0 during normal operation.

Accepted Answer

I found the sensing does work, although I needed to add a RC filter (2k, 10 uF) to get any consistent values going into the Arduino ADC inputs.  I also changed the Arduino PWM output frequency default from near 1 kHz up to 31 kHz, that way I don't hear the annoying loud whine from the motor when it's in between 0 and full.

Question 4

How fast can the r_en and l_en be switched back and forth?

Accepted Answer

Looking at the schematic, R_EN and L_EN drive BTS7960 INH pins (#3). The datasheet describes INH input controls the device's 'sleep mode' but does not provide the timing information you need. On the other hand, R_EN and L_EN control two separate chips so your application (code?) could fine-tune device timing somewhat. If your application needs fast switching times you might consider individual high-side/low-side drivers rather than this h-bridge.

HiLetgoBTS7960 43A H-Bridge PWM Drive High Power Vehicle Motor Drive Module Current Limit

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