Need help with finding the electronic schematics

MC68331 Product Summary

It comes in 132-pin PQFP and 144-pin QFP.

I don't know if anyone can provide you the schematics, and if the people who bought you this from should.

However, your board looks relatively simple. It uses an L6201P chip, which is a "DMOS Full-Bridge Driver". If I read correctly, and if this is an L6201, then the specs are wrong. The datasheet says:

- SUPPLY VOLTAGE UP TO 48V
- 5A MAX PEAK CURRENT (2A max. for L6201)
- TOTAL RMS CURRENT UP TO L6201: 1A; L6202: 1.5A; L6203/L6201PS: 4A

That answers one of your questions. No, you cannot drive a 12V DC motor that has a peak current of 5A, and again, if I read correctly that this chip is L6201.

Assuming that you will drive a DC motor, you have to have a regulated power supply rated at a maximum of 48V DC or your motor's maximum rating (which one comes first wins). Because, at a given PWM to the chip at different times, the speed will only be the same if the supply voltages are the same at those times. Let's check this with an example:

Example 1:

Supply Voltage: 30V DC
Motor rating: 30V DC
PWM Duty Cycle: 50%
Effective Speed: 50%

Example 2:

Supply Voltage: 20V DC
Motor rating: 30V DC
PWM Duty Cycle: 50%
Effective Speed: 33.33%

The difference is because of the supply voltage change. Calculate it yourself, 50% of 20V is 10V. 10V is \$\dfrac{1}{3}\$of 30V. So, the effective speed is 33.33%. I guess that answers one more of your questions.

Pin-out:

The green connector on the left is the main power connections. Connect B+ to your supply voltage, GND to the supply GND, M+ and M- to your DC motor in any direction you wish it to turn.

The black male pin headers on the right are control connections. B+ and GND are your supply voltages. EN is the enable input of the chip, which I will come to. RPWM and LPWM are the PWM control inputs for the left side and right side of the bridge, again, which I will come to. Now, at this point, I don't know about CT and VT, but they should be somewhat related to the other IC on the board, LM358.

EN Pin (Cited from the datasheet):

When a logic high is present on this pin, the DMOS POWER transistors are enabled
to be selectively driven by IN1 and IN2.

RPWM and LPWM Pins (Cited from the datasheet):

Digital Input from the Motor Controller

These are PWM inputs from the microcontroller. EN, RPWM and LPWM pins are rated minimum – 0.3 and maximum + 7 VDC. Your 3.3V or 5V microcontroller will work fine. Refer to the datasheet for more info. Here is the block diagram of this chip, IN1 and IN2 are LPWM and RPWM:

Edit after OP brought out something that I've missed:

You are right. L6201P does have an RMS current of 4A. And I was wrong, L6201 and L6201P are not the same. Just to clear things up:

Specs for L6201 are:

2A maximum peak current
1A total RMS current

Specs for L6201P are:

5A maximum peak current
4A total RMS current