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Hybrid ICs for Driving Brush-Type DC Motors Slide 15

This is a circuit diagram of the evaluation board of the STK681-332 and 352. Users can set the current limit by choosing the values for R1, R2, R3 and R4. First, set a reference voltage at pin 19, the Vref pin, at some value less than 2.0 V. This voltage is divided internally by 4.9 to obtain the internal voltage that is compared to the voltage across the external current-sensing resistors, R3 and R4. As an example, choose 0.49 V as Vref, by picking R1 and R2 to divide the Vdd of 5 V applied at pin 15 down to 0.49 V. Choosing R1 = 4.51 k ohms and R2 = 490 ohms will accomplish this. Vref is now 490 divided by the sum of 4.51 k and 0.49 k, multiplied by 5 V, and this equals 0.490 V. This is divided internally by 4.9, to obtain the current sensing voltage. In this example, the 0.49 V will be divided by 4.9, and the result will be a sensing voltage of 0.1 V, or 100 mV. The final step is to pick R1 and R2 so that the desired current limit flowing through them results in 100 mV. This can be a single resistor if a proper value is available.

PTM Published on: 2012-11-30