SPMD250STP

User notes

19/29

Figure 14.

Phase current programming

9.9

Chopper frequency programming

The chopper frequency is internally set to 17 kHz, and it can be changed by addition of

external components as follows. To increase the chopper frequency a resistor must be

connected between Oscillator (pin 8) and Vss (pin 12, see Figure 15). The resistor value is

calculated according to the formula:

Equation 3

To decrease the chopper frequency a capacitor must be connected between Oscillator (pin

8) and Gnd1 (pin 1). The capacitor value is calculated according to the formula:

Equation 4

12

9

1

12

9

1

SPMD250STP

SPMD250STP

Rf

306

fc 17

–

---------------

k

Ω

=

=

where

fc

kHz

=

Rf

18k

Ω

≥

Cf

80.5

4.7fc

–

fc

-------------------------------

nF

=

=

where

fc

kHz

=