TMC246_06 Datasheet, PDF (18/26 Pages) List of Unclassifed Manufacturers – High Current Microstep Stepper Motor Driver with sensorless stall detection, protection / diagnosis and SPI Interface

TMC246 / TMC246A DATA SHEET (V2.03 / Nov. 6th, 2006)
18
Oscillator Capacitor
The PWM oscillator frequency can be set by an external capacitor. The internal oscillator uses a 28kΩ
resistor to charge / discharge the external capacitor to a trip voltage of 2/3 Vcc respectively 1/3 Vcc. It
can be overdriven using an external CMOS level square wave signal. Do not set the frequency higher
than 100kHz and do not leave the OSC terminal open! The two bridges are chopped with a phase shift
of 180 degrees at the positive and at the negative edge of the clock signal.
fOSC
≈
40µs
×
1
COSC
[nF]
fOSC: PWM oscillator frequency
COSC: Oscillator capacitor in nF
Table of oscillator frequencies
f_OSC typ.
16.7kHz
20.8kHz
25.0kHz
30.5kHz
36.8kHz
44.6kHz
C_OSC
1.5nF
1.2nF
1.0nF
820pF
680pF
560pF
Please remark, that an unnecessary high frequency leads to high switching losses in the power
transistors and in the motor. For most applications a chopper frequency slightly above audible range is
sufficient. When audible noise occurs in an application, especially with mixed decay continuously
enabled, the chopper frequency should be two times the audible range. For most applications we
recommend a frequency of 36.8kHz.
Pullup resistors on unused inputs
The digital inputs all have integrated pull-up resistors, except for the ENN input, which is in fact an
analog input. Thus, there are no external pull-up resistors required for unused digital inputs which are
meant to be positive.
Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG