TMC239 / TMC239A DATA SHEET (V2.11 / 2009-Jul-30)

21

Copyright © 2005, TRINAMIC Motion Control GmbH & Co KG

Oscillator Capacitor

The PWM oscillator frequency can be set by an external capacitor. The internal oscillator uses a 28k

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.

[nF]

C

s

40

1

f

OSC

OSC

PWM oscillator frequency

Oscillator capacitor in nF

Table of oscillator frequencies

16.7kHz

1.5nF

20.8kHz

1.2nF

25.0kHz

1.0nF

30.5kHz

820pF

36.8kHz

680pF

44.6kHz

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.

Pull-up 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.

Power supply sequencing considerations

Upon power up, the driver initializes and switches off the bridge power transistors. However, in order

for the internal startup logic to work properly, the Vcc supply voltage has to be at least 1.0V,

respectively, the Vs supply voltage has to be at least 5.0V. When Vs goes up with Vcc at 0V, a medium

current temporary cross conduction of the power stage can result at supply voltages between 2.4V and

4.8V. In this voltage range, the upper transistors conduct, while the gates of the lower transistors are

floating. While this typically does no harm to the driver, it may hinder the power supply from coming up

properly, depending on the power supply start up behavior.

There are two possibilities to prevent this from occurring:

Add resistors from the LA and LB outputs to GND in the range of 1M

keeping the low side N-

channel MOSFETs gates at GND.

Alternatively, either use a dual voltage power supply, or use a local regulator, generating the 5V or

3.3V Vcc voltage.

Please pay attention to the local regulator start up voltage: Some newer switching regulators do not

start, before the input voltage has reached 5V. Therefore it is recommended to use a standard

linear regulator like 7805 or LM317 series or a low drop regulator or a switching regulator like the

LM2595, starting at relatively low input voltages.