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Schematic of nSLEEP and nFAULT pins on DRV8824/DRV8825/DRV8834 carriers.
The DRV8825 also features a FAULT output that drives low whenever the H-bridge FETs
are disabled as the result of over-current protection or thermal shutdown. The carrier
board connects this pin to the SLEEP pin through a 10k resistor that acts as
a FAULT pull-up whenever SLEEP is externally held high, so no external pull-up is
necessary on the FAULT pin. Note that the carrier includes a 1.5k protection resistor in
series with the FAULT pin that makes it is safe to connect this pin directly to a logic
voltage supply, as might happen if you use this board in a system designed for the pin-
compatible
A4988
carrier
.
In
such
a
system,
the
10k
resistor
between SLEEP and FAULT would then act as a pull-up for SLEEP, making the DRV8825
carrier more of a direct replacement for the A4988 in such systems (the A4988 has an
internal pull-up on its SLEEP pin). To keep faults from pulling down the SLEEP pin, any
external pull-up resistor you add to the SLEEP pin input should not exceed 4.7k.
CURRENT LIMITING
To achieve high step rates, the motor supply is typically much higher than would be
permissible without active current limiting. For instance, a typical stepper motor might
have a maximum current rating of 1 A with a 5Ω coil resistance, which would indicate a
maximum motor supply of 5 V. Using such a motor with 12 V would allow higher step
