Texas Instruments Incorporated
Bus driver with rise/fall time control

Abstract:

A driver includes an open drain output transistor, a capacitor, a first current source, and first and second transistors. Upon assertion of a transmit signal to turn on the first transistor, a controller asserts a second control signal to turn on the second transistor responsive to a voltage of the capacitor being less than a threshold voltage of the open drain output transistor to thereby increase the control terminal voltage for the open drain output transistor at a first time rate. The controller deasserts the second control signal to turn off the second transistor responsive to the capacitor voltage exceeding the threshold voltage. Responsive to the capacitor's voltage exceeding the threshold, the first current source charges the capacitor to further increase the control terminal voltage at a second time rate that is smaller than the first time rate.