Transistor switch including independent control of turn-on and slew rate

摘要

The disclosed transistor switching methodology enables independent control of transistor turn-on delay and slew rate, including charging, during a pre-charge period, a transistor control input to a threshold voltage VT with a predetermined turn-on delay; and then charging, during a switch-on period, the transistor control input from VT to an operating point with a predetermined slew rate. This methodology is adaptable to load switching applications, for example, to control a high side/low side load switch such that, during the switch on period, the output voltage supplied to the load rises from zero volts to an operating load voltage with the predetermined slew rate. In one embodiment, I_delay and I_slew_rate currents are used to charge the transistor control input respectively during the pre-charge and switch-on periods. In another embodiment, the I-delay and I-slew rate currents are controlled by a replica switch with a control input coupled to the control input of a main switch, with the replica switch characterized by a threshold voltage substantially identical to the main switch threshold voltage VT.

主权项

1. A transistor switch circuit, comprising
a transistor switch characterized by a turn-on threshold voltage VT; and switch control circuitry coupled to a control input of the transistor, and configured to independently control turn-on delay and output voltage slew rate, including:
pre-charge circuitry including a source of I delay current operable during a pre-charge period initiated by a switch-on signal, to charge the transistor control input to VT with a predetermined turn-on delay;switch-on circuitry including a source of I slew rate current operable during a switch-on period, to charge the transistor control input from VT to an operating point with a predetermined slew rate; andcharge control circuitry including:
a replica switch with a control input coupled to the control input of the transistor switch, collectively the shared control inputs, the replica switch characterized by a threshold voltage substantially identical to the transistor switch threshold voltage VT; anda switch network controlled by the replica switch such that (a) during the pre-charge period, the replica switch is operable to connect the I delay current to charge the shared control inputs to VT such that the replica switch switches on to initiate the switch-on period, and (b) during the switch-on period, the replica switch is operable to connect the I slew rate current to charge the transistor switch control input to the operating point with the predetermined slew rate.