BOOTSTRAPPED CHARGE PUMP CIRCUIT
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Feb-01
Charge pumps are used to provide a voltage higher than battery voltage to the gate of an N-channel MOSFET in automotive high-side-drive applications. A limitation of this method, especially if the charge pump uses a small IC capacitor, is slow turn-on of the FET-the gate charge of the FET is so large and the current sourcing capability of the charge pump so limited that it takes too long to develop sufficient gate voltage to turn the FET completely 'on? This problem prevents switching a large FET using an IC based charge pump (such as might be used in an automotive Solid State Relay) at speeds approaching 2OkHz. Boot-strap circuits are used to turn a FET quickly 'on: but they cannot be used to hold a FET 'on' for any length of time, due to non-zero gate leakage currents ofreal-world FETs.