Motorola Corporation

John M Hargedon

Randall T Wollschlager

Keith M Wellnitz

Jeffrey A Kanner

A half-bridge driver provides a current limit on the low-side driver (20) and a current limit on the high-side driver (16). The current limits are initially set equal. If the low-side driver current limits, then a modulation current from the low-side driver increases the high-side driver current limit threshold to maintain stable operation of the control circuits. In addition, the present invention provides dual conduction paths to charge the main conduction transistor of the low-side driver, while detecting current limit. When current limit is detected, the charging current to the main conduction transistor is switched to current limit mode.

Circuit and method of current limiting a half-bridge driver

A clamp circuit (10) for protecting a MOSFET (12) from destructive voltages and currents includes a clamping element (30), a current switch (27), a bond pad (23), a probe pad (25), and a resistor (21). When no external signal is applied to the probe pad (25), a FET (18) in the clamping element (30) is conductive. When the drain voltage of the MOSFET (12) rises above a clamping voltage of the clamping element (30), a current flows through the clamping element (30) and switches on the MOSFET (12). To ensure a safe operating area of the MOSFET (12), a voltage is applied to the probe pad (25) to turn off the FET (18), a breakdown voltage of the MOSFET (12) measured from the bond pad (23) is compared with the clamp voltage, and circuit die with the breakdown voltage less than the clamp voltage are discarded.

Clamp circuit and method for identifying a safe operating area

A clamp circuit (50) for protecting a MOSFET (52) from destructive voltages includes a clamping element (56), a Zener diode (64), two current mirrors (66 and 62), a current switch (58), a reference current source (68), and a voltage detector (72). When a drain voltage of the MOSFET (52) rises above a clamping voltage of the clamp circuit (50), a clamping current exceeding a current in the current switch (58) flows through the clamping element (56) and activates the MOSFET (52). During the activation, the two current mirrors (66 and 62) generate an output current exceeding a reference current in the reference current source (68) and raise a voltage at an input terminal of the voltage detector (72). The voltage detector (72) generates a signal indicating the activation of the clamp circuit (50), thereby indicating that the clamp circuit (50) and its inductive load (74) are intact.

Clamp circuit and method for detecting an activation of same

An actuator movement detector (10) indicates proper engagement of a solenoid (12). The current flowing through a field coil (16) is converted to a sense voltage that exponentially increases and then follows a dip before increases again to a steady state value greater than the first peak value. The exponentially increasing sense voltage is stored across a capacitor (24). Any AC variation about the stored sense voltage sets the output state of comparators (30, 32) and determines a first peak value of the sense voltage. After the first peak, a counter (44) must count to a predetermined value during the low peak before the sense voltage returns to its first peak value. If the counter reaches at least the predetermined count value before returning to its first peak value and count back down to zero before reaching steady state, then the solenoid is considered engaged.

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Chandler, AZ, United States of America

John M Hargedon