The UCD7242 is a complete power system ready to drive two independent buck power supplies. High side MOSFETs, low side MOSFETs, drivers, current sensing circuitry and necessary protection functions are all integrated into one monolithic solution to facilitate minimum size and maximum efficiency. Driver circuits provide high charge and discharge current for the high-side NMOS switch and the low-side NMOS synchronous rectifier in a synchronous buck circuit. The MOSFET gates are driven to +6.25 V by an internally regulated VGG supply. The internal VGG regulator can be disabled to permit the user to supply an independent gate drive voltage. This flexibility allows a wide power conversion input voltage range of 2.2V to 18V. Internal under voltage lockout (UVLO) logic ensures VGG is good before allowing chip operation.
The synchronous rectifier enable (SRE) pin controls whether or not the low-side MOSFET is turned on when the PWM signal is low. When SRE is high the part operates in continuous conduction mode for all loads. In this mode the drive logic block uses the PWM signal to control both the high-side and low-side gate drive signals. Dead time is also optimized to prevent cross conduction. When SRE is low, the part operates in discontinuous conduction mode at light loads. In this mode the low-side MOSFET is always held off.
On-board comparators monitor the current through the high side switch to safeguard the power stage from sudden high current loads. Blanking delay is set for the high side comparator to avoid false reports coincident with switching edge noise. In the event of an over-current fault, the high-side FET is turned off and the Fault Flag (FLT) is asserted to alert the controller.
MOSFET current is measured and monitored by a precision integrated current sense element. This method provides an accuracy of ±5% over most of the load range. The amplified signal is available for use by the controller on the IMON pin.
An on-chip temperature sense converts the die temperature to a voltage at the TMON pin for the controller’s use. If the die temperature exceeds 170°C, the temperature sensor initiates a thermal shutdown that halts output switching and sets the FLT flag. Normal operation resumes when the die temperature falls below the thermal hysteresis band.