2.1 Buck Channels and Related External Components

The MCP16503 buck channels are based on peak-current-mode control architecture and have internal frequency compensation for the voltage regulation loop. The slope compensation is optimized for inductors in the 1.5μH to 2.2μH range. A minimum output capacitor of 22μF is required for stable operation. Output capacitance can be increased if necessary, however the maximum output capacitance value should be limited to avoid engaging hiccup-mode overcurrent protection during the initial soft-start ramp and during DVS operation. Further details are given in section Maximum Simultaneous Capacitive and DC Loading in Soft-Start and DVS

The buck channels of the MCP16503 also feature a negative inductor current limit protection when operating in forced PWM mode. This prevents dangerous current levels in the power train. If the inductor current reaches the low-side negative peak current limit (I_{LIM_NEGx} ) while the low-side MOSFET is conducting, the low-side MOSFET is turned off and the inductor current is pushed to the input voltage, either through the body diode of the high-side MOSFET (if OFF) or its channel (when turned ON by the control loop). Since this feature is only intended to protect the device in some particular transient conditions (such as a large decrease of the output voltage setting associated with an extremely large capacitive load), it is only reported through I²C, but it does not cause the assertion of the nRSTO (RESET) signal.

This protection should never be exercised continuously and/or without a very large bulk capacitor, because it may quickly destroy the device.

When this protection is engaged, energy is pumped back from the output into the input voltage. If the input supply has no sinking capability and/or the input bulk decoupling cap is not large enough, the input voltage will rise to the point where the device is permanently damaged.

LDOs are protected against short-circuits by a linear constant-voltage, constant-current (i.e., brick-wall) output characteristic. The output current under short-circuit conditions is not intermittent. Therefore, the internal power dissipation in the MCP16503 can reach high levels under LDO short-circuit conditions. The current limit condition of each LDO is also reported through I²C. The intervention of the LDO current limit protection does not cause the assertion of the nRSTO (RESET) signal.

The recommended input decoupling capacitance on each buck channel is 4.7μF.

The buck channels can operate either in forced PWM mode (continuous inductor current mode), where the inductor current is allowed to go negative, or in automatic PFM mode, where the inductor current is not allowed to go negative through zero-current detection (ZCD) and diode emulation of the low-side MOSFET.

The switching frequency in forced PWM mode is nominally 2MHz and can be displaced through I²C by ±16.5% to prevent interference with other sensitive system blocks.

Recommended part numbers are given in section Recommended External Components.