ZHCSHF4J May 2004 – January 2018 TPS51116
PRODUCTION DATA.
The main control loop of the SMPS is designed as an adaptive on-time pulse width modulation (PWM) controller. It supports two control schemes which are a current mode and a proprietary D-CAP™ mode. D-CAP™ mode uses internal compensation circuit and is suitable for low external component count configuration with an appropriate amount of ESR at the output capacitor(s). Current mode control has more flexibility, using external compensation network, and can be used to achieve stable operation with very low ESR capacitor(s) such as ceramic or specialty polymer capacitors.
These control modes are selected by the COMP terminal connection. If the COMP pin is connected to V5IN, TPS51116 works in the D-CAP™ mode, otherwise it works in the current mode. VDDQ output voltage is monitored at a feedback point voltage. If VDDQSET is connected to V5IN or GND, this feedback point is the output of the internal resistor divider inside VDDQSNS pin. If an external resistor divider is connected to VDDQSET pin, VDDQSET pin itself becomes the feedback point (see VDDQ Output Voltage Selection section).
At the beginning of each cycle, the synchronous high-side MOSFET is turned on, or becomes ON state. This MOSFET is turned off, or becomes OFF state, after internal one shot timer expires. This one shot is determined by VIN and VOUT to keep frequency fairly constant over input voltage range, hence it is called adaptive on-time control (see PWM Frequency and Adaptive On-Time Control section). The MOSFET is turned on again when feedback information indicates insufficient output voltage and inductor current information indicates below the overcurrent limit. Repeating operation in this manner, the controller regulates the output voltage. The synchronous low-side or the rectifying MOSFET is turned on each OFF state to keep the conduction loss minimum. The rectifying MOSFET is turned off when inductor current information detects zero level. This enables seamless transition to the reduced frequency operation at light load condition so that high efficiency is kept over broad range of load current.
In the current mode control scheme, the transconductance amplifier generates a target current level corresponding to the voltage difference between the feedback point and the internal 750 mV reference. During the OFF state, the PWM comparator monitors the inductor current signal as well as this target current level, and when the inductor current signal comes lower than the target current level, the comparator provides SET signal to initiate the next ON state. The voltage feedback gain is adjustable outside the controller device to support various types of output MOSFETs and capacitors. In D-CAP mode, the transconductance amplifier is disabled and the PWM comparator compares the feedback point voltage and the internal 750-mV reference during the OFF state. When the feedback point comes lower than the reference voltage, the comparator provides SET signal to initiate the next ON state.