Intersil has developed a synchronous step-down controller that uses a constant-on-time PWM (pulse width modulation) architecture with a programmable switching frequency of up to 600KHz. Intersil says the control feature handles wide input/output voltage ratios with ease and provides 100ns ‘instant-on’ response to load transients while maintaining efficiency and a constant switching frequency. Typical applications include DDR memory in desktops, notebooks and graphics cards, and other applications that require voltages down to 0.7V.
With up to 95% efficiency, Intersil’s ISL88550A integrates a synchronous buck PWM controller, a sourcing and sinking low drop-out regulator, and a 10mA reference output buffer.
The PWM controller generates VDDQ (voltage for double data rate memory), the LDO regulator generates VTT (termination voltage supply) and the reference output buffer generates VTTR (termination voltage reference).
The ISL88550A drives two external N-Channel MOSFETs to generate output voltages down to 0.7V from a 2V to 25V input with output currents up to 20A. The LDO can sink or source up to 2.5A. Both the LDO output and the 10mA reference buffer output can be designed to track the REFIN voltage through a built-in resistive divider. The device also offers programmable UVP/OVP and skip mode options suited to portable applications. Skip mode allows for improved efficiency at lighter loads.
The VTT and VTTR outputs of the ISL88550A track within 1% of VREFIN/2. The high bandwidth of this LDO regulator allows transient response without bulky capacitors, reducing system cost and size.