The ISL88550AEVAL1Z evaluation board is used to demonstrate the performance of the ISL88550A synchronous step-down controller with sourcing and sinking LDO regulator.
ISL88550A integrates a synchronous buck PWM controller to generate VDDQ, a sourcing and sinking LDO linear regulator to generate VTT, and a 10mA reference output buffer to generate VTTR. The buck controller 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 15A. The LDO can sink or source up to 1.5A continuous and 2.5A peak current with fast response. Both the LDO output and the 10mA reference buffer output can be made to track the REFIN voltage via a built-in resistive divider. These features make the ISL88550A ideally suited for DDR memory applications in desktops, notebooks and graphic cards.
The PWM controller in the ISL88550A uses constant-on-time PWM architecture with a programmable switching frequency of up to 600kHz. This control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining high efficiency and a relatively constant switching frequency. The ISL88550A offers full programmable UVP/OVP and skip mode options ideal in portable applications. Skip mode allows for improved efficiency at lighter loads.
The VTT and VTTR outputs track to within 1% of VREFIN/2. The high bandwidth of this LDO regulator allows excellent transient response without the need for bulk capacitors, thus reducing the cost and size.
- Constant-On PWM with 100ns load-step response
- Up to 95% efficiency
- Input voltage range (VIN): 2V to 25V
- Adjustable output: 1.8V/2.5V fixed or 0.7V to 3.5V
- Switching frequencies: 200kHz, 300kHz, 450kHz, 600kHz
- Programmable current limit with foldback capability
- 1.7ms digital soft-start and independent shutdown
- Overvoltage/Undervoltage protection option
- Power-good window comparator
- Fully integrated VTT and VTTR capability
- VTT has ±2.5A sourcing/sinking capability
- VTT and VTTR outputs track VREFIN/2
- VTT and VTTR within 1% of VREFIN/2
- All ceramic output capacitor designs
- 1.0V to 2.8V input REFIN range
- Analog soft-start option and independent shutdown
- Power-good window comparator
- DDR, DDR II and DDR III memory power supplies
- Desktop computers
- Notebooks and Desknotes
- Graphics cards
- Game consoles
- Networking and RAID
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