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PWM controllers eliminate the need for current-sensing resistor

24th November 2006

ES Admin

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Intersil’s ISL6545 and ISL6545A single-output PWM (pulse width modulation) controllers allow a lower BOM cost by integrating the boot diode, the overcurrent protection, and the MOSFET drivers onto a single chip, reducing the number of external components and saving on board space. The devices’ overcurrent function protects the controllers from a shorted output by using the lower MOSFET’s on-resistance, rDS(ON), to monitor the current, enhancing the efficiency of the controllers and reducing cost by eliminating the current-sensing resistor.

The wide input range (1.0V to 12V) of the devices provides design flexibility, while the wide voltage output range (0.6V to VIN) allows them to be used in a broad range of applications. The ISL6545 and ISL6545A make it simple to implement a complete control and protection scheme for a DC/DC step-down converter driving inexpensive N-channel MOSFETs in a synchronous buck topology. A fixed frequency oscillator (300kHz for ISL6545; 600KHz for ISL6545A) reduces design complexity while reducing typical application cost and increasing efficiency, allowing the devices to be used in small form factor applications.

The devices provide a single feedback loop and voltage-mode control with fast transient response. The output voltage can be precisely regulated to as low as 0.6V with a maximum tolerance of +1.0% over temperature and line voltage variations.

The error amplifier of the ISL6545 and ISL6545A feature a 20MHz gain bandwidth product and 9V/µs slew rate that enables high converter bandwidth for fast transient performance. The resulting PWM duty cycles range from 0% to 100%.

A fixed internal soft start, capable into a pre-biased load allows a controlled monotonic soft start. The devices operate from +5V or +12V supply voltage (for bias), the integrated gate drivers use VCC (5V - 12V), and they feature a 0.6V internal reference; ±1.0% tolerance.

Other key features of the ISL6545 and ISL6545A include a lossless, programmable overcurrent protection, an enable/shutdown function on COMP/SD pin, output current sourcing and sinking, and they drive N-Channel MOSFETs.

The vast range of target applications for the devices include power supplies for microprocessors or peripherals, PCs, embedded controllers, memory supplies, DSP and core communications processor supplies, subsystem power supplies, PCI, AGP; graphics cards; digital TV, SSTL-2 and DDR/DDR2/DDR3 SDRAM bus termination supply, cable modems, set top boxes, and DSL modems, Industrial power supplies; general purpose supplies, 5V or 12V-input DC/DC regulators, and low-voltage distributed power supplies.

The ISL6545 and ISL6545A are available now in an 8-lead SOIC package or a 10-lead, 3mm x 3mm QFN package. Pb-free plus anneal is also available (RoHS compliant). The small form factor ISL6545 and ISL6545A provide maximum performance and reliability for today’s power applications.