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Dynamic step-down dc-dc converters

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MAXIM Integrated Products, represented by Arrow Electronics , has introduced the MAX8500/MAX8503/MAX8504, the company's second generation of step-down dc-dc converters designed specifically for the linear power amplifier (PA) used in 2.5G and 3G cellular phones.

The high-speed MAX8500 and MAX8503 can vary their output voltage from 0.4V to 3.4V in less than 30 microseconds, thereby adjusting the power applied to the PA.

This tracking of the transmit power improves efficiency up to 47 per cent at +10dBm and is dynamically controlled from the phone's baseband processor.

The MAX8504 is programmed for fixed 1.25V to 2.5V output with external resistors.

The MAX8500/MAX8503/MAX8504 are pulse-width modulated (PWM) converters with a 1MHz switching frequency and can deliver up to 600mA.They have an input range of 2.6V to 5.5V for use with a single lithium-ion (Li+) battery.

They integrate a bypass FET (0.25 ohm typ), allowing operation directly from the battery at heavy loads.

For light loads, the MAX8500 and MAX8503 utilise an LDO regulator to bypass the external inductor to eliminate switching losses.

The MAX8500/MAX8503/MAX8504 can operate up to 100 per cent duty cycle.

Dropout is only 150mV at 600mA load to give longer useful operating life to the battery. Quiescent supply current is only 280 microamps and drops to 0.1 microamp in logic-controlled shutdown.

The MAX8500/MAX8503/MAX8504 come in a 0.8mm high 12-pin thin QFN package (4mm x 4mm). The ICs are screened for the extended industrial temperature range (-40°C to +85°C).

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