Low-Noise, 14V Input, 1A, PWM Step-Down Converters

 

Part Number	Replacement	Explanation

Description

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The MAX1684/MAX1685 are high-efficiency, internal-switch, pulse-width modulation (PWM) step-down switching regulators intended to power cellular phones, communicating PDAs, and handy-terminals. These devices deliver a guaranteed 1A output current from two lithium-ion (Li+) batteries. Their wide-input voltage range of 2.7V to 14V gives design flexibility and allows batteries to charge from a wall cube, since the ICs operate at the higher voltages that occur when the battery is removed. The output voltage is preset to 3.3V or can be externally adjusted from 1.25V to V_IN.

The low on-resistance power switch and built-in synchronous rectifier provide high efficiencies of up to 96%. There are four modes of operation: fixed-frequency, normal, low-power, and shutdown. The fixed-frequency PWM mode of operation offers excellent noise characteristics. The normal mode maintains high efficiency at all loads. The low-power mode is used to conserve power in standby or when full load is not required. The shutdown mode is used to power down the device for minimal current draw.

The MAX1684 runs at 300kHz for applications that require highest efficiency. The MAX1685 runs at 600kHz to allow the use of smaller external components. These devices can also be synchronized to an external clock. Other features include a 100% duty cycle for low-dropout applications, an auxiliary 3V/5mA output, and a 1% accurate reference.

Both devices are available in a space-saving 16-QSOP package. An evaluation kit is also available to help speed designs. For a similar device in a 10-pin µMAX® package with lower input voltage requirements (5.5V max), refer to the MAX1692 data sheet.

MAX1684, MAX1685: Typical Operating Circuit Enlarge+

Key Features

• Up to 96% Efficiency
• 1A Guaranteed Output Current
• 100% Duty Cycle in Dropout
• 2.7V to 14V Input Range (15V Absolute Max)
• ±1% Accurate Reference Output
• 0.24Ω P-Channel On-Resistance
• Synchronizable Switching Frequency
• Fixed-Frequency PWM Operation
  • 300kHz (MAX1684)
  • 600kHz (MAX1685)
• 150µA Normal-Mode Quiescent Current
• 25µA Low-Power Mode Quiescent Current
• 2µA Shutdown Current
• Dual Mode™ Fixed 3.3V (±1%) Output or Adjustable Output (1.25V to V_IN)
• Small 16-QSOP Package
• Auxiliary Output (CVL): 3V/5mA

Applications/Uses

• Cell Phones
• Computer Peripherals
• PDAs and Handy-Terminals
• Personal Communicators
• Two-Way Radios and Walkie-Talkies