Features and Benefits

  • Low-Cost, Off-the-Shelf Transformer
  • 3V to 28V Input Range
  • Low Audio-Band Noise on Talk Battery
  • Effectively Handles Ring Trip Transients
  • Powers 2-, 4-, or 12-Line Equipment
  • High Efficiency Extends Battery Life During Life-Line Support Conditions
  • Adjustable 100kHz to 500kHz Switching Frequency
  • Clock Synchronization
  • Internal Soft-Start
  • Current-Mode PWM and Idle Mode™ Control Scheme
  • Logic-Level Shutdown
  • 10-Pin µMAX Package

Product Details

The MAX1856 offers a low-cost solution for generating a SLIC (ringer and off-hook) power supply. Using standard off-the-shelf transformers from multiple vendors, the MAX1856 generates various output voltages: -24V and -72V (dual output) for both ringer and off-hook supplies for voice-enabled broadband consumer premises equipment (CPE), -48V for IP phones and routers, -5V and -15V (single or dual output) for DSL CO line drivers, or negative voltages as high as -185V for MEMS bias supplies. The output voltages are adjusted with an external voltage divider.

Due to its wide operating voltage range, the MAX1856 operates from a low-cost, unregulated DC power supply for cost-sensitive applications like xDSL, cable modems, set-top boxes, LMDS, MMDS, WLL, and FTTH CPE. The MAX1856 provides low audio-band noise for talk battery and a sturdy output capable of handling the ring trip conditions for ring battery.

The operating frequency can be set between 100kHz and 500kHz with an external resistor in free-running mode. For noise-sensitive applications, the MAX1856's operating frequency can be synchronized to an external clock over its operating frequency range.

The flyback topology allows operation close to 50% duty cycle, offering high transformer utilization, low ripple current, and less stress on input and output capacitors. Internal soft-start minimizes startup stress on the input capacitor, without any external components.

The MAX1856's current-mode control scheme does not require external loop compensation. The low-side current-sense resistor provides accurate current-mode control and overcurrent protection.


  • Cable and DSL Modems
  • CO DSL Line Driver Supplies
  • FTTH
  • Industrial Power Supplies
  • MEMS Bias Supplies
  • Routers/Switches
  • Set-Top Boxes
  • VoIP Ringer and Off-Hook Voltage Generators
  • Wireless Local Loop (WLL)

Product Lifecycle icon-recommended Production

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Evaluation Kits (1)

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