Analog Devices MAX1856 Product Info

• 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

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.

Applications

• Cable and DSL Modems
• CO DSL Line Driver Supplies
• FTTH
• Industrial Power Supplies
• LMDS/MMDS
• MEMS Bias Supplies
• Routers/Switches
• Set-Top Boxes