Features and Benefits
- 4.5V to 28V Input Voltage Range
- Master DC-DC Step-Down Converter
- Preset 3.3V or Adjustable (1.236V to 0.8 x VIN) Output Voltage
- Fixed-Frequency (100kHz/200kHz) PWM Controller
- No Current-Sense Resistor
- Adjustable Current Limit
- 95% Efficient
- Two (MAX1864)/Four (MAX1865) Analog Gain Blocks
- Positive Analog Blocks Drive Low-Cost PNP Pass Transistors to Build Positive Linear Regulators
- Negative Analog Block (MAX1865) Drives a Low-Cost NPN Pass Transistor to Build a Negative Linear Regulator
- Power-Good Indicator
- Soft-Start Ramp for All Positive Regulators
The MAX1864/MAX1865 power-supply controllers are designed to address cost-conscious applications such as cable modem Consumer Premise Equipment (CPE), xDSL CPE, and set-top boxes. Operating off a low-cost, unregulated DC supply (such as a wall adapter output), the MAX1864 generates three positive outputs, and the MAX1865 generates four positive outputs and one negative output to provide a cost-effective system power supply.
The MAX1864 includes a current-mode synchronous step-down controller and two positive regulator gain blocks. The MAX1865 has one additional positive gain block and one negative regulator gain block. The main synchronous step-down controller generates a high-current output that is preset to 3.3V or adjustable from 1.236V to 0.8 x VIN with an external resistive-divider. The 100kHz/200kHz operating frequency allows the use of low-cost aluminum-electrolytic capacitors and low-cost power magnetics. Additionally, the MAX1864/MAX1865 step-down controllers sense the voltage across the low-side MOSFET's on-resistance to efficiently provide the current-limit signal, eliminating the need for costly current-sense resistors.
The MAX1864/MAX1865 generate additional supply rails at low cost. The positive regulator gain blocks use an external PNP pass transistor to generate low-voltage rails directly from the main step-down converter (such as 2.5V or 1.8V from the main 3.3V output) or higher voltages using coupled windings from the step-down converter (such as 5V, 12V, or 15V). The MAX1865's negative gain block uses an external NPN pass transistor in conjunction with a coupled winding to generate -5V, -12V, or -15V.
All output voltages are externally adjustable, providing maximum flexibility. Additionally, the MAX1864/MAX1865 feature soft-start for the step-down converter and all the positive linear regulators, and have a power-good output that monitors all of the output voltages.
- Set-Top Boxes
- Wireless Local Loop (WLL)
- xDSL, Cable, and ISDN Modems
Product Lifecycle 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.
Documentation & Resources
MAX1864 Reliability Data1/12/202371K
Adding a Watchdog to a Dual-Output Power Supply9/25/2005
DDR Memory-Termination Supply1/17/2003
The MAX1864 Generates 1.2V or Lower Output Voltage12/27/2001
Reduce the Chances of Human Error: Part 1, Power and Ground3/8/2011
Noise Reduction for the MAX1864 Auxiliary Regulator12/22/2005
Current Limiting for the MAX1864 Auxiliary Regulator11/16/2005
Noise Reduction For ADSL Modem Power12/29/2002
Adding POR Function to the MAX1864 Generating Two Outputs7/2/2002
Layout Considerations for Non-Isolated DC-DC Converters11/29/2001
Compensation Calculator for the MAX1864/MAX1865 xDSL Cable-Modem Power Supplies10/9/2001
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
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