MAX1865:xDSL/Cable Modem Triple/Quintuple Output Power Supplies

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.

Key Features
  • 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
MAX1864, MAX1865: Typical Operating Circuit
MAX1864, MAX1865: Typical Operating Circuit
  • Set-Top Boxes
  • Wireless Local Loop (WLL)
  • xDSL, Cable, and ISDN Modems
titleDownload file
MAX1864-MAX1865 Data SheetMAX1864-MAX1865.pdf
Part NumberPrimary TopologyDC-DC/Power FeaturesVIN
Oper. Freq.
Inverting OutputsPackage/PinsBudgetary
minmaxminmaxSee Notes
MAX1864Step-DownCurrent Limit
Fixed Freq./PWM
Soft Start
4.5281.25222.52.5200-QSOP/16$2.46 @1k
MAX18651QSOP/20$2.95 @1k
Design kits & evaluation modules
Ordering Information
Part NumberStatusRecommended ReplacementPackageTempRoHS
MAX1865TEEPNo Longer AvailableMAX1865TEEP+QSOP,;20 pin;54.2 mm²-40°C to +85°CNo
MAX1865TEEP+ActiveQSOP,;20 pin;54.2 mm²-40°C to +85°CLead Free
MAX1865TEEP+TActiveQSOP,;20 pin;54.2 mm²-40°C to +85°CLead Free
MAX1865TEEP-TNo Longer AvailableMAX1865TEEP+TQSOP;20 pin-40°C to +85°CSee data sheet
MAX1865UEEPNo Longer AvailableQSOP,;20 pin;54.2 mm²-40°C to +85°CNo
MAX1865UEEP-TNo Longer AvailableQSOP;20 pin-40°C to +85°CSee data sheet
MAX1864-MAX1865.pdf MAX1865
Reduce the Chances of Human Error: Part 1, Power and Ground MAX5481
Noise Reduction for the MAX1864 Auxiliary Regulator MAX1865
Current Limiting for the MAX1864 Auxiliary Regulator MAX1865
Compensation Calculator for the MAX1864/MAX1865 xDSL Cable-Modem Power Supplies MAX1865
Layout Considerations for Non-Isolated DC-DC Converters MAX1865
典型工作电路 MAX1865