说明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.
- 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
|Part Number||Primary Topology||DC-DC/Power Features||VIN|
技术资料设计指南 4992 Reduce the Chances of Human Error: Part 1, Power and Ground
应用笔记 3672 Noise Reduction for the MAX1864 Auxiliary Regulator
应用笔记 3654 Current Limiting for the MAX1864 Auxiliary Regulator
应用笔记 3626 Adding a Watchdog to a Dual-Output Power Supply
应用笔记 1857 DDR Memory-Termination Supply
应用笔记 1843 Noise Reduction For ADSL Modem Power
应用笔记 906 The MAX1864 Generates 1.2V or Lower Output Voltage
应用笔记 905 Adding POR Function to the MAX1864 Generating Two Outputs
应用笔记 821 Compensation Calculator for the MAX1864/MAX1865 xDSL Cable-Modem Power Supplies
设计指南 735 Layout Considerations for Non-Isolated DC-DC Converters