MAX1771 — High-Efficiency Step-Up DC-DC Controller

Overview

The MAX1771 (MAX1771CSA / MAX1771CPA) is a high-efficiency current-mode step-up (boost) DC-DC controller IC manufactured by Analog Devices (Maxim Integrated). Designed to drive an external N-channel power MOSFET, it is legendary among electronics makers as the gold-standard controller for building high-voltage ( $170\text{V} \dots 200\text{V}$ DC) Nixie tube power supplies from low-voltage $9\text{V} \dots 12\text{V}$ DC wall adapters.

Operating across an input supply voltage range of 2.0V to 16.5V DC, the MAX1771 utilizes a BiCMOS pulse-frequency modulation (PFM) control scheme to achieve up to 90% efficiency while drawing an ultra-low quiescent current of just $110\ \mu\text{A}$ .

Quick reference


Input Supply Voltage (`V+`)	2.0 V to 16.5 V DC
Output Voltage Range	Adjustable up to $200\text{ V}+$ DC (Determined by external MOSFET rating & feedback divider)
Control Scheme	Current-Limited PFM (Pulse-Frequency Modulation)
Max Switching Frequency	Up to $300\text{ kHz}$
Quiescent Current	$110\ \mu\text{A}$ typical ( $11\ \mu\text{A}$ in shutdown mode)
Reference Voltage (`REF`)	$1.5\text{ V}$ precision output reference pin
Package	8-pin SOIC / 8-pin DIP

Pinout (DIP-8 / SOIC-8 Package)

text

             ┌───┴───┐
        EXT 1│ 1   8 │ CS (Current Sense Input)
         V+ 2│       │ 7 GND (Power Ground)
         FB 3│MAX1771│ 6 AGND (Analog Ground)
       SHDN 4│       │ 5 REF (1.5V Reference Out)
             └───────┘

Pin	Name	Type	Description
1	`EXT`	Output	External N-Channel MOSFET Gate Drive Output
2	`V+`	Power	Positive Supply Voltage Input (+2.0V to +16.5V DC)
3	`FB`	Input	Feedback Voltage Sense Input ( $1.5\text{V}$ reference to AGND)
4	`SHDN`	Input	Active-HIGH Shutdown Input (High = Shutdown; Low = Normal Operation)
5	`REF`	Output	Internal 1.5V Reference Output (Decouple with 0.1µF capacitor to AGND)
6	`AGND`	Power	Analog Signal Ground (Connect to GND near chip)
7	`GND`	Power	Heavy Current Power Ground
8	`CS`	Input	Current Sense Input (Connect to sense resistor $R_{SENSE}$ in series with N-FET source)

High-Voltage Nixie Tube Boost Supply Circuit (12V to 180V DC)

text

                       ┌───[ Fast High-Voltage Inductor 220µH ]───┬─── High-Voltage Output (+180V DC)
                       │                                          │
  +12V DC Supply ──────┴───────────┐                       [UF4007 Ultra-Fast Diode]
                                   │                              │
                           [Pin 2: V+]                            ├─── [Pin 1: EXT] ─── Gate N-FET (IRF640 / IRF840)
                               MAX1771                            │
                           [Pin 3: FB] ◄───[Feedback Divider]─────┤
                                                                  └─── [Pin 8: CS] ─── R_SENSE (0.05Ω) ─── GND

High Voltage Safety Warning

Caution

High Voltage Hazard! Nixie power supply circuits built with the MAX1771 generate $180\text{V} \dots 200\text{V}$ DC. Though non-lethal at low currents, contact causes painful electrical shocks and burns. Always discharge output capacitors before handling.

Common mistakes

Using a standard slow rectifier diode (like 1N4007): Standard 50Hz rectifiers cannot turn off fast enough at 300 kHz, causing thermal breakdown. Always use an ultra-fast recovery diode (such as the UF4007 or MUR160).
Poor PCB ground layout: High peak switching currents ( $> 3\text{A}$ ) through the MOSFET source resistor will corrupt the analog feedback input (FB). Keep power ground (GND) separate from analog ground (AGND) until a single star point near Pin 6.

Notes

MAX1771 vs MC34063: MAX1771 drives external high-voltage MOSFETs at up to 90% efficiency; MC34063 uses internal switches restricted to lower efficiency and lower voltages ( $40\text{V}$ ).