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Robust operation in adverse industrial environments

Applications

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PLCs

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Industrial process control and sensors

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Telecom and datacom power supplies

Details

Introduction

The MAXREFDES116# reference design (Figure 1) demonstrates the application of the MAX17599 low IQ,

wide-input range, active-clamp current-mode PWM controller. The MAX17599 contains all the control circuitry

required for the design of wide-input isolated forward-converter industrial power supplies. The reference design

operates over a 17V to 36V input-voltage range, and provides up to 8A at 5V output. The reference design

features the active-clamp transformer reset topology for forward converters. This reset topology has several

advantages including reduced voltage stress on the switches, transformer size reduction due to larger

allowable flux swing, and improved efficiency due to elimination of dissipative snubber circuitry. These features

result in a compact and cost-effective isolated power supply. The design is set to switch at 350kHz. For EMI-

sensitive applications, the user can program the frequency-dithering scheme, enabling low-EMI spread-

spectrum operation. Pins are 15.24mm (0.6in) from power to ground, and 50.8mm (2in) from the input side to

the output side.

The input-undervoltage lockout (EN/UVLO) is provided for programming the input-supply start voltage (set to

16.5V in the design) and to ensure proper operation during brownout conditions. The EN/UVLO input is also

used to turn on/off the IC. The overvoltage-input (OVI) protection scheme is provided to make sure that the

controller shuts down when the input supply exceeds its maximum allowed value (set to 37.0V in the design).

To control inrush current, the device incorporates a soft-start (SS) pin to set the soft-start time for the

regulator. Power dissipation under fault conditions is minimized by hiccup overcurrent protection

(hiccup mode). The soft-stop feature provides safe discharging of the clamp capacitor when the

device is turned off, and allows the controller to restart in a well-controlled manner.

Additionally, the negative current limit is provided in the current-sense circuitry, helping limit clamp-

switch current under dynamic operating conditions. An overtemperature fault triggers thermal

shutdown for reliable protection of the device.

The reference design delivers a peak efficiency of 91.5% with the supplied components when the

input is 24V. This general-purpose power solution can be used in many different types of power

applications, such as programmable logic controllers (PLC), industrial process control, industrial

sensors, telecom/datacom power supplies, isolated battery chargers, servers, and embedded

computing.