Reference Design for an Auxiliary Power Supply for an LCD TV or Set-Top Box Using the MAX15026

Abstract: This application note describes a reference design for building an auxiliary power supply for an LCD TV or set-top box using the MAX15026 low-cost, high-efficiency synchronous step-down converter . The reference design generates a 5V, 5A output from a 6.5V to 24V input voltage range.

The following lists the key specifications of the reference design, a detailed circuit schematic (Figure 1), and the required bill of materials (Table 1).

Specification

Input voltage range: 6.5V to 24V

Output voltage: 5V

Output current: 5A

Output voltage ripple (peak to peak): 50mV

Converter Switching Frequency: 300kHz

Overcurrent protection limit: 6A

Efficiency: > 90% (standard working mode)

Figure 1. Circuit diagram of the MAX15026 synchronous-rectifier step-down converter at 300kHz switching frequency.

Performance Data

Figure 2. Regulated output, input voltage, and switch node voltage for VIN = 24V, VOUT = 5V.

Ch1: VOUT; Ch2: VIN; Ch3: LX node voltage

Figure 3. Enable, soft-start, soft-stop, and PGOOD timing waveforms.

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Ch1: Enable; Ch2: VOUT; Ch3: PGOOD

Figure 4. Output and input ripple at VIN = 24V, VOUT = 5V, and IOUT = 5A.

Ch1: output voltage ripple; Ch2: input voltage ripple

Figure 5. Converter transient response to a 2A load current step change.

Ch1: output voltage; Ch2: load step change (1A/div)

Test conditions

V = 12V, V = 5V

Load current step change: 1A to 3A

Load current slew rate: 2A/?s

Figure 6. Hiccup mode overcurrent protection during output short circuit.

CH1: output voltage; CH2: gate pulse

Figure 7. Efficiency vs. load current curve