The boost converter integrates Silent Switcher technology and input disconnect functionality, delivering outstanding performance and reliable protection.

Traditional synchronous boost converters offer virtually no protection against output short-circuit events. The topology of boost converters dictates that when the output is shorted to ground, a direct path from input to ground is formed, resulting in substantial short-circuit currents that may severely damage the device. In contrast, this single-chip synchronous boost converter incorporates short-circuit protection functionality. It monitors the input and disconnects it upon detection of a short circuit, thereby safeguarding the device from damage.

The LT8342 integrates a 40 V, 9 A power switch with a programmable output voltage up to 36 V. It also supports a wide input voltage range from 2.8 V to 40 V; for VIN ≥ VOUT conditions, it supports PassThru mode. In Burst Mode operation, the integrated circuit (IC) exhibits extremely low static current at the VIN pin. It can be programmed or synchronised to a maximum frequency of 3 MHz, thereby reducing the size of external components and the overall core solution. Employing the Silent Switcher architecture, the device achieves high efficiency while effectively minimising electromagnetic interference (EMI). It is housed in a compact 4 mm × 4 mm LQFN package.

High-performance 24 V, 3 A power supply

Figure 1 illustrates a 24 V boost application incorporating output short-circuit protection. When the input voltage exceeds 12 V, it can deliver a maximum load current of 3 A. With a 15 kΩ resistor placed on the RT pin, the switching frequency is set to 2 MHz.

Figure 1. 2 MHz, 24 V Boost Converter with Output Short-Circuit Protection

By configuring the SYNC/MODE pin, this boost converter can operate in either Burst Mode or Skip Mode, depending on application requirements. Burst Mode delivers higher efficiency under light load conditions, whilst Skip Mode reduces output ripple. Figure 2 illustrates the efficiency of this 24 V application in Burst Mode (SYNC/MODE = 0 V). Efficiency remains above 70% under light load conditions; when the input voltage is 20 V, efficiency peaks at over 95% at 3 A.

Figure 2. Relationship between efficiency and power loss versus current in burst mode (SYNC/MODE = 0 V)

Figure 3. Conducted EMI Performance (CISPR 25 Class 5 Peak)

Low IQ current

In burst mode operation, the LT8342 delivers a small single-pulse current to maintain the output voltage before entering a sleep cycle. During sleep, the VIN pin draws only 9 μA when short-circuit protection is disabled, or 28 μA when enabled. The smaller the load, the greater the proportion of time the device spends in sleep mode, thereby enhancing efficiency under light loads. Furthermore, the IC consumes merely 350 nA of input quiescent current when in shutdown mode.

CISPR 25 Category 5 Radiated Emissions Results

This IC offers an optional Spread Spectrum Frequency Modulation (SSFM) mode, which, combined with the Silent Switcher architecture, further reduces EMI emissions. When SSFM is enabled by configuring the SYNC/MODE pin, the internal oscillator frequency varies between its programmed value and a value approximately 13% higher. Conducted and radiated EMI results according to CISPR 25 Class 5 standards are shown in Figures 3 and 4 respectively. SSFM may also be activated in burst mode or pulse-skipping mode, thereby simultaneously achieving low EMI and high efficiency.

Figure 4. Radiated EMI Performance (CISPR 25 Class 5 Peak)

Short-circuit protection

This converter incorporates an output short-circuit protection mechanism to prevent damage during short-circuit events. An external sense resistor and N-channel FET (connected in series with the converter input) monitor the current and disconnect the input when necessary. When the current flowing through the sense resistor rises sufficiently to trigger the internal comparator's voltage threshold, the IC pulls the GATE pin to ground, thereby turning off the external FET and limiting the short-circuited inductor current. The waveforms in Figures 5 and 6 illustrate the typical response of the IC during an output short-circuit event.

Figure 5. Output Short-Circuit Protection

The internal hiccup timer counts for 40 milliseconds before re-engaging the external FET. Should the short circuit persist, the input will disconnect once more when the trigger current detection occurs.

Figure 6. Intermittent glitches during output short-circuit conditions

Pass-Through Mode

The LT8342 is ideally suited for automotive pre-boost applications where the boost converter's input voltage typically exceeds the regulated output voltage. When this occurs, the IC enters PassThru mode. The top integrated synchronous power switch maintains a 100% duty cycle on-state, whilst the bottom switch remains off-state, thereby creating a direct path from input to output. The device also enters a low quiescent current state: consuming 12 μA when short-circuit protection is disabled, and 26.5 μA when an external input disconnect FET is employed. Figure 7 illustrates a pre-boost application for automotive start-stop and cold-start scenarios, whilst Figure 8 demonstrates operation with PassThru mode activated.

Figure 7. 2 MHz pre-boost converter for automotive start-stop and cold-start applications, providing a 10 V output with short-circuit protection.

Figure 8. PassThru operating mode, VIN = 12 V, ILOAD = 1 A

The LT8342 integrates multiple features within a compact package, delivering low noise, low input current, high efficiency and circuit protection. With its wide input and output ranges, programmable switching frequency, low noise and PassThru mode, this device is ideally suited for general boost applications and automotive pre-boost applications. Burst mode operation and low input quiescent current enable it to achieve higher efficiency than typical boost converters under light load conditions.