This article presents a small, powerful, low-noise monolithic synchronous boost converter. It also explores several features that enhance the performance of this IC and allow for customization to meet the needs of a variety of applications.

■ Monolithic synchronous boost converter with short-circuit protection

A typical boost converter provides little or no protection in the event of a short circuit at the output. Due to the inherent topology of the boost converter, a short to ground at the output creates a direct path from the input to ground, which can result in excessive current flow and damage to the device.

In contrast, this monolithic synchronous boost converter features short-circuit protection that monitors current and shuts down the input in the event of a short circuit, protecting the device from potential damage.

The LT8342 has an integrated 40V, 9A power switch and can produce an output voltage up to 36V. It also supports a wide input voltage range of 2.8V to 40V and includes PassThru™ mode operation for VIN ≥ VOUT. The IC features low VIN pin quiescent current in Burst Mode® operation and can be clocked up to 3MHz, either internally or with an external clock signal, reducing the total component area. Additionally, the device uses the Silent Switcher® architecture to deliver high efficiency while minimizing electromagnetic interference (EMI) emissions and is available in a small 4 mm × 4 mm LQFN package.

■ High-performance 24V, 3A power supply

Figure 1 shows a 24 V boost application with output short-circuit protection implemented. This application can supply up to 3 A of load current when the input voltage is 12 V or higher, and the switching frequency is set to 2 MHz by connecting a 15 kΩ resistor between the RT pin and ground.


By setting the SYNC/MODE pin, this boost converter can operate in either Burst Mode or Pulse-skipping mode, depending on the application's needs. Burst mode provides higher efficiency at light load conditions, while pulse-skipping mode reduces output ripple. Figure 2 shows the efficiency and power loss as a function of input voltage when operating in Burst Mode (SYNC/MODE = 0 V) in an application with a 24 V output voltage. It provides over 70% efficiency even under light load conditions, and can supply 24V/3A output with 95% efficiency when supplied with 20V input voltage.



■ Low IQ current

When operating in burst mode, the LT8342 supplies a small single current pulse to maintain the output voltage and then enters a sleep period. During this sleep period, the current supplied to the VIN pin is 9 μA when short-circuit protection is not enabled, and 28 μA when short-circuit protection is enabled. As the load becomes lighter, the device stays in sleep mode longer, improving efficiency. Additionally, the IC consumes only 350nA of input standby current when in shutdown mode.

■ CISPR 25 Class 5 Radiation Results4

The LT8342 offers an additional feature, spread spectrum frequency modulation (SSFM), along with the Silent Switcher architecture to further minimize EMI emissions. By enabling SSFM by setting the SYNC/MODE pin, the internal oscillator frequency varies between the set value and a value approximately 13% higher. The conducted and radiated EMI results, in accordance with the CISPR 25 Class 5 standard, are shown in Figures 3 and 4, respectively. SSFM can also be enabled in either burst mode or pulse-skipping mode, providing both low EMI and high efficiency.


■ Short circuit protection

The LT8342 has output short-circuit protection to prevent damage in the event of a short circuit. An external sense resistor and an N-channel FET connected in series with the converter input monitor the current and turn off the input when necessary. If the current flowing through the sense resistor exceeds the threshold of the internal comparator, the IC pulls the voltage at the GATE pin to ground, turning off the external FET and limiting the output current caused by the short circuit. The waveforms in Figures 5 and 6 show the typical response of this IC when a short circuit occurs at the output.


An internal hiccup timer counts down for 40ms until the external FET is turned back on. If the short continues, input disconnect is re-enabled when current sense is triggered.



■ Pass-through mode operation

The LT8342 is an excellent choice for automotive preboost applications where the input voltage of the boost converter is higher than the output voltage that is normally being controlled. When this condition occurs, the IC enters PassThru mode. The synchronous power switch located at the top of the IC remains on at 100% duty, and the bottom switch remains off, creating a direct path from input to output. Also, under this condition, the LT8342 enters standby mode, consuming 12 μA when short-circuit protection is not activated, and 26.5 μA when the external input blocking FET is activated. Figure 7 shows the preboost application for stop-start and cold crank, and Figure 8 shows the operation when pass-through mode is enabled.



■ LT8342, small package, low noise, low input current, and other various functions

The LT8342 offers a variety of features including low noise, low input current, excellent efficiency and circuit protection in a small package. With wide input and output ranges, programmable switching frequency, low noise and pass-through mode, this device is ideal for general boost and automotive pre-boost applications. Burst Mode operation and low input quiescent current provide excellent light load efficiency not available in conventional boost converters.

※ About the author
Michael Wu is a product applications engineer at Analog Devices. He works in ADI’s High Performance Power (HPP) group, focusing on monolithic buck, boost, and buck-boost topologies. He received his Master's and Bachelor's degrees in Electrical Engineering from California Polytechnic State University, San Luis Obispo.