Introduction to the ADI LT8638S

Introduction to the ADI LT8638S

The ADI LT8638S synchronous buck regulator utilizes the second-generation Silent Switcher architecture to minimize EMI emissions while achieving high efficiency at high switching frequencies. It includes integrated input capacitors to optimize all internal fast current loops and easily advertises EMI performance by reducing layout sensitivity. This performance makes the LT8638S well suited for noise-sensitive applications and environments.

Fast, clean, low overshoot turn-off edges enable high efficiency operation even at high switching frequencies, providing a small overall solution.The LT8638S features peak current mode control with a 25ns minimum on-time, supporting a high step-down ratio even at high switching frequencies. External compensation via the VC pin enables fast transient response. Multi-phase operation allows multiple LT8638S regulators to interleave phase-shifted operation to provide more output current. Burst operation mode enables low standby power consumption, forced continuous mode controls frequency harmonics across the entire output load range, or spread spectrum operation further reduces EMI emissions. Soft-start and tracking functions can be accessed via the SS pin, and the exact input voltage UVLO threshold can be set using the EN/UV pin.

ADI LT8638S Features

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Silent Switcher®2 Architecture

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Ultra-low EMI emissions on any PCB

Eliminates PCB layout sensitivity

Internal bypass capacitor reduces emitted EMI

Optional spread spectrum modulation

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High efficiency at high frequencies

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Up to 96% efficiency at 1MHz, 12VIN to 5VOUT range

Up to 94% efficiency in the 2MHz, 12VIN to 5VOUT range

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Wide input voltage range: 2.8V to 42V

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Maximum continuous output of 10A, peak transient output of 12A

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Reference voltage source accuracy: ±1.0% over full temperature range

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Fast transient response with external compensation

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Low quiescent current Burst Mode® operation

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90µA IQ Regulates 12VIN to 5VOUT

Output ripple < 10mVP-P

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Fast minimum switch-on time: 25ns

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PolyPhase® operation: up to 12 phases

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Low voltage drop under all conditions: 45mV at 1A

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Adjustable and synchronizable: 200kHz to 3MHz

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Output soft start and power supply normal

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Safe for high reverse currents

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28-pin 5mm x 4mm LQFN package

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AEC-Q100 compliant for automotive applications

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ADI LT8638S Application Scenarios and Key Parameters

The LT8638S is primarily used in conventional step-down Buck converters, automotive applications, the medical industry, and industrial applications, and its typical application circuit is shown in the figure below (Figure 1):

Figure 1 LT8638S Typical Application Circuit

The following are LT8638S key parameters:

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Vin: 2.8-42V, Vout: 0.6-40V, Iout: 10A, 12A Peak

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Operating modes: Brust Mode, Forced Continuous Mode, Dither Mode

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Multi-phase operation: Supports multi-phase parallel connection up to 12 phases

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Operating frequency: 200K-3MHz

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LT8638S Rapid Evaluation Board: MCDM8638S

In order to allow customers to more quickly and easily verify the LT8638S, we introduced the MCDM8638S, and ADI Demo DC2929A, MCDM8638S smaller size, with four U-shaped screw holes, easy to assess the thermal performance of the use of two-layer PCB design, lower cost, the output voltage using adjustable potentiometer design, easy to quickly assess a variety of output voltage levels. The output voltage is designed with an adjustable potentiometer to facilitate quick evaluation of various output voltage levels.

MCDM8638S Specifications:

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VIn: 2.8V-42V, Vout: 0.6V-40V continuously adjustable, Iout: 10A/12A Peak

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With four U-shaped screw holes

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Compatible with three inductor sizes

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Supports EN / multi-phase parallel operation

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The following figures (Figures 2 and 3) show the front and back sides of the MCDM8638S physical drawing, respectively:

Figure 2 MCDM8638S physical map front side

 Figure 3 MCDM8638S physical drawing reverse side

The MCDM8638S supports three sizes of inductors, as shown in the figure below (Figure 4), which makes it easy to evaluate the application circuits with different output voltages and operating frequencies. Focusing on conversion efficiency, you can set a lower operating frequency and choose a larger inductor; focusing on the overall board area, you can set a higher operating frequency and choose a smaller inductor.

Figure 4 MCDM8638S supports three sizes of inductors

In addition, the MCDM8638S uses an adjustable potentiometer for the output voltage, as shown in the figure below (Fig. 5), which allows the output voltage to be continuously adjusted. The output voltage can be set from 0.6V to 40V. Since the 3×3 adjustable potentiometer cannot be adjusted to absolute zero ohm, the adjustable potentiometer can be shorted directly if 0.6V output is required.

Figure 5 MCDM8638S Adjustable Potentiometer

summarize

The LT8638S is ADI's high-performance Mos internal power solution based on Silent Switcher®2 technology. The unique physical characteristics of the Silent Switcher®2 architecture give the LT8638S ultra-low EMI noise, ultra-low output ripple, and ultra-low switching losses. The ultra-low switching losses allow the LT8638S to operate at 1-2MHz without excessive loss of efficiency, making the LT8638S ideal for small footprint, high power applications, and noise sensitive devices.

MCDM8638S is a localized demo based on ADI's LT8638S solution, designed according to the power module standard, and can be quickly evaluated by simple wiring and output voltage adjustment after getting it. Moreover, MCDM series can provide complete design information, including PCB/schematic and BOM, which is convenient for engineers to quickly integrate the solution into existing designs.