LT8645SA

RECOMMENDED FOR NEW DESIGNS

65V, 8A Synchronous Step-Down Silent Switcher 2 with 2.5μA Quiescent Current

Data Sheet (Rev. 0) Product Selection Table

Part Models: 4
1ku List Price: price unavailable

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Overview

Silent Switcher^®2 Architecture

Ultralow EMI Emissions on Any PCB
Eliminates PCB Layout Sensitivity
Internal Bypass Capacitors Reduce Radiated EMI
Optional Spread Spectrum Modulation

High Efficiency at High Frequency

Up to 94% Efficiency at 400kHz, 24V_IN to 5V_OUT
Up to 93% Efficiency at 1MHz, 24V_IN to 5V_OUT

Wide Input Voltage Range: 3.4V to 65V
Wide Output Voltage Range: 0.97V to (V_IN - 0.5V)
Ultralow Quiescent Current Burst Mode Operation

2.5μA I_Q Regulating 12V_IN to 3.3V_OUT (LT8645SA)
Output Ripple < 10mV_P-P

External Compensation: Fast Transient Response and Current Sharing (LT8646SA)
Robust High V_OUT Operation

Safely Tolerates High Reverse Current

Fast Minimum Switch On-Time: 40ns
Low Dropout Under All Conditions: 60mV at 1A
Adjustable and Synchronizable: 200kHz to 2.2MHz
Output Soft-Start and Tracking
Small 32-Lead 6mm × 4mm LQFN Package
AEC-Q100 Qualified for Automotive Applications

The LT^®8645SA/LT8646SA synchronous step-down regulator features second generation Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at high switching frequencies. This includes the integration of bypass capacitors to optimize all the fast current loops inside and make it easy to achieve advertised EMI performance by eliminating layout sensitivity.

The fast, clean, low-overshoot switching edges enable high efficiency operation even at high switching frequencies, leading to a small overall solution size. Peak current mode control with a 40ns minimum ontime allows high step-down ratios even at high switching frequencies. The LT8646SA has external compensation to enable current sharing and fast transient response at high switching frequencies.

Burst Mode^® operation enables ultralow standby current consumption, forced continuous mode can control frequency harmonics across the entire output load range, or spread spectrum operation can further reduce EMI emissions.

APPLICATIONS

Automotive and Industrial Supplies
General Purpose Step-Down

Part Models: 4
1ku List Price: price unavailable

Documentation

Data Sheet 1

LT8645SA/LT8646SA: 65V, 8A Synchronous Step-Down Silent Switcher 2 with 2.5μA Quiescent Current Data Sheet (Rev.0) 10/31/2025

User Guide 1

EVAL-LT8645SA-AZ User Guide: 65V, 8A Synchronous Step-Down Silent Switcher 2 (Rev.0) 10/31/2025

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal. View our quality and reliability program and certifications for more information.

Part Model	Pin/Package Drawing	Documentation	CAD Symbols, Footprints, and 3D Models
LT8645SAAV#PBF	32-Lead LQFN (6mm x 4mm x 0.94mm w/ EP)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LT8645SAAV#TRPBF	32-Lead LQFN (6mm x 4mm x 0.94mm w/ EP)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LT8645SAAV#WPBF	32-Lead LQFN (6mm x 4mm x 0.94mm w/ EP)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LT8645SAAV#WTRPBF	32-Lead LQFN (6mm x 4mm x 0.94mm w/ EP)	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys

This is the most up-to-date revision of the Data Sheet.

Software Resources

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Tools & Simulations

LTpowerCAD

Design tools for the following parts are available in LTpowerCAD:

LT8645S

LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

Evaluation Kits

65V, 8A Synchronous Step-Down Silent Switcher 2

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Product Details

The evaluation circuit EVAL-LT8645SA-AZ is a 65V, 8A synchronous step-down second generation Silent Switcher^® with spread spectrum frequency modulation featuring the LT8645SA. The evaluation board is designed for 5V output from a 5.6V to 65V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8645SA is a compact, ultralow emission, high efficiency, and high speed synchronous monolithic step-down switching regulator. The integrated bypass capacitors optimize all the fast current loops and make it easier to minimize EMI/EMC emissions by reducing layout sensitivity. Selectable spread spectrum mode can further improve EMI/EMC performance. Ultralow quiescent current in Burst Mode® operation achieves high efficiency at very light loads. Fast minimum on-time of 40ns enables high V_IN to low V_OUT conversion at high frequency.

The LT8645SA switching frequency can be programmed either through oscillator resistor or external clock over a 200kHz to 2.2MHz range. The default frequency of EVAL-LT8645SA-AZ is 2MHz. The SYNC pin on the demo board is grounded (JP1 at BURST position) by default for low ripple Burst Mode operation. To synchronize to an external clock, move JP1 to SYNC and apply the external clock to the SYNC terminal. Select the spread spectrum mode and forced continuous mode (FCM), respectively, by moving the JP1 shunt. Figure 1 in the User Guide shows the efficiency of the circuit at 12V input and 24V input in Burst Mode operation (input from V_IN terminal to bypass the EMI filter). Figure 2 shows the LT8645SA temperature rising on EVAL-LT8645SA-AZ board under different load conditions. The rated maximum load current is 8A, while derating is necessary for certain input voltage and thermal conditions. Low switching frequency can extend the output load capability by reducing the power dissipation. Figure 3 in the User Guide shows the temperature rising at 400kHz switching frequency.

Please see the User Guide for the full description.

Resources

EVAL-LT8645SA-AZ - Design Files
10/31/2025

EVAL-LT8645SA-AZ User Guide: 65V, 8A Synchronous Step-Down Silent Switcher 2 (Rev.0)
10/31/2025

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