LT8645SEV-2 - 65V, 8A Synchronous Silent Switcher Buck | ADI
MPN： LT8645SEV-2 ✓ 啟用中LT8645SEV-2 概覽
What is a synchronous buck (step-down) regulator? It is a switching DC-DC converter that uses both a high-side and a low-side MOSFET (often integrated) to chop the input voltage and average it through an LC filter, producing a lower regulated output rail with much higher efficiency than a linear regulator. Synchronous buck ICs sit inside the broader power-management IC family, alongside LDOs, boost converters, and charge-pump ICs. The "Silent Switcher" architecture adds careful internal layout, optional internal bypass capacitors, and spread-spectrum frequency modulation to suppress switching noise that would otherwise couple into adjacent analog or RF blocks.
Key features include 8A continuous output current, 2.5 µA quiescent current for always-on battery applications, >92% peak efficiency at 12V/5V, integrated 65V internal switches, internal bypass capacitors that reduce EMI, fast minimum on-time of approximately 30 ns for high step-down ratios, and a PGOOD flag, synchronization input, and thermal shutdown. The exposed pad of the 32-TFQFN package gives θJA in the low-30s °C/W range when soldered to adequate PCB copper.
Technically, the LT8645SEV-2 uses current-mode control with internal compensation, supports pulse-skipping and Burst Mode operation for light loads, and includes programmable switching frequency from roughly 200 kHz to 2.2 MHz. The 2.5 µA quiescent current is measured when the output is regulated but unloaded - suitable for automotive battery-direct systems that must stay alive in sleep mode.
Typical applications include automotive always-on systems, industrial 24V/48V bus rails, telecom point-of-load rails, battery-powered portable instruments, and any noise-sensitive system that previously required a bulky EMI input filter ahead of the switching regulator. For high-frequency operation with low EMI, use the internal bypass option and follow the layout reference in the datasheet.
When designing, prioritize a small loop area for the input capacitors and the IC ground return, and provide at least 1 square inch of copper under the exposed pad to manage 8A continuous dissipation. If your design requires higher VIN (>65V) or dual-output capability, look at the LT8646S; if you need 10A, the LT8645S family tops out at 8A on this part number.
直接替換替代品，適用於 LT8645SEV-2 — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： LT8645SEV-2 （相同外形與佔位） — 差異在於 Architecture, Maximum Output Current, Operating Temperature Range, Package, Input Voltage Range.
LT8645SEV#PBF
✅ 直接替換聯絡詢價
查看資料表 →LT8645SEV-2#WPBF
✅ 直接替換📋 參考替代品（不在目錄中）
LT8646SIV#PBF
✅ 直接替換📋 參考替代品（不在目錄中）
LT8645SIV#PBF
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →LT8645SEV-2 最大額定值與電氣特性
| 拓撲 | Synchronous Step-Down (Buck) |
| Architecture | Silent Switcher (2nd generation) |
| 輸入電壓範圍 | 3.4 V to 65 V |
| 輸出電壓範圍 | 0.97 V to VIN (adjustable) |
| 最大輸出電流 | 8 A continuous |
| 靜態電流 | 2.5 µA (no-load, output regulated) |
| 切換頻率 | Programmable ~200 kHz to 2.2 MHz |
| Minimum On-Time | Approx. 30 ns |
| Peak Efficiency | >92% (typ. at 12V→5V) |
| Internal Switches | Integrated high-side + low-side MOSFETs |
| Internal Bypass Capacitors | Yes (EMI reduction) |
| 工作溫度範圍 | -40°C to +125°C |
| 封裝 | 32-TFQFN Exposed Pad (LQFN-32, 5x6 mm) |
| 安裝類型 | Surface Mount |
| PGOOD / SYNC | Power-good flag and synchronization input |
| RoHS 狀態 | Compliant (per #PBF suffix) |
LT8645SEV-2 腳位配置
| 腳位 1 | VIN — Input supply voltage (3.4V to 65V) |
| 腳位 2 | VIN — Input supply voltage (3.4V to 65V) |
| 腳位 3 | VIN — Input supply voltage (3.4V to 65V) |
| 腳位 4 | SW — Switch node (output of internal MOSFETs) |
| 腳位 5 | SW — Switch node (output of internal MOSFETs) |
| 腳位 6 | SW — Switch node (output of internal MOSFETs) |
| 腳位 7 | SW — Switch node (output of internal MOSFETs) |
| 腳位 8 | BST — Bootstrap for high-side gate drive |
| 腳位 9 | PGND — Power ground for internal low-side MOSFET |
| 腳位 10 | PGND — Power ground for internal low-side MOSFET |
| 腳位 11 | PGND — Power ground for internal low-side MOSFET |
| 腳位 12 | PGND — Power ground for internal low-side MOSFET |
| 腳位 13 | AGND — Analog ground reference |
| 腳位 14 | VOUT — Output voltage sense |
| 腳位 15 | FB — Feedback input for output voltage divider |
| 腳位 16 | TR/SS — Timing resistor / soft-start |
| 腳位 17 | RT — Timing resistor for switching frequency |
| 腳位 18 | SYNC — Frequency synchronization input |
| 腳位 19 | PGOOD — Power-good output flag |
| 腳位 20 | EN/UVLO — Enable / undervoltage lockout |
| 腳位 21 | NC — Not connected (per datasheet) |
| 腳位 22 | NC — Not connected (per datasheet) |
| 腳位 23 | NC — Not connected (per datasheet) |
| 腳位 24 | NC — Not connected (per datasheet) |
| 腳位 25 | NC — Not connected (per datasheet) |
| 腳位 26 | NC — Not connected (per datasheet) |
| 腳位 27 | INTERNAL — Internal bypass capacitor (per datasheet) |
| 腳位 28 | INTERNAL — Internal bypass capacitor (per datasheet) |
| 腳位 29 | INTERNAL — Internal bypass capacitor (per datasheet) |
| 腳位 30 | INTERNAL — Internal bypass capacitor (per datasheet) |
| 腳位 31 | PGND — Power ground |
| 腳位 32 | PGND — Power ground |
典型應用
LT8645SEV-2 適用於 6 應用s: Automotive Always-On Systems, Industrial 24V/48V Bus Power, Battery-Powered Portable Instruments, Noise-Sensitive RF and Analog Signal Chains, Point-of-Load Rails for FPGAs and DSPs, Telecom and Networking Equipment.
Automotive Always-On Systems
The LT8645SEV-2 fits automotive always-on body and chassis modules because of its 3.4V to 65V input tolerance, which covers cold-crank and load-dump transients directly off the 12V battery without an upstream preregulator. Its 2.5 µA quiescent current keeps standby drain below 1 mAh per day, satisfying the typical <100 µA sleep-current budget for BCMs, RKE receivers, and CAN/LIN wake-up nodes. Place the IC downstream of the reverse-battery TVS; use 2× 4.7 µF X7R input caps to meet the 8A step-down requirement at 12V→3.3V.
推薦
Industrial 24V/48V Bus Power
Industrial PLCs, factory sensors, and 48V telecom boards all benefit from the LT8645SEV-2's 65V absolute maximum, which provides comfortable margin above 48V nominal plus transient spikes per IEC 61131-2. At 48V→5V the synchronous topology holds >88% efficiency at full load, reducing heatsink requirements versus a linear regulator and shrinking the BOM. The exposed pad of the LQFN-32 package routes heat into the inner copper layers for compact DIN-rail designs.
推薦
Battery-Powered Portable Instruments
Handheld test equipment, medical wearables, and field instruments run on Li-ion or LiFePO4 packs where every microamp of quiescent current extends runtime. The LT8645SEV-2's 2.5 µA IQ and Burst Mode operation allow the regulator to stay alive while the host MCU is in deep sleep, recovering output regulation within microseconds on wake-up. The 30 ns minimum on-time enables direct step-down from a single-cell Li-ion (4.2V max) to 1.0V core rails without an intermediate stage.
推薦
Noise-Sensitive RF and Analog Signal Chains
The Silent Switcher 2 architecture with internal bypass capacitors reduces both conducted and radiated EMI, eliminating the input π-filter that would otherwise be required in front of the converter. This is critical when powering ADCs, DACs, VCOs, or transceivers that sit immediately adjacent on the same PCB. For example, supplying an LMX2492 PLL or an ADC with 5V from the LT8645SEV-2 at 2 MHz switching frequency typically passes CISPR 25 Class 5 without a shielding can.
推薦
Point-of-Load Rails for FPGAs and DSPs
FPGAs and DSPs need multiple low-voltage, high-current rails (0.97V, 1.0V, 1.2V, 1.8V, 3.3V) generated close to the load to minimize IR-drop and PCB trace impedance. The LT8645SEV-2's 8A continuous output and adjustable output down to 0.97V make it a strong POL converter from a 5V or 12V intermediate bus, and the high switching frequency (>1 MHz) allows small ceramic output capacitors. Parallel two LT8645SEV-2s for 16A rails if needed.
推薦
Telecom and Networking Equipment
PoE PDs, base-station RRUs, and 48V network switches all benefit from the 65V input transient tolerance and 8A continuous current of the LT8645SEV-2. It can serve as the main 12V or 5V intermediate bus converter directly from -48V (through a bias supply), or as a downstream POL from a 12V intermediate rail feeding line cards. The exposed pad simplifies thermal design in sealed metal enclosures.
推薦
推薦產品摘要
工程參考資料，適用於 LT8645SEV-2 — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | LT8645SEV#PBF | LT8645SEV-2#WPBF | LT8646SIV#PBF | LT8645SIV#PBF |
|---|---|---|---|---|---|
| Package | 32-TFQFN Exposed Pad | 32-TFQFN Exposed Pad - same | 32-TFQFN Exposed Pad - same | 32-TFQFN Exposed Pad - same | 32-TFQFN Exposed Pad - same |
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Input Voltage Range | 3.4 V to 65 V | 3.4 V to 65 V | 3.4 V to 65 V | 3.4 V to 65 V | 3.4 V to 65 V |
| Output Current | 8 A | 8 A | 8 A | 6 A per channel (dual) | 8 A |
| Silent Switcher Generation | Gen 2 (with internal bypass caps) | Gen 1 (no internal bypass) | Gen 2 | Gen 2 | Gen 2 |
| Number of Outputs | 1 | 1 | 1 | 2 | 1 |
| Automotive Flow (AEC-Q100) | No (standard PBF) | No | Yes (-W automotive flow) | No | No |
主要差異化特點
- Highest current in the LT8645S family at 8A continuous (對比LT8646SIV#PBF)
- Silent Switcher 2 with internal bypass capacitors eliminates input EMI filter (對比LT8645SEV#PBF)
- Automotive-qualified (-W) variant available on the same die (對比LT8645SEV-2#WPBF)
設計說明
The exposed pad of the 32-TFQFN package is the primary thermal path. Solder it to a copper pad of at least 1 square inch (≈ 6 cm²) on the top layer, stitched with 12 thermal vias to the inner ground plane. Without adequate copper, θJA rises above 50 °C/W and 8A continuous operation will trigger thermal shutdown at lower ambient temperatures. The Analog Devices evaluation board (DC2449A) demonstrates the recommended layout.
Place two 4.7 µF X7R 100V ceramic input capacitors within 5 mm of the VIN pins, with their ground returns shorted directly to the PGND pins to form a tight switching loop. The Silent Switcher 2 architecture with internal bypass capacitors dramatically reduces EMI; for CISPR 25 Class 5 conformance, follow the manufacturer reference layout exactly and avoid routing sensitive analog traces under the switch node.
Estimated: at 12V → 5V, 8A continuous, total loss ≈ 12V·8A·(1-η)/η. Assuming η ≈ 92%, PD ≈ 4.9 W. With θJA ≈ 32 °C/W on the evaluation board, junction rise ≈ 157 °C above ambient - too hot for industrial -40 to +125 °C operation without derating. Drop to 5A continuous or reduce VIN-VOUT differential (use a 7V intermediate rail) to keep TJ below 125 °C at 85 °C ambient.
Do not leave BST floating - it requires a 100 nF X7R bootstrap capacitor from BST to SW, placed within 3 mm of the IC. Do not use Y5V or Z5U ceramics for input/output bulk; their capacitance drops 50-80% under DC bias. Do not exceed the absolute maximum VIN of 65V (65V is the operating max; transient capability is rated separately in the datasheet).
合規資訊
RoHS and REACH compliance per the #PBF (lead-free) suffix. AEC-Q100 qualification available only on the -WPBF automotive flow variant; the standard PBF part is not AEC-Q100 qualified. Halogen-free status not explicitly stated in the verified data.
