LT8646 - 65V, 8A Silent Switcher 2 Buck Regulator | Analog Devices
MPN: LT8646 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $9.85 | $9.85 |
| 10 | $8.92 | $89.20 |
| 100 | $7.55 | $755.00 |
| 500 | $6.42 | $3,210.00 |
| 1,000 | $5.18 | $5,180.00 |
LT8646 Overview
A buck (step-down) DC-DC switching regulator is a power management IC that converts a higher DC input voltage to a lower DC output voltage with high efficiency by rapidly switching an internal power MOSFET on and off and filtering the resulting pulse train through an LC network. The LT8646 sits within the Silent Switcher 2 family, which adds internal bypass capacitors and carefully balanced loop nodes to keep the high-frequency switching loops inside the package. Compared with conventional buck converters this drastically reduces radiated EMI, making the part well suited to noise-sensitive automotive, industrial and RF applications.
Key features include 3V to 65V input voltage range (65V abs max), 8A continuous output current with peak load capability, 2.5 µA quiescent current at light load, and internal bypass capacitors that eliminate the need for an external BST diode or capacitor. The regulator supports spread-spectrum frequency modulation and external frequency synchronisation from 200 kHz to 3 MHz. Built-in protection includes internal soft-start, output over-voltage latch-off, and thermal shutdown.
Typical applications include automotive always-on supplies, GSM transceivers, industrial control and 48V telecom point-of-load rails, where high step-down ratios, high current, low EMI, and ultra-low quiescent current are required simultaneously. A typical 12V-to-3.3V/8A design achieves above 95 % efficiency, while a 48V-to-5V/4A conversion reaches above 93 %.
When designing with the LT8646, observe the recommended PCB layout in the datasheet with the exposed pad soldered to a continuous ground plane and input capacitors placed within a few millimetres of the IC. The internal bypass network removes most EMI headaches, but the output inductor and feedback trace routing still warrant attention for clean regulation.
Drop-in alternatives for LT8646 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with LT8646 (same form factor and footprint) — differing in Architecture, Output Voltage Range, Package, Input Voltage Range, Maximum Output Current.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
LT8646SIV#WPBF
✅ Drop-In✓ In Stock
$6.2 / Unit
View Datasheet →LT8646SA
✅ Drop-In📋 Reference alternative (not in catalog)
LT8646SIV#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT8646SEV#WPBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT8645SEV#PBF
✅ Drop-In✓ In Stock
$5.18 / Unit
View Datasheet →LT8646 Maximum Ratings & Electrical Characteristics
| Topology | Synchronous Step-Down (Buck) |
| Input Voltage Range | 3 V to 65 V (65 V abs max) |
| Output Voltage Range | 0.97 V to VIN (adjustable) |
| Maximum Output Current | 8 A continuous |
| Quiescent Current | 2.5 µA (typical at no load) |
| Switching Frequency | 200 kHz to 3 MHz (programmable, synchronisable) |
| Architecture | Silent Switcher 2 with internal bypass capacitors |
| Efficiency | >95 % at 12V to 3.3V/8A |
| Internal MOSFETs | Yes (high-side and low-side integrated) |
| Spread Spectrum | Yes (selectable) |
| Soft-Start | Internal, programmable |
| Output Over-Voltage Protection | Yes (latch-off) |
| Thermal Shutdown | Yes |
| Operating Junction Temperature | -40 °C to +125 °C |
| Package | 32-TFQFN Exposed Pad (5 mm × 6 mm) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
LT8646 32-tfqfn exposed pad (5 mm × 6 mm) Pin Configuration Guide
Pin configuration for LT8646 (32-tfqfn exposed pad (5 mm × 6 mm) package). This power device features gate, drain, and source terminals. For non-polarized packages, refer to the manufacturer datasheet for exact pin 1 orientation and footprint details. Common applications include power supply design, motor driving, and load switching.
No detailed pinout data available for LT8646.
Refer to the datasheet for full pin configuration.
Typical Applications
LT8646 is suitable for 6 applications: Automotive Always-On Supplies, GSM/LTE Transceiver Power, Industrial 24 V / 48 V Point-of-Load, 48 V Telecom and Datacenter POL, Solar Microinverter Auxiliary Rails, Medical Imaging and Diagnostic Equipment.
Automotive Always-On Supplies
Why the LT8646 fits: with a 65 V input rating it survives 12 V load-dump transients up to 40 V without external protection, and its 2.5 µA quiescent current keeps parasitic battery drain at a minimum on always-on rails such as body control modules. The Silent Switcher 2 architecture passes CISPR 25 Class 5 EMI without complex shielding, which shortens automotive qualification cycles. Used as: a 12 V-to-3.3 V/4 A supply for ECU microcontrollers and CAN transceivers. Performance note: 8 A capability also allows the same hardware to power body-control motors during cranking without dropout.
Recommended
GSM/LTE Transceiver Power
Why the LT8646 fits: GSM/LTE transceivers require low-noise power rails with high peak currents during transmit bursts, and the LT8646's 8 A output and 200 kHz–3 MHz switching frequency let it stay outside the sensitive RF bands. The 2.5 µA quiescent current minimises standby drain when the modem is idle. Used as: a 4.2 V Li-ion to 3.8 V/5 A rail for the RF power amplifier and transceiver. Performance note: ultra-low output ripple (~10 mV pk-pk) avoids desensitising the receiver, while above 95 % efficiency extends talk time.
Recommended
Industrial 24 V / 48 V Point-of-Load
Why the LT8646 fits: industrial PLCs and process controllers commonly run on 24 V rails with transients up to 60 V, well within the LT8646's 65 V abs-max input. The 8 A output current and adjustable 0.97 V to VIN output support a wide range of digital logic rails (3.3 V, 5 V, 12 V). Used as: a 24 V-to-5 V/6 A intermediate bus for downstream point-of-load converters feeding FPGA or DSP rails. Performance note: 2.5 µA IQ supports sleep-mode operation, while thermal shutdown protects against fan-failure events in control cabinets.
Recommended
48 V Telecom and Datacenter POL
Why the LT8646 fits: 48 V telecom and datacentre intermediate bus architectures need high step-down ratios from 48 V to 1 V–5 V at multi-amp currents with high efficiency. The LT8646's 65 V abs-max comfortably exceeds the 48 V rail plus transients, while its 8 A continuous output serves as a building block for distributed POLs. Used as: a 48 V-to-5 V/4 A bus converter feeding downstream buck regulators. Performance note: above 93 % efficiency at 48 V input reduces cooling requirements in dense server racks.
Recommended
Solar Microinverter Auxiliary Rails
Why the LT8646 fits: solar microinverters generate high DC bus voltages that can exceed 60 V under no-load conditions, and the LT8646's 65 V abs-max handles this directly without pre-regulation. The 8 A output and high efficiency reduce thermal stress in outdoor enclosures, while ultra-low IQ minimises night-time losses to maximise panel-level efficiency. Used as: a 48 V-to-12 V/3 A auxiliary rail for gate drivers and control logic. Performance note: spread-spectrum switching and internal bypass capacitors help meet conducted and radiated EMI standards without bulky input filters.
Recommended
Medical Imaging and Diagnostic Equipment
Why the LT8646 fits: medical imaging systems such as ultrasound and patient monitors need clean, low-EMI power rails to avoid interfering with sensitive analog front-ends and sensor channels. The Silent Switcher 2 architecture of the LT8646 keeps switching noise below 10 mV pk-pk on the output, while the wide 3–65 V input simplifies integration with battery stacks or AC-derived 24 V rails. Used as: a 24 V-to-5 V/5 A supply for ADC, DSP and display backlight rails. Performance note: the 2.5 µA quiescent current extends battery runtime on portable carts and patient wearables between recharge cycles.
Recommended
Recommended Products Summary
Engineering reference data for LT8646 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LT8646S | LT8646SA | LT8646SIV#PBF | LT8646SEV#WPBF | LT8645S |
|---|---|---|---|---|---|---|
| Package | 32-TFQFN Exposed Pad (5x6 mm) | 32-TFQFN Exposed Pad - same | 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 | Analog Devices |
| Input Voltage Range | 3 V to 65 V | 3 V to 65 V | 3 V to 65 V | 3 V to 65 V | 3 V to 65 V | 3 V to 65 V |
| Output Current | 8 A | 8 A | 8 A | 8 A | 8 A | 6 A |
| Quiescent Current | 2.5 µA | 2.5 µA | 2.5 µA | 2.5 µA | 2.5 µA | 2.4 µA |
| Architecture | Silent Switcher 2 | Silent Switcher 2 | Silent Switcher 2 (SS variant) | Silent Switcher 2 | Silent Switcher 2 | Silent Switcher 2 |
| Switching Frequency Range | 200 kHz to 3 MHz | 200 kHz to 3 MHz | 200 kHz to 3 MHz | 200 kHz to 3 MHz | 200 kHz to 3 MHz | 200 kHz to 3 MHz |
| Automotive Grade (AEC-Q100) | No | No | No | No (Industrial) | Yes | No |
Key Differentiators
- Higher continuous output current than the LT8645S (vs LT8645S)
- Automotive-grade variant available in the same package (vs LT8646SIV#PBF)
- Spread-spectrum-only variant for fixed-frequency-sensitive systems (vs LT8646S)
Design Notes
Estimated: the exposed pad carries both thermal and electrical ground and must be soldered to a continuous ground copper pour of at least 25 mm² to keep θJA below 30 °C/W. Place the input ceramic capacitors (typically 2 × 4.7 µF X7R) within 2 mm of the VIN and PGND pins, and keep the SW trace short and wide to minimise AC loop area. The internal bypass capacitors mean most EMI layout is taken care of, but output inductor placement still matters: keep it away from sensitive analog traces.
At VIN = 24 V, VOUT = 5 V, and IOUT = 8 A, estimated power dissipation is (24 − 5) × 8 = 152 W in theory, but in practice the synchronous-rectifier topology reduces this dramatically: actual dissipation is roughly VIN × IQ + (VOUT × IOUT × (1/η − 1)) ≈ 4 W at above 95 % efficiency. With θJA around 30 °C/W on a well-laid-out 4-layer PCB the junction temperature rise is 120 °C above 25 °C ambient, so a cold-air flow or copper heat-spreader is recommended for sustained 8 A output above 60 °C ambient.
Do not exceed the 65 V absolute maximum input voltage — even brief transients above this can permanently damage the internal MOSFETs. The TR/SS capacitor must not be omitted; it controls startup inrush and a missing cap can trigger false OVP latch-off on power-up. Avoid routing the FB trace near the SW node; use a Kelvin connection to the top of the feedback resistor divider and shield it with a ground pour for clean regulation.
Compliance Information
RoHS compliant per Analog Devices product page (LT8646SIV#PBF is Pb-free). AEC-Q100 qualification available on the LT8646SEV#WPBF automotive W grade only. Halogen-free status not stated in the verified data — set to unknown.
