RT8475GS - 36V 350kHz LED Driver PWM Controller | Richtek
MPN: RT8475GS ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.42 | $0.42 |
| 10 | $0.38 | $3.80 |
| 100 | $0.32 | $32.00 |
| 500 | $0.27 | $135.00 |
| 1,000 | $0.23 | $230.00 |
| 3,000 | $0.2 | $600.00 |
RT8475GS Overview
An LED driver controller is a specialized power management IC that regulates the brightness of solid-state light sources by controlling the current flowing through one or more LEDs. Unlike simple resistor-based current limiters, an LED driver maintains constant current regardless of input voltage variation, temperature drift, or forward-voltage spread between LED batches. The RT8475GS falls into the PWM-controller sub-category of LED drivers (LED driver controller -> LED driver -> power management IC -> semiconductor), where it generates a PWM gate-drive signal for an external switching MOSFET rather than integrating the switch itself - giving designers freedom to choose MOSFET RDS(on), package, and thermal performance for high-power strings.
Key features of the RT8475GS include analog and PWM dimming capability, a 350 kHz typical switching frequency that balances magnetics size against switching loss, and an enable/soft-start pin for controlled startup. The 190 mV low-side current-sense threshold minimizes losses on the sense resistor while preserving regulation, and the wide VIN range (4.5 V to 36 V) accommodates both 5 V/12 V bus systems and 24 V industrial rails. Analog dimming is supported via a linear DIM input, while PWM dimming accepts an external logic signal for high-contrast dimming ratios exceeding 1000:1.
The RT8475GS uses a peak-current-mode control architecture with internal slope compensation, providing good line rejection, simple loop compensation, and cycle-by-cycle current limiting. The external MOSFET topology means designers can scale LED current simply by selecting a lower-inductance sense resistor (RSNS = 190 mV / ILED) - a critical advantage over integrated-switch LED drivers when currents exceed 1 A or when thermal budgets require spreading heat across the PCB rather than concentrating it inside the IC.
Typical applications include high-brightness LED backlighting for LCD panels, architectural and stage lighting, automotive interior/exterior lighting, signage illumination, and DC/DC LED drivers in industrial machine-vision systems. The wide VIN range also suits portable lighting and battery-powered torches when paired with a boost topology.
When designing with this controller, select the external MOSFET and inductor based on peak LED current, switching frequency (350 kHz), and maximum VIN. The sense resistor must be a low-inductance, low-drift type (1% tolerance or better), and the loop bandwidth should remain well below the switching frequency to avoid subharmonic oscillation when operating above 50% duty cycle.
This page synthesizes distributor pricing, drop-in pin-compatible alternatives from the same Richtek controller family, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for RT8475GS — 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 RT8475GS (same form factor and footprint) — differing in Dimming Control, Switching Frequency, Topology.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
RT8475ZS
✅ Drop-In✓ In Stock
$0.42 / Unit
View Datasheet →RT8475GS Maximum Ratings & Electrical Characteristics
| Product Type | LED Driver Controller (PWM Controller for external MOSFET) |
| Topology | Step-Down (Buck), Step-Up (Boost), Buck-Boost |
| Number of Outputs | 1 |
| Input Voltage Range | 4.5 V to 36 V |
| Maximum Output Voltage | 90 V (external MOSFET dependent) |
| Switching Frequency | 350 kHz (typical) |
| Current Sense Threshold | 190 mV |
| Dimming Control | Analog and PWM Dimming |
| Control Method | Current-Mode PWM with Cycle-by-Cycle Current Limit |
| Package | 14-SOP (SOIC-14, 3.9 mm width) |
| Mounting Type | Surface Mount |
| Pin Count | 14 |
| RoHS Status | Compliant |
| Lead-Free | Yes |
RT8475GS Pin Configuration
| Pin 1 | VIN — Input supply voltage (4.5 V to 36 V) |
| Pin 2 | EN/SS — Enable and soft-start control input |
| Pin 3 | DIM — Analog/PWM dimming input |
| Pin 4 | RT — Timing resistor for switching frequency |
| Pin 5 | COMP — Loop compensation node |
| Pin 6 | FB — Feedback voltage input |
| Pin 7 | CS — Current sense input (190 mV threshold) |
| Pin 8 | GND — Ground |
| Pin 9 | DRV — Gate driver output to external MOSFET |
| Pin 10 | VCC — Internal regulator output (bypass cap) |
| Pin 11 | NC — Not connected (per datasheet) |
| Pin 12 | NC — Not connected (per datasheet) |
| Pin 13 | OVP — Over-voltage protection input |
| Pin 14 | BST — Bootstrap supply for high-side driver (topology dependent) |
Typical Applications
RT8475GS is suitable for 6 applications: LCD Backlight LED Driver, Architectural and Stage Lighting, Automotive Interior/Exterior Lighting, Industrial Signage Illumination, Machine Vision LED Lighting, Portable Lighting and Torch Drivers.
LCD Backlight LED Driver
The RT8475GS suits LCD backlight LED strings because it can drive high LED stack voltages (up to 90 V via external MOSFET) from a 12 V or 24 V backlight rail, while the 350 kHz switching frequency keeps the boost inductor small enough to fit beside the panel connector. The 190 mV current-sense threshold supports high LED currents (1-5 A) without dissipating excessive power on the sense resistor, and analog dimming interfaces directly with the panel's brightness control signal.
Recommended
Architectural and Stage Lighting
Architectural lighting fixtures often require driving long LED strings (20-40 LEDs in series) at high current with smooth dimming down to low brightness levels. The RT8475GS external-MOSFET topology handles the high stack voltages, while its PWM dimming input delivers >1000:1 contrast ratio essential for theatre dimming. The wide 4.5-36 V input also accommodates DMX-controlled fixtures powered from 24 V bus rails common in stage rigging.
Recommended
Automotive Interior/Exterior Lighting
The RT8475GS is well-suited for automotive LED applications including daytime running lights, interior ambient lighting, and tail-lamp clusters. With a 36 V maximum input, it tolerates load-dump transients typical of 12 V automotive buses when paired with appropriate TVS protection. The 14-SOP package is footprint-compatible with hand-rework, simplifying prototype builds. Designers should add external automotive-grade MOSFETs qualified to AEC-Q101 for full automotive compliance.
Recommended
Industrial Signage Illumination
Industrial signage and channel-letter illumination requires robust LED drivers that survive wide temperature swings and input voltage fluctuations on factory 24 V rails. The RT8475GS's -40C to +85C operating range and 4.5-36 V input handle these conditions directly. The external-MOSFET architecture allows designers to spread heat across the channel-letter enclosure rather than concentrating it inside the controller IC, extending fixture lifetime.
Recommended
Machine Vision LED Lighting
Machine-vision systems demand high-stability, high-speed LED illumination with precise brightness control. The RT8475GS's analog dimming input accepts a DC voltage for steady-state brightness, while the PWM input supports strobing synchronized with the camera frame rate - critical for reducing motion blur and saving power. The 350 kHz switching frequency is well above typical camera exposure times, eliminating strobing artifacts.
Recommended
Portable Lighting and Torch Drivers
Portable LED torches and worklights benefit from the RT8475GS when used in a boost topology from a single-cell Li-ion battery (3.0-4.2 V) up to 12 V or higher LED stacks. Although minimum VIN is 4.5 V, a small boost pre-regulator can interface seamlessly. The PWM dimming pin accepts button-press logic to step through brightness modes, and the external MOSFET allows high LED currents (3-10 A) without overheating the controller.
Recommended
Recommended Products Summary
Engineering reference data for RT8475GS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | RT8475ZS | LP8869CQPWPRQ1 | AL8860WT-7 |
|---|---|---|---|---|
| Brand | Richtek | Richtek | Texas Instruments | Diodes Incorporated |
| Package | 14-SOP | 14-SOP - same | HTSSOP-14 (different footprint) | TSOT-25 (different footprint) |
| Topology | Buck/Boost/Buck-Boost (controller) | Buck/Boost/Buck-Boost (controller) | Boost (integrated switch) | Buck (integrated switch) |
| Input Voltage Range | 4.5 V to 36 V | 4.5 V to 36 V | 3 V to 40 V | 4.5 V to 40 V |
| Dimming Control | Analog + PWM | Analog + PWM | PWM | PWM + analog (DC) |
| External MOSFET Required | Yes (controller only) | Yes (controller only) | No (integrated) | No (integrated) |
| Maximum Output Voltage | 90 V (MOSFET dependent) | 90 V (MOSFET dependent) | 45 V | 40 V |
Key Differentiators
- Controller-only topology supports highest LED stack voltages (vs AL8860WT-7)
- True analog dimming via linear DIM voltage input (vs LP8869CQPWPRQ1)
- Wide 4.5-36 V input without external pre-regulator (vs RT8475ZS)
Design Notes
Estimated: at 350 kHz switching and 1 A LED current in a boost topology from 12 V to 24 V LED stack, the RT8475GS dissipates roughly 0.3 W (controller only) plus external MOSFET losses. Layout the sense resistor ground return directly to the RT8475GS GND pin using a Kelvin connection - any shared trace inductance between CS and GND will inject switching noise into the current-sense path and cause LED current ripple. Keep the gate-drive trace shorter than 25 mm and use a gate resistor of 10-47 Ohm to control ringing.
Estimated: the 14-SOP package has theta_JA around 80-110 C/W on a 1 oz 2-layer board. Since the controller dissipates relatively little power itself, thermal management focuses on the external MOSFET. Choose a MOSFET with low RDS(on) at the actual VGS driven by the DRV pin (typically 5-10 V), and provide 50-100 mm^2 of copper pour on its drain tab. For continuous LED currents above 3 A in boost topology, consider DPAK or D2PAK MOSFETs.
Three frequent RT8475GS design pitfalls: (1) omitting the BST bootstrap capacitor when used in high-side-drive topologies results in the external MOSFET never turning on properly; (2) selecting a current-sense resistor with too high inductance causes false CS trips and LED flicker - use a dedicated current-sense resistor or a low-ESL chip resistor in Kelvin layout; (3) forgetting the OVP divider network allows the LED stack voltage to exceed the MOSFET VDS rating during open-LED fault conditions. The OVP threshold should be set to 80-90% of the MOSFET's VDS rating.
Compliance Information
RoHS compliant per Richtek product page. Not AEC-Q100 qualified - for automotive applications, pair with AEC-Q101 qualified external MOSFETs. Lead-free terminations per JEDEC J-STD-020.
