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RT8475ZS LED Driver Controller - Equivalent & Substitute Parts
Part Overview
The RT8475ZS is a LED Driver IC manufactured by Richtek USA Inc., classified as a Power Management (PMIC) device. This 14-SOP surface mount controller integrates step-down (buck) and step-up (boost) topologies with analog and PWM dimming capabilities, designed for backlight and lighting applications. The device operates across a 4.5V to 36V supply range with a 350kHz switching frequency and supports output voltages up to 90V.
The RT8475ZS carries a "Not For New Designs" product status, indicating it is obsolete or in end-of-life phase. This status necessitates identification of active, functionally equivalent substitute components to ensure design continuity and long-term supply chain reliability for new and ongoing production applications.
Substiute Parts
Key Parameters
| Parameter | RT8475ZS Value |
|---|---|
| Manufacturer | Richtek USA Inc. |
| Category | Power Management (PMIC) |
| Type | DC DC Controller |
| Topology | Step-Down (Buck), Step-Up (Boost) |
| Number of Outputs | 1 |
| Voltage - Supply (Min) | 4.5V |
| Voltage - Supply (Max) | 36V |
| Voltage - Output | 90V |
| Frequency | 350kHz |
| Dimming | Analog, PWM |
| Operating Temperature | -40°C ~ 125°C (TJ) |
| Mounting Type | Surface Mount |
| Package / Case | 14-SOIC (0.154", 3.90mm Width) |
| RoHS Status | ROHS3 Compliant |
| MSL Rating | 3 (168 Hours) |
Substitute Part Grouping Explanation
Substitute parts for the RT8475ZS are identified based on the following critical parameters that determine functional equivalence:
Primary Substitution Criteria:
- DC DC Controller type with single output
- Dual topology support (Step-Down Buck and Step-Up Boost)
- Analog and PWM dimming capability
- Supply voltage range compatibility (minimum 4.5V, maximum ≥36V)
- Output voltage capability (≥90V)
- Operating temperature range (-40°C to ≥125°C)
- Surface mount packaging
- ROHS3 compliance
Secondary Compatibility Factors:
- Switching frequency in the range of 200kHz to 2MHz
- Lighting and backlight application suitability
- Active product status (preferred for new designs)
- Moisture sensitivity level and thermal performance
The substitute parts listed below meet these criteria with varying package configurations and enhanced specifications. Parts are grouped by topology match and active product status.
Parameter Comparison
| Parameter | RT8475ZS | LT3791HFE#TRPBF | LT3791IFE#PBF | LT3791IFE#TRPBF | LT8391AHFE#PBF | LT8391AHUFD#TRPBF | LT8391IFE#TRPBF | LT3743EFE#TRPBF |
|---|---|---|---|---|---|---|---|---|
| Manufacturer | Richtek USA Inc. | Analog Devices Inc. | Analog Devices Inc. | Analog Devices Inc. | Analog Devices Inc. | Analog Devices Inc. | Analog Devices Inc. | Analog Devices Inc. |
| Type | DC DC Controller | DC DC Controller | DC DC Controller | DC DC Controller | DC DC Controller | DC DC Controller | DC DC Controller | DC DC Controller |
| Topology | Buck, Boost | Buck, Boost | Buck, Boost | Buck, Boost | Buck, Boost | Buck, Boost | Buck, Boost | Buck |
| Number of Outputs | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| Voltage - Supply (Min) | 4.5V | 4.7V | 4.7V | 4.7V | 4V | 4V | 4V | 6V |
| Voltage - Supply (Max) | 36V | 60V | 60V | 60V | 60V | 60V | 60V | 36V |
| Voltage - Output | 90V | 0V ~ 60V | 0V ~ 60V | 0V ~ 60V | 60V | 60V | 60V | — |
| Frequency | 350kHz | 200 ~ 700kHz | 200 ~ 700kHz | 200 ~ 700kHz | 600kHz ~ 2MHz | 600kHz ~ 2MHz | 150kHz ~ 650kHz | 200kHz ~ 1MHz |
| Dimming | Analog, PWM | Analog, PWM | Analog, PWM | Analog, PWM | Analog, PWM | Analog, PWM | Analog, PWM | PWM |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 150°C | -40°C ~ 125°C | -40°C ~ 125°C | -40°C ~ 150°C | -40°C ~ 150°C | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount |
| Package / Case | 14-SOIC | 38-TSSOP-EP | 38-TSSOP-EP | 38-TSSOP-EP | 28-TSSOP-EP | 28-QFN (4x5) | 28-TSSOP-EP | 28-TSSOP-EP |
| Product Status | Not For New Designs | Active | Active | Active | Active | Active | Active | Active |
| RoHS Status | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant |
| MSL Rating | 3 (168 Hours) | 1 (Unlimited) | 1 (Unlimited) | 1 (Unlimited) | 1 (Unlimited) | 1 (Unlimited) | 1 (Unlimited) | 1 (Unlimited) |
Engineering Selection Recommendations
Primary Substitutes (Full Topology Match - Buck and Boost):
The LT3791 series (LT3791HFE#TRPBF, LT3791IFE#PBF, LT3791IFE#TRPBF) and LT8391 series (LT8391AHFE#PBF, LT8391AHUFD#TRPBF, LT8391IFE#TRPBF) from Analog Devices Inc. provide the closest functional equivalence to the RT8475ZS. All are active products with ROHS3 compliance and support dual buck-boost topologies with analog and PWM dimming.
The LT3791 variants operate at -40°C to 125°C or 150°C with 200-700kHz frequency range and 0V to 60V output capability. The LT8391 variants extend the frequency range to 150kHz-2MHz and support automotive-grade qualification (LT8391AHFE#PBF, LT8391AHUFD#TRPBF, LT8391IFE#TRPBF). Package options include 38-TSSOP-EP (LT3791 series) and 28-TSSOP-EP or 28-QFN (LT8391 series).
Secondary Substitute (Buck Topology Only):
The LT3743EFE#TRPBF from Analog Devices Inc. provides buck-only topology with PWM dimming, active product status, and ROHS3 compliance. This part is suitable only for applications requiring step-down conversion without boost capability. Operating range is -40°C to 125°C with 200kHz-1MHz frequency and 28-TSSOP-EP packaging.
Compliance and Availability:
All substitute parts maintain ROHS3 compliance and REACH unaffected status, matching the regulatory profile of the RT8475ZS. The LT3791 and LT8391 series offer superior moisture sensitivity ratings (MSL 1 vs. MSL 3), providing enhanced reliability for storage and handling. Active product status ensures long-term availability and design support.
Frequently Asked Questions (FAQ)
Q: Can the LT3791HFE#TRPBF directly replace the RT8475ZS in existing designs?
A: The LT3791HFE#TRPBF matches the RT8475ZS in topology (buck-boost), dimming capability (analog and PWM), and operating temperature range (-40°C to 125°C). However, the package differs (38-TSSOP-EP vs. 14-SOIC), requiring PCB layout redesign. The LT3791 supports higher supply voltage (60V max vs. 36V) and output voltage (0-60V vs. 90V), which may require application-specific evaluation. Pin configuration and control interface must be verified against the original design schematic.
Q: Why do the LT8391 variants show automotive qualification while the RT8475ZS does not?
A: The LT8391AHFE#PBF, LT8391AHUFD#TRPBF, and LT8391IFE#TRPBF carry AEC-Q100 automotive qualification and automotive-grade designation. This indicates these parts meet automotive industry reliability and testing standards. The RT8475ZS does not list automotive qualification. For non-automotive applications, this difference is not a limiting factor. For automotive designs, the LT8391 automotive variants provide additional qualification assurance.
Q: What is the significance of the MSL rating difference between RT8475ZS and substitute parts?
A: The RT8475ZS has MSL 3 (168 hours), while most LT3791 and LT8391 variants have MSL 1 (unlimited). MSL rating indicates moisture sensitivity during storage and handling. MSL 1 parts have no time-based moisture absorption limits, providing greater flexibility in inventory management and reducing risk of moisture-induced failures during assembly. For high-volume or long-term storage applications, MSL 1 parts offer operational advantages.
Q: Can the LT3743EFE#TRPBF substitute for the RT8475ZS in all applications?
A: The LT3743EFE#TRPBF supports only buck (step-down) topology, whereas the RT8475ZS supports both buck and boost topologies. This part is suitable only for applications that require step-down conversion exclusively. If the design requires boost capability or voltage regulation above the input supply level, the LT3743 is not a valid substitute. Verify application requirements before selection.
Q: What packaging considerations apply when selecting a substitute?
A: The RT8475ZS uses 14-SOIC (0.154", 3.90mm width) packaging. Substitute parts use larger packages: LT3791 series in 38-TSSOP-EP, LT8391 series in 28-TSSOP-EP or 28-QFN (4x5). Larger packages require PCB redesign, increased board space, and modified thermal management. The 28-QFN option (LT8391AHUFD#TRPBF) offers a more compact footprint than TSSOP variants. Package selection depends on available PCB real estate and thermal dissipation requirements.
Q: Are all substitute parts ROHS3 compliant?
A: Yes. All listed substitute parts (LT3791 series, LT8391 series, and LT3743EFE#TRPBF) carry ROHS3 compliance status, matching the RT8475ZS regulatory requirement. All parts are also REACH unaffected, ensuring compliance with European chemical regulations.
Q: What frequency range differences exist between the RT8475ZS and substitutes?
A: The RT8475ZS operates at a fixed 350kHz frequency. Substitute parts offer programmable or fixed frequency ranges: LT3791 series (200-700kHz), LT8391 series (150kHz-2MHz or 600kHz-2MHz), and LT3743 (200kHz-1MHz). Programmable frequency allows optimization for specific application requirements, including EMI performance and component sizing. Fixed frequency designs may require external frequency-setting components.
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