SLM3400
Silan SLM3400 high-efficiency synchronous buck DC-DC converter with wide input range and adjustable output for voltag...
Product Overview
Description
The SLM3400 is a high-efficiency synchronous buck DC-DC converter for voltage step-down applications.
Features wide input voltage range and adjustable output voltage with excellent load regulation.
Integrated high-side and low-side MOSFETs provide high efficiency and compact solution size.
Product Series
SLM
Primary Application
Industrial power supplies
Key Features
- Wide input voltage: 4.5V to 36V
- Up to 3A output current
- Adjustable output: 0.8V to 30V
- Integrated 80mΩ/40mΩ MOSFETs
- Fixed 500kHz switching frequency
- Soft start and thermal protection
Specifications
Applications
Industrial power supplies
Industrial automation and control
Battery-powered systems
Battery and charging management
Point-of-load regulation
Power conversion and supply
Automotive electronics
Automotive and EV electronics
FAE Expert Insights
"The SLM3400 is my recommended buck converter for industrial and automotive applications. The 4.5V-36V input range covers 12V and 24V industrial buses with margin for transients. I've used this in numerous PLC I/O modules and sensor power supplies. The integrated synchronous MOSFETs provide 92-95% efficiency, much better than non-synchronous alternatives. One 24V to 5V/2A design achieved 94% efficiency with minimal heating. The 500kHz switching allows use of small inductors (10-22μH) while maintaining good efficiency. Current limiting is accurate and repeatable - important for protecting downstream circuits. For automotive applications, the 36V rating handles load dump transients. The adjustable output (0.8V-30V) makes this very flexible. Overall, an excellent general-purpose buck converter."
High efficiency and wide input range for industrial applications
— 刘建国, BeiLuo
Frequently Asked Questions
How do I set the output voltage for SLM3400?
The SLM3400 output voltage is set using a resistor divider from Vout to FB pin to GND: Vout = 0.8V × (1 + R1/R2), where 0.8V is the internal reference voltage. R1 is top resistor from Vout to FB, R2 is bottom resistor from FB to GND. (1) Choose R2 value - typically 10kΩ for moderate current draw. (2) Calculate R1: R1 = R2 × (Vout/0.8V - 1). (3) Example: For 5V output with R2=10kΩ: R1 = 10k × (5/0.8 - 1) = 52.5kΩ. Use standard 52.3kΩ or 53.6kΩ. (4) Precision - use 1% tolerance resistors for accurate output voltage. (5) Compensation - add feedforward capacitor (10-100pF) across R1 for improved transient response. The FB pin is high impedance, keep trace short and away from switching nodes to prevent noise pickup.
Use 10kΩ for R2, calculate R1 using formula; add 22pF feedforward cap for stability.
What inductor value should I use with SLM3400?
Inductor selection for SLM3400 buck converter: L = (Vout × (Vin - Vout)) / (Vin × fsw × ΔIL), where fsw = 500kHz and ΔIL is inductor ripple current (typically 30% of Iout). (1) Example: 5V output from 12V input at 3A: L = (5 × (12-5)) / (12 × 500k × 0.9) = 6.5μH. Use standard 6.8μH or 10μH. (2) Ripple trade-off - higher inductance reduces ripple but increases size and DCR. Lower inductance allows smaller size but increases ripple. (3) Current rating - select inductor with saturation current >1.5× maximum load current. For 3A load, use 5A+ rated inductor. (4) DCR - lower DCR improves efficiency. Target <30mΩ for 3A applications. (5) Recommended values: 10μH for 1-2A, 6.8μH for 2-3A, 4.7μH for >3A applications.
Use 10μH for most applications; 6.8μH for higher current.
How do I calculate power dissipation in SLM3400?
SLM3400 power dissipation consists of conduction losses and switching losses: (1) Conduction loss - Pcond = Iout² × (Rds_high × D + Rds_low × (1-D)), where D = Vout/Vin is duty cycle. (2) Switching loss - Psw = 0.5 × Vin × Iout × (tr + tf) × fsw, where tr/tf are rise/fall times (~10ns). (3) Example: 5V/3A from 12V: D = 5/12 = 0.42. Pcond = 9 × (0.08×0.42 + 0.04×0.58) = 0.51W. Psw = 0.5 × 12 × 3 × 20ns × 500k = 0.18W. Total = 0.69W. (4) Quiescent current - add ~10mW for IC operation. (5) Efficiency = Pout / (Pout + Ploss) = 15W / 15.7W = 95.5%. Thermal design: with θja = 40°C/W (ESOP-8 with copper), temperature rise = 0.69 × 40 = 27.6°C.
Calculate both conduction and switching losses; ensure adequate PCB copper for heat dissipation.
What input and output capacitors are recommended?
Capacitor selection for SLM3400: (1) Input capacitor - use ceramic capacitors (X5R or X7R) with low ESR. Recommended: 22μF + 0.1μF ceramic. Place close to Vin and GND pins. Voltage rating >1.5× Vin max. (2) Output capacitor - affects output ripple and transient response. Recommended: 22-100μF ceramic or 100-470μF electrolytic with 10μF ceramic in parallel. (3) Ripple calculation - Vripple = ΔIL × (ESR + 1/(8×fsw×Cout)). Lower ESR and higher Cout reduce ripple. (4) Transient response - larger Cout improves load transient response. Use 100μF+ for large load steps. (5) Stability - minimum 10μF ceramic required for stable operation. Avoid tantalum capacitors on output due to ESR variations.
Use 22μF ceramic input, 47μF ceramic output for most applications.
Can SLM3400 operate at 100% duty cycle?
The SLM3400 has a maximum duty cycle of approximately 90-95% (typical 98% min guaranteed). This means: (1) Dropout voltage - when Vin approaches Vout, the converter cannot maintain regulation. Minimum Vin = Vout / 0.95 + margin. (2) Example: For 5V output, minimum Vin ≈ 5.3V. Below this, output follows input minus drop across high-side MOSFET and inductor DCR. (3) Low dropout applications - if dropout operation is required, consider using an LDO after the buck converter, or select a converter with 100% duty cycle capability. (4) Startup - during startup, duty cycle gradually increases from 0% to operating point. (5) Current limit - still active during dropout to protect against shorts. For applications requiring operation down to Vin = Vout + 0.5V, consider Silan's SLM3450 with 100% duty cycle capability.
Minimum Vin is Vout/0.95; use LDO for lower dropout requirements.
How do I synchronize multiple SLM3400 converters?
The SLM3400 does not have external synchronization capability - it uses internal fixed 500kHz oscillator. For applications requiring synchronization: (1) Independent operation - multiple SLM3400s can operate independently without synchronization. Beat frequencies may occur but are usually not problematic. (2) Phase interleaving - not supported by SLM3400. Consider external controllers for multi-phase applications. (3) External sync alternative - use Silan's SLM3420 which supports external synchronization input. (4) EMI considerations - if beat frequencies cause EMI issues, add input filtering or use synchronized controllers. (5) Layout - keep switching nodes of independent converters separated to prevent magnetic coupling. For most applications, independent operation of multiple SLM3400s works well without synchronization.
SLM3400 does not support sync; use independently or consider SLM3420 for sync requirements.