STR-C3501
High-efficiency buck-boost converter with seamless mode transition, ideal for battery-powered applications with
Product Overview
Description
The STR-C3501 is a synchronous buck-boost converter designed for applications with variable input voltage.
It seamlessly transitions between buck and boost modes as input voltage varies above and below the output.
The IC is ideal for battery-powered applications where input voltage changes during discharge.
Product Series
STR
Primary Application
Battery-powered devices
Key Features
- Seamless buck-boost operation
- Wide input voltage range (2.5V-14V)
- High efficiency up to 95%
- 1MHz switching frequency
- Low RDS(on) integrated MOSFETs
- Programmable output voltage
- Power good indicator
- Compact QFN package
Specifications
| Input Voltage | 2.5V to 14V |
|---|---|
| Output Voltage | 2.5V to 14V (configurable) |
| Max Output Current | 2A |
| Max Output Power | 15W |
| Efficiency | Up to 95% |
| Switching Frequency | 1MHz |
| Package | QFN-16 (3x3mm) |
| Operating Temperature | -40°C to +85°C |
Applications
Battery-powered devices
Battery and charging management
Portable electronics
Electronic system design
Power banks
Electronic system design
Industrial handheld devices
Industrial automation and control
Wireless communication devices
Communication and interface
FAE Expert Insights
"The STR-C3501 is an excellent choice for battery-powered designs requiring stable output regardless of battery voltage. The seamless mode transition is truly seamless - there's no glitch or instability when crossing the buck-boost boundary. I've used this in several single-cell lithium battery designs where the output needs to be regulated at 3.3V or 5V as the battery discharges from 4.2V to 3.0V. The efficiency remains high across the entire battery voltage range. The 1MHz switching allows for compact inductor size. For battery-powered products, this converter provides reliable, efficient performance."
Seamless buck-boost with wide input range for battery applications
— Robert Zhang, BeiLuo
Frequently Asked Questions
How does the seamless buck-boost transition work?
The STR-C3501 uses a 4-switch H-bridge topology that automatically reconfigures based on the input-output voltage relationship. When Vin > Vout, it operates in buck mode with the buck switches active. When Vin < Vout, it operates in boost mode with the boost switches active. The transition between modes happens automatically based on voltage comparison, with no output disturbance. The control loop maintains stable output regulation throughout the entire input voltage range.
Seamless transition is automatic. No external control needed. Ideal for battery applications.
What battery configurations work with STR-C3501?
STR-C3501 works with various battery configurations due to its wide 2.5V-14V input range. For single-cell lithium (3.0V-4.2V), it can produce regulated 3.3V or 5V output. For 2S lithium (6V-8.4V), it can produce 5V or 12V output. For 3S lithium (9V-12.6V), it can produce 12V output. The converter maintains regulation throughout the battery discharge curve, maximizing usable battery capacity.
Works with 1S to 3S lithium batteries. Select output voltage based on application needs.
What is the efficiency in buck vs boost mode?
Efficiency varies between buck and boost modes due to different current paths and switch configurations. Buck mode typically achieves slightly higher efficiency (93-95%) because current flows through fewer switches. Boost mode efficiency is typically 90-93% due to higher switch currents. The efficiency is optimized for each mode through the control algorithm. Overall efficiency across the input voltage range remains high, making it suitable for battery applications where input voltage varies.
Efficiency is high in both modes. Expect 90-95% depending on operating point.
How do I set the output voltage on STR-C3501?
Output voltage is set using external resistor dividers connected to the FB pin. The feedback reference voltage is typically 1.0V or 0.8V depending on the specific variant. Calculate resistor values using the standard voltage divider formula. Place feedback resistors close to the IC and keep the FB trace short. The datasheet provides recommended resistor values for common output voltages. Some variants may support I2C or other digital interfaces for voltage adjustment.
Use resistor dividers for fixed outputs. Check datasheet for reference voltage.
What inductor value should I use?
The recommended inductor value depends on the switching frequency and desired ripple current. For the STR-C3501's 1MHz switching frequency, a 2.2μH inductor is typically recommended for 2A applications. The inductor should have saturation current rating above the maximum peak current (typically 1.2-1.5x output current). Low DCR is important for efficiency. Shielded inductors are recommended to minimize EMI. The datasheet provides detailed inductor selection guidelines.
Use 2.2μH for typical applications. Ensure adequate saturation current rating.
Can STR-C3501 handle load transients well?
Yes, STR-C3501 includes internal compensation optimized for good transient response. The 1MHz switching frequency allows fast response to load changes. For applications with large load transients, additional output capacitance may be needed to limit voltage droop or overshoot. The power good (PG) output can be used to signal when the output is in regulation after a transient event. For critical applications, test transient response under actual operating conditions.
Good transient response with internal compensation. Add output capacitance for large load steps.