Overview
The LM3485MMX/NOPB, produced by Texas Instruments, is a high-efficiency PFET switching buck regulator controller. This device is designed to simplify the development of small, low-cost switching buck regulators for a wide range of applications. The LM3485 utilizes a hysteretic control architecture, which eliminates the need for control-loop compensation, making it easy to use and design with. It supports a wide input voltage range of 4.5 V to 35 V and can adjust the output voltage from 1.242 V to the input voltage level. The controller is known for its high efficiency, achieving up to 93% efficiency, and its ability to operate at 100% duty cycle, which is beneficial for ultralow dropout applications.
Key Specifications
| Parameter | Minimum | Typical | Maximum | Unit |
|---|---|---|---|---|
| Supply Voltage | 4.5 | - | 35 | V |
| Operating Junction Temperature | -40 | - | 125 | °C |
| Output Voltage Range | 1.242 | - | VIN | V |
| Feedback Voltage | 1.217 | 1.242 | 1.267 | V |
| Comparator Hysteresis | 10 | 15 | 20 | mV |
| Quiescent Current at Ground Pin | 250 | 400 | - | µA |
| Maximum Operating Frequency | - | - | > 1 MHz | - |
| Junction-to-Ambient Thermal Resistance | - | - | 163.3 | °C/W |
Key Features
- Easy-to-Use Control Methodology: The LM3485 uses a hysteretic control scheme that does not require control-loop compensation, simplifying the design process.
- Wide Input Voltage Range: Supports input voltages from 4.5 V to 35 V.
- Adjustable Output Voltage: The output voltage can be set from 1.242 V to the input voltage level using two external resistors.
- High Efficiency: Achieves up to 93% efficiency and operates at 100% duty cycle for ultralow dropout applications.
- Current Limit Protection: Includes a current limit protection circuit that turns the PFET off for approximately 9 µs when the inductor current is too high.
- Low Component Count: The PFET architecture allows for a low component count and simple design.
Applications
The LM3485 is suitable for a variety of applications requiring efficient and compact DC-DC conversion. These include:
- Portable Electronics: Such as smartphones, tablets, and laptops where space and efficiency are critical.
- Industrial Power Supplies: For applications requiring reliable and efficient power conversion.
- Automotive Systems: Where the wide input voltage range and high efficiency are beneficial.
- Consumer Electronics: Including set-top boxes, gaming consoles, and other devices that require efficient power management.
Q & A
- What is the input voltage range of the LM3485?
The LM3485 supports an input voltage range of 4.5 V to 35 V.
- How is the output voltage adjusted on the LM3485?
The output voltage can be adjusted using two external resistors connected to the feedback pin (FB) and the adjust pin (ADJ).
- What is the maximum operating frequency of the LM3485?
The LM3485 can operate at frequencies greater than 1 MHz.
- Does the LM3485 require control-loop compensation?
No, the LM3485 uses a hysteretic control scheme that does not require control-loop compensation.
- What is the typical efficiency of the LM3485?
The LM3485 can achieve up to 93% efficiency.
- How does the current limit protection work on the LM3485?
The current limit protection circuit turns the PFET off for approximately 9 µs when the inductor current exceeds the set limit.
- What is the junction-to-ambient thermal resistance of the LM3485 in the VSSOP package?
The junction-to-ambient thermal resistance is 163.3 °C/W.
- Can the LM3485 operate at 100% duty cycle?
- What are the typical operating modes of the LM3485?
The LM3485 operates in either continuous conduction mode (CCM) at heavy loads or discontinuous conduction mode (DCM) at light loads.
- How does the feed-forward capacitor (Cff) affect the operation of the LM3485?
The feed-forward capacitor (Cff) influences the operating frequency and output ripple voltage by sourcing or sinking current through it, affecting the hysteretic operation.
