Overview
The LM3485 is a high-efficiency PFET switching regulator controller designed by Texas Instruments (formerly National Semiconductor). It is used to develop small, low-cost, switching buck regulators for a wide range of applications. The LM3485 features a hysteretic control architecture, which simplifies the design process by eliminating the need for control-loop stability concerns. This architecture allows for low component count, ultralow dropout, and 100% duty cycle operation, making it highly efficient even at light loads without increasing output ripple.
Key Specifications
| Parameter | Min | Max | Unit | |
|---|---|---|---|---|
| Supply Voltage | 4.5 | - | 35 | V |
| Operating Junction Temperature | -40 | - | 125 | °C |
| Output Voltage Range | 1.242 | - | VIN | V |
| Internal Reference Accuracy | ±1.3% (±2% Over Temp) | - | - | % |
| Maximum Operating Frequency | - | - | > 1 MHz | - |
| Junction-to-Ambient Thermal Resistance | - | - | 163.3 | °C/W |
| Package Type | - | - | VSSOP (8 pins) | - |
Key Features
- Easy-to-Use Control Methodology
- No Control-Loop Compensation Required
- 4.5-V to 35-V Wide Input Range
- 1.242-V to VIN Adjustable Output Range
- High Efficiency (up to 93%)
- ±1.3% (±2% Over Temp) Internal Reference
- 100% Duty Cycle
- Maximum Operating Frequency > 1 MHz
- Current Limit Protection
Applications
- Set-Top Box
- DSL or Cable Modem
- PC/IA
- Auto PC Device
- TFT Monitor
- Battery-Powered Portable Applications
- Distributed Power Systems
Q & A
- What is the input voltage range of the LM3485?
The input voltage range of the LM3485 is from 4.5 V to 35 V.
- What is the adjustable output voltage range of the LM3485?
The output voltage can be adjusted from 1.242 V to VIN.
- What is the maximum operating frequency of the LM3485?
The maximum operating frequency of the LM3485 is greater than 1 MHz.
- Does the LM3485 require control-loop compensation?
No, the LM3485 does not require control-loop compensation due to its hysteretic control architecture.
- What type of protection does the LM3485 offer?
The LM3485 offers current limit protection by measuring the voltage across the RDS(ON) of the PFET.
- What is the thermal resistance of the LM3485 in the VSSOP package?
The junction-to-ambient thermal resistance of the LM3485 in the VSSOP package is 163.3 °C/W.
- What are some common applications of the LM3485?
Common applications include set-top boxes, DSL or cable modems, PC/IA devices, auto PC devices, TFT monitors, battery-powered portable applications, and distributed power systems.
- How does the LM3485 achieve high efficiency at light loads?
The LM3485 achieves high efficiency at light loads due to its hysteretic control architecture, which reduces the operating frequency at light loads, thus maintaining excellent efficiency.
- What is the package type and pin count of the LM3485?
The LM3485 comes in a VSSOP package with 8 pins.
- How is the output voltage programmed in the LM3485?
The output voltage can be easily programmed using two external resistors.
