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LTC3529: Step-Up DC/DC Converter for USB OTG

by element14

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To introduce the LTC3529 step-up DC/DC converter for USB On-The-Go applications

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Welcome to the training module on Linear Technology LTC3529: Step-Up DC/DC Converter for USB OTG. This training module introduces the LTC3529 step-up DC/DC converter for USB On-The-Go applications.
The LTC3529 is a 1.5MHz, current mode, synchronous boost DC/DC converter with automatic overload fault detection. The USB-OTG specific protection circuit includes a fault flag and can be programmed to either latch-off or restart after a time-out duration when the bus is overloaded. The LTC3529’s internal 1.5A switches can deliver up to 500mA of output current to a fixed 5V output (from single cell Li-Ion). The LTC3529 is most similar to the LTC3528B as they share synchronous rectification, integrated output disconnect, V IN >V OUT regulation and a very compact footprint. However, the LTC3529 adds an automatic fault protection functionality needed for USB-OTG applications.
The LTC3529 is a 5V output, synchronous, fixed frequency step-up DC/DC converter optimized for USB On-The-Go OTG) hosting applications, such as personal media players, digital cameras and printers, smart phones, and digital broadcast tuners.
The LTC3529’s input voltage range of 1.8V to 5.25V make it ideal for Li-Ion/Polymer or multicell alkaline/NiCd/NiMH applications. Synchronous rectification enables efficiencies of up to 95% extending battery run-time in handheld applications. The combination of a 2mm x 3mm DFN-8 package and a constant switching frequency of 1.5MHz minimize both inductor and capacitor sizes, thereby providing a tiny solution footprint required in handheld applications. It uses internal switches with an R DS(ON) of only 90mOhm (N-Channel) and 120mOhm (P-Channel) to deliver efficiencies as high as 95%. The output disconnect feature allows the output to be completely disconnected in shutdown. It also limits the inrush of current during start-up, minimizing surge currents seen at the input supply rail. The LTC3529 will also regulate the output if input voltage exceeds the output voltage. Additional features include anti-ringing control, short-circuit protection, soft-start, short circuit latch-off and thermal protection.
The LTC3529 is most similar to the LTC3528B as they share synchronous rectification, integrated output disconnect, V IN >V OUT regulation and a very compact footprint. However, the LTC3529’s 1.8V to 5.25V input voltage range is targeted at dual cell alkaline and single cell Li-Ion applications whereas the LTC3528/B’s 0.7V start up voltage also targets single cell alkaline applications. Similarly, as the LTC3529 is targeted at USB applications, it uses a fixed 5V output in lieu of the LTC3528/B’s adjustable output. The LTC3529 does NOT use BurstMode operation making it closer to the LTC3528B and also has a slightly lower switch current rating (1.5A vs. 2A). However, the largest difference is the LTC3529’s automatic fault detection which protects USB-OTG devices from a shorted USB output. If the output is shorted, the LTC3529 will reach its current limit, if this lasts longer than 22ms, it will send up a fault flag and the device will shutdown. If the auto start option is enabled (via the RST pin) the device will automatically attempt to restart every 22ms until the short is removed. If the auto start option is not enabled, the IC will remain shutdown until being manually restarted by toggling the SHDN pin or cycling the input voltage. In general, if the application is a USB-OTG host, the LTC3529 will be the preferred device.
USB-OTG is an emerging sector of electronics that allows devices to be connected to each other via a USB2.0 cable, eliminating the need for a central host such as a PC. For example a printer could host a digital camera and the same camera could host a cell phone. Some applications can be both a host and a peripheral, while others are solely peripherals. These USB 2.0 connections generally have two functions, the first is to transmit data and the second is to provide power. The USB power standards are set at 5V with either a 100mA or 500mA continuous current rating. How does the USB-OTG requirements affect power ICs in these applications? First, the IC needs to protect the host from overloading and destroying the power IC/host in case the USB output is shorted; the most common reason for a short will be water in the USB port or cable end. This is precisely what the LTC3529’s automatic fault detection does. It can be programmed to restart after a short is removed or after the device’s power is toggled on/off. The other important requirement for USB power ICs is that they must be stable with a relatively low value 6.5 μF output capacitor to ensure that the data link ramps up in the required time frame.
The LTC3529 step-up DC/DC converter can achieve very high efficiency. The efficiency of it can reach as high as 95%.
The LTC3529 operates with an input voltage as low as 1.8V and features fixed-frequency current-mode PWM control for exceptional line and load regulation. Internal MOSFET switches with low RDS(ON) and low gate charge enable the device to maintain high efficiency over a wide range of load current. The LTC3529 provides soft-start by ramping the inductor current limit from zero to its peak value in approximately 2ms. The LTC3529 is shut down by pulling the SHDN pin below 0.35V, and activated by pulling the SHDN pin above 1V. To prevent the device from providing power to a shorted output, the switch current is monitored to detect an over-current condition. The anti-ringing circuit connects a resistor across the inductor to damp the ringing on SW in discontinuous conduction mode. If the die temperature reaches approximately 160 º C, the device enters thermal shutdown, and all switches are turned off.
The LTC3529 switches large currents at high frequencies. Special care should be given to the PCB layout to ensure stable, noise-free operation. The figure depicts the recommended PCB layout to be utilized for the LTC3529. Here also list a few key guidelines for the PCB layout.
Here is a reference design using Li-Ion Battery to 5V at 100mA or 500mA for USB OTG Host Supply.
Thank you for taking the time to view this presentation on “ LTC3529: Step-Up DC/DC Converter” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Linear Technology site – link shown – or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility.

LTC3529: Step-Up DC/DC Converter for USB OTG Presentation Transcript

LTC3529: Step-Up DC/DC Converter for USB OTG
- Source: LINEAR TECHNOLOGY
Introduction
- Purpose
- Outline
- Content
LTC3529: What is it?
- 1.5A, 1.5MHz Synchronous Boost Converter For USB-OTG Applications
Typical Market Applications
- Personal Media Players
- Digital Cameras and Printers
- Smart Phones
- Digital Broadcast Tuners
Key Features
- Compact Solution for 5V USB On-The-GO V BUS Power
- 5V at 500mA from Single Li-Ion Cell
- Automatic Fault Detection
- High Efficiency: Up to 95%
- V IN Range: 1.8V to 5.25V
- Fixed 5V Output
- Short Circuit Protection
- 1.5MHz Low Noise, Fixed Frequency PWM
- Inrush Current Limiting and Internal Soft-Start
- Output Disconnect
- <1μA Quiescent Current in Shutdown
- V IN > V OUT Operation
- 8-Lead, 2mm × 3mm DFN Package
LTC3529 Positioning Synchronous Buck Converters Linear Tech Linear Tech Linear Tech Part # LTC3529 LTC3528/B LTC3401 V IN Range (After Start-Up) 1.8V to 5.25V 0.5V to 5V 0.5V to 5V V OUT Range 5V-Fixed 1.6 to 5.25V 2.5V to 5.5V Automatic Fault Detection Yes No No Output Disconnect Yes Yes No Soft-Start Yes Yes No Efficiency ( I OUT =200mA, V IN =3.6V,V OUT =5V) 93% 92% 92% Switch Current 1.5A 1A 1A Frequency 1.5MHz 1MHz 300kHz to 3MHz V IN >V OUT Operation Yes Yes No Internal Compensation Yes Yes No Quiescent Current (uA) 500 µA 12 / 300 µA 38 / 440 ? A Shutdown Current < 1 µA < 1 µA < 1 ? A Inductor Value 2 . 2 µH 4 . 7 µH 4 . 7 µH C OUT Value (Ceramic) 6 . 5 µF 10 µF 22 µF Package (smallest) 2x3 DFN-8 2x3 DFN-8 MS10 Required to Meet USB Spec
Typical Application Schematic Figure 1. LTC3531 for Single Cell Li-Ion Input to 3.3V
LTC3529 Efficiency Curves
LTC3529 Operation
- PWM operation – fixed-frequency current –mode control at all load current.
- Soft-Start – ramping the inductor current limit from zero to its peak value in approximately 2ms
- Shutdown - pulling the SHDN pin below 0.35V
- Current Limit - shuts off the N-channel MOSFET switch when the current limit threshold is reached
- Fault Detection - prevents the device from providing power to a shorted output
- Anti-Ringing Control - damps the ringing on SW in discontinuous conduction mode
- Thermal Shutdown - If the die temperature reaches approximately 160 º C, the device enters thermal shutdown and all switches are turned off .
PCB Layout Guidelines
- All circulating current paths should be kept as short as possible.
- The PGND pin should be shorted directly to the exposed pad.
- All the external components and their connections should be placed over a complete ground plane.
- Use of multiple vias in the die attach pad will enhance the thermal environment of the converter
Reference Design
Additional Resource
- For ordering LTC3529, please click the part list or
- Call our sales hotline
- For additional inquires contact our technical service hotline
- For more product information go to

LTC3529: Step-Up DC/DC Converter for USB OTG

by element14

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LTC3529: Step-Up DC/DC Converter for USB OTG Presentation Transcript

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