EDNE December 2012 - (Page 24)

0.3V. Though the actual input voltage is about 0.5V, what appears at the boost input would be 0.2V. As a result, the SMP would not start at 0.5V input. The board designer can avoid this situation by using wider traces of shorter length, placing the components in a way that keeps the conduction paths short. Another design issue is the emissions that result from the switching current into the SMP. When the inductor stores charge, the input current is higher. In addition, this current switches between two extremes as the inductor stores and discharges power. SOC OR MICROCONTROLLER CHIP POWER 1.8V SMP 3.3V RF CHIP Figure 3 In this example of a controller and an RF chip for wireless communications, the RF chip needs 3.3V for its operation, whereas 1.8V is sufficient for the controller. the layout design of a low-input-voltage sMp circuit Must be done with extreMe care. Consider a scenario in which 0.5V is being boosted to about 3V; assume the load draws about 50 mA. The input current in this case for an ideal SMP would be 300 mA. If the converter is not ideal, this current will be even higher. If there are any long traces through which this current flows, electromagnetic emissions can result that affect the operation of nearby circuits. If there are any analog components nearby, for example, their performance might not be acceptable. To avoid this situation, isolate the switching path from the other sensitive components by using guard traces that are connected to ground. booSt-converter featureS The boost converter may also be used in any system that requires a higher operating voltage than the supply provides. One example would be driving a 5V LCD in a 3.3V system. Another example would be an application that uses a controller and an RF chip for wireless communication (Figure 3). The RF chip may require 3.3V for its operation, whereas 1.8V might be sufficient for the controller. In this scenario, an input-regulated voltage can power the controller; at the same time, the SMP available on the controller can boost the input voltage to 3.3V and supply the RF chip. The SMP on a controller thus can be used in applications that require multiple supplies. A number of manufacturers provide SOCs with on-chip SMPs that offer unique features. Cypress Semiconductor’s PSoC architecture, for example, has an SMP in addition to other resources, such as precision programmable analog and digital components. The boost converter on the SOC can be operated in either active or standby mode. Active mode is the normal mode of operation, wherein the boost regulator actively generates a regulated output voltage from the battery input. In standby mode, most boost functions are disabled to reduce the boost circuit’s power. The converter can be configured to provide low-power, low-current regulation in standby mode. An external, 32-kHz crystal can be used to generate inductor boost pulses on the rising and falling edges of the internal clock when the output voltage is less than the programmed value; this mode is called ATM (automatic thump mode). The boost typically draws 200 μA in active mode and 12 μA in standby mode. The switching frequency can be set to 100 kHz, 400 kHz, 2 MHz, or 32 kHz to optimize efficiency and component cost. The 100-kHz, 400-kHz, and 2-MHz switching frequencies are generated using oscillators internal to the boost-converter block. When the 32-kHz switching frequency is selected, the clock is derived from the 32-kHz external crystal oscillator. The 32-kHz external clock is primarily intended for boost standby mode. An on-chip SMP in microcontrollers and SOCs is helpful in powering low-power embedded applications. Improving a battery’s efficiency helps improve its endurance, resulting in fewer discarded batteries. SMPs also encourage designers to develop solar-cell-powered systems.EDN referenceS “AN2097: PSoC1 Switch Mode Pump Application Note,” Cypress Semiconductor Corp, 2012, www.cypress.com/?rID=2797. 2 “CY8C29466, CY8C29566, CY8C29666, CY8C29866: PSoC Data Sheet,” Cypress Semiconductor Corp, 2012, www.cypress.com/?rID=3334. 3 “PSoC 3: CY8C38 Family Data Sheet,” Cypress Semiconductor Corp, 2012, www.cypress.com/?rID=35178. 1 author’S biography Gautam Das G is an applications engineer at Cypress Semiconductor. He received his bachelor’s degree in engineering from RV College of Engineering (Bangalore, India). His interests include analog circuit design and embedded systems. 24 eDN europe | december 2012 www.edn-europe.com http://www.cypress.com/?rID=2797 http://www.cypress.com/?rID=3334 http://www.cypress.com/?rID=35178 http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE December 2012

Cover
Contents
Texas Instruments Europe
Microchip
Digi-Key
Masthead
EDN comment
Pulse
Digi-Key
Baker’s Best
Embedded World 2013
Test & Measurement World
Rohde & Schwarz
Digi-Key
Squeezing the most from battery cells with a switched-mode pump
Signal integrity
Processor architectures : one to rule them all ?
Digi-Key
Mechatronics in Design
Advances in wireless speaker performance and technology
Design Ideas
Teardown; the ultimate Consumer Product ?
Product roundup
Tales from the Cube

EDNE December 2012