AN10882 Dependency of BLF578 gate bias voltage on temperature Rev. 01 — 17 December 2009 Application note Document information Info Content Keywords BLF578, HV LDMOS Abstract This application note describes the dependency of the BLF578 transistor gate bias voltage on junction temperature AN10882 NXP Semiconductors Dependency of BLF578 gate bias voltage on temperature Revision history Rev Date Description 01 20091217 Initial version Contact information For more information, please visit: http://www.nxp.com For sales office addresses, please send an email to: [email protected] AN10882_1 Application note © NXP B.V. 2009. All rights reserved. Rev. 01 — 17 December 2009 2 of 6 AN10882 NXP Semiconductors Dependency of BLF578 gate bias voltage on temperature 1. Introduction The BLF578 is a 50 V push-pull transistor using NXP Semiconductor’s sixth generation of HV LDMOS technology. The BLF578 has a high degree of ruggedness, critical for successful broadcasting, due to the carefully designed high voltage fabrication process. Within the BLF578 package, the two push-pull modules are completely independent of each other and the gates are protected by the integrated ElectroStatic Discharge (ESD) diode. The BLF578 is unmatched and designed for use in applications where very high power and efficiency are required. At full operating power, the BLF578 can withstand a 13:1 VSWR for all phase angles. Typical uses are FM/VHF broadcasting, laser, and Industrial Scientific and Medical (ISM) applications. This application note describes the dependency of gate bias voltage on the BLF578 transistor junction temperature. This dependency can be used by a temperature compensated bias circuit to ensure that the quiescent drain current remains constant during RF operation. 2. Measurement results To determine the dependency of gate-bias voltage on temperature, the BLF578 case temperature (Tcase) was allowed to reach 70 °C and gradually water cooled to 5 °C. Over this temperature range the gate-source voltage (VGS) was adjusted to maintain a constant quiescent current (IDq) and the values of VGS and Tcase were recorded. The measurements were performed for IDq values of 0.2 A, 1 A and 2 A at a supply voltage (VDS) of 50 V as shown in Figure 1. 001aal116 2.0 VGS (V) 1.8 (1) 1.6 (2) (3) 1.4 1.2 0 20 40 60 80 100 Tcase (°C) (1) IDq = 2 A. (2) IDq = 1 A. (3) IDq = 0.2 A. Fig 1. Gate-source voltage as a function of case temperature AN10882_1 Application note © NXP B.V. 2009. All rights reserved. Rev. 01 — 17 December 2009 3 of 6 AN10882 NXP Semiconductors Dependency of BLF578 gate bias voltage on temperature The values of the three quiescent currents used in the measurements were chosen to represent typical quiescent currents found in NXP Semiconductor applications. 001aal117 Fig 2. BLF578 junction temperature measured by infrared camera The case temperature (Tcase) was measured below the flange as shown in Figure 3. (1) 1 mm (2) 001aal118 (1) Tcase. (2) Heatsink temperature (Th). Fig 3. BLF578 temperature measurement points 3. Abbreviations Table 1. Abbreviations Acronym Description HV High Voltage LDMOS Laterally Diffused Metal Oxide Semiconductor VSWR Voltage Standing Wave Ratio AN10882_1 Application note © NXP B.V. 2009. All rights reserved. Rev. 01 — 17 December 2009 4 of 6 AN10882 NXP Semiconductors Dependency of BLF578 gate bias voltage on temperature 4. Legal information 4.1 Definitions Draft — The document is a draft version only. The content is still under internal review and subject to formal approval, which may result in modifications or additions. NXP Semiconductors does not give any representations or warranties as to the accuracy or completeness of information included herein and shall have no liability for the consequences of use of such information. 4.2 Suitability for use — NXP Semiconductors products are not designed, authorized or warranted to be suitable for use in medical, military, aircraft, space or life support equipment, nor in applications where failure or malfunction of an NXP Semiconductors product can reasonably be expected to result in personal injury, death or severe property or environmental damage. NXP Semiconductors accepts no liability for inclusion and/or use of NXP Semiconductors products in such equipment or applications and therefore such inclusion and/or use is at the customer’s own risk. Applications — Applications that are described herein for any of these products are for illustrative purposes only. NXP Semiconductors makes no representation or warranty that such applications will be suitable for the specified use without further testing or modification. Disclaimers General — Information in this document is believed to be accurate and reliable. However, NXP Semiconductors does not give any representations or warranties, expressed or implied, as to the accuracy or completeness of such information and shall have no liability for the consequences of use of such information. Right to make changes — NXP Semiconductors reserves the right to make changes to information published in this document, including without limitation specifications and product descriptions, at any time and without notice. This document supersedes and replaces all information supplied prior to the publication hereof. Export control — This document as well as the item(s) described herein may be subject to export control regulations. Export might require a prior authorization from national authorities. 4.3 Trademarks Notice: All referenced brands, product names, service names and trademarks are the property of their respective owners. AN10882_1 Application note © NXP B.V. 2009. All rights reserved. Rev. 01 — 17 December 2009 5 of 6 AN10882 NXP Semiconductors Dependency of BLF578 gate bias voltage on temperature 5. Contents 1 2 3 4 4.1 4.2 4.3 5 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement results . . . . . . . . . . . . . . . . . . . . . Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . Legal information. . . . . . . . . . . . . . . . . . . . . . . . Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trademarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 4 5 5 5 5 6 Please be aware that important notices concerning this document and the product(s) described herein, have been included in section ‘Legal information’. © NXP B.V. 2009. All rights reserved. For more information, please visit: http://www.nxp.com For sales office addresses, please send an email to: [email protected] Date of release: 17 December 2009 Document identifier: AN10882_1