AN10882 Dependency of BLF578 gate bias voltage on

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: salesaddresses@nxp.com
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: salesaddresses@nxp.com
Date of release: 17 December 2009
Document identifier: AN10882_1