NXP Semiconductors AN10714 Installation and operating instructions

AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
Rev. 01 — 26 January 2010 Application note
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Keywords BLF574, 600 MHz performance, high voltage LDMOS, amplifier
implementation, Class-B CW, FM band, pulsed power
Abstract This application note describes the design and the performance of the
BLF574 for Class-B CW and FM type applications in the 88 MHz to
108 MHz frequency range.

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 2 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
Revision history
Rev Date Description
01 20100126 Initial version

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 3 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
1. Introduction
The BLF574 is a new, 50 V, push-pull transistor using NXP Semiconductors’ 6th
generation of high voltage LDMOS technology. The two push-pull sections of the device
are completely independent of each other inside the package. The gates of the device are
internally protected by the integrated ElectroStatic Discharge (ESD) diode.
The device is unmatched and is designed for use in applications below 600 MHz where
very high power and efficiency are required. Typical applications are FM/VHF broadcast,
laser or Industrial Scientific and Medical (ISM) applications.
Great care has been taken during the design of the high voltage process to ensure that
the device achieves high ruggedness. This is a critical parameter for successful broadcast
operations. The device can withstand greater than a 10 : 1 VSWR for all phase angles at
full operating power.
Another design goal was to minimize the size of the application circuit. This is important in
that it allows amplifier designers to maximize the power in a given amplifier size. The
design highlighted in this application note achieves over 600 W in the 88 MHz to 108 MHz
band in a space smaller than 50.8 mm ×101.6 mm (2 ” ×4 ”). The circuit only needs to be
as wide as the transistor itself, enabling transistor mounting in the final amplifier to be as
close as physically possible while still providing adequate room for the circuit
implementation.
This application note describes the design and the performance of the BLF574 for
Class-B CW and FM type applications in the 88 MHz to 108 MHz frequency band.

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 4 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
2. Circuit diagrams and PCB layout
2.1 Circuit diagrams
Fig 1. BLF574 input circuit schematic; 88 MHz to 108 MHz
001aal30
4
R12
R7
D1
R8 R3
R9
R4
C4
R15 R14 R10
R1
R2 R5
R11
L22
C7 C6 C5
C9
Q2
C1
C27
R16
L10
L11
C26C25
C8
B1
L3
L4
L7
L6
L8
L24
L9
L5
L1
L2
T1
T2
C3
C2
A
C30
R13
Q3
C29C28
B
RF in
V bias in
Q1

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 5 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
Fig 2. BLF574 output circuit schematic; 88 MHz to 108 MHz
RF out
T3
T4 L25
L15
L14
L17
L19
L21
L16
L12
L13
B2
C24
C32
C31
C33
C34
L12
C21 C22 C23
C17 C18 C19 C20
L20
C14
C10
C15
C11
C16
C13
C12
001aal30
5
Q3
L23

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AN10714_1 © NXP B.V. 2010. All rights reserved. Application note Rev. 01 — 26 January 2010 6 of 21 NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
2.2 BLF574 PCB layout
The positions of C1, C19 and C23 are indicated but these capacitors are not connected.
Fig 3. BLF574 PCB layout
001aal30
6
BLF574
input-rev 3
30RF35
BLF574
output-rev 3
30RF35
C1
L3
L2
L1
L4
L7
L8
L9
L10
L12
L14
L13
L11
L24
L6
B
C3
C4
D1
C6
R8 C5
R15
Q2
R14
C9
B1
C25
C26
C8
C30
R13
R4
R1
R5
R2
R3
R7
Q1
A
C27
Q3
R16
T1
T2
L22 R9 C7
C24
C14
L19
L20
L21
C21
C22
C23
C17 C18 C19
L18
L15
L16
L17
L
25
C13
T4
C11
C16
C10
C15
C32
C33
C34
B2
T3
R10R12 C29
C28
R11
C31
C20
C2 C12
L23

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 7 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
2.3 Bill Of Materials
Table 1. Bill of materials for the BLF574 input and output circuits
PCB material: Taconic RF35; ε
r= 3.5; thickness 0.76 mm (30 mil). Figure 3 shows the BLF574 PCB layout.
Designator Description Part number Manufacturer
B1 63.5 mm (2.5 ”)/50 Ωsemirigid through
ferrite[1] ferrite: BN-61-202 Amidon
semirigid: 047-50 Micro-Coax
B2 coax cable; 124.5 mm (4.9 ”)/50 Ω;
ID = 3.5814 mm (0.141 ") UT-141C-Form-F Micro-Coax
C1 not connected - -
C2, C3 4700 pF ceramic chip capacitor ATC700B472KW50X American Technical Ceramics
C4, C7, C26, C29 1 μF ceramic chip capacitor GRM31MR71H105KA88L MuRata
C5, C6, C9 100 nF ceramic chip capacitor GRM21BR71H104KA01L MuRata
C8 620 pF ceramic chip capacitor ATC100B621JT100X American Technical Ceramics
C10, C11 390 pF ceramic chip capacitor ATC100B220GT500X American Technical Ceramics
C12, C13 180 pF ceramic chip capacitor ATC100B181JT200X American Technical Ceramics
C14 6.8 pF ceramic chip capacitor ATC100B6R8CT500X American Technical Ceramics
C15, C16 15 pF ceramic chip capacitor ATC100B150JT500X American Technical Ceramics
C17, C21, C31, C32 100 nF/250 V ceramic chip capacitor GRM32DR72E104KW01L MuRata
C18, C22, C33, C34 2.2 μF/100 V ceramic chip capacitor GRM32ER72A225KA35 MuRata
C19, C23 not connected - -
C20, C24 1000 μF, 100 V electrolytic capacitor EEV-TG1V102M Panasonic
C25, C28 10 nF/35 V ceramic chip capacitor GRM32ER7YA106KA12L MuRata
C27, C30 100 nF ceramic chip capacitor GRM31CR72E104KW03L MuRata
D1 LED APT2012CGCK KingBright
L1 21.7 mm ×1.75 mm (855 mil ×69 mil) - -
L2 9.2 mm ×1.65 mm (364 mil ×65 mil) - -
L3 9.9 mm ×1.75 mm (390 mil ×69 mil) - -
L4, L5 6.2 mm ×5.5 mm (243 mil ×218 mil) - -
L6, L7 [2] - -
L8, L9 5.2 mm ×5.54 mm (205 mil ×218 mil) - -
L10, L11 13.0 mm ×13.2 mm (511 mil ×520 mil) - -
L12, L13 8.8 mm ×13.2 mm (345 mil ×520 mil) - -
L14, L15 8.83 mm ×3.81 mm (348 mil ×150 mil) - -
L16, L17 [2] - -
L18, L23 3 turns 14 gauge wire;
ID = 7.9 mm (0.310 ”) - -
L19 21.2 mm ×1.75 mm (834 mil ×69 mil) - -
L20 9.5 mm ×1.82 mm (373 mil ×72 mil) - -
L21 13.99 mm ×1.7 mm (551 mil ×65 mil) - -
L22 ferroxcube bead 2743019447 Fair Rite
L24 50.8 mm (2 ”); 14 gauge wire;
ID = 15.5 mm (0.61 ”)[3] - -
L25 7.6 mm ×15.3 mm (299 mil ×604 mil) - -

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 8 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
[1] The semirigid cable length is defined in Figure 4.
[2] Contact your local NXP Semiconductors sales person for the artwork file containing the dimensions.
[3] N-male connector mounted as close to the package as possible.
Q1 7808 voltage regulator NJM#78L08UA-ND NJR
Q2 SMT 2222 NPN transistor PMBT2222 NXP Semiconductors
Q3 600 W LDMOST BLF574 NXP Semiconductors
R1 200 Ωpotentiometer 3214W-1-201E Bourns
R2, R3 432 Ωresistor CRCW0805432RFKEA Vishay Dale
R4 2 kΩresistor CRCW08052K00FKTA Vishay Dale
R5 75 Ωresistor CRCW080575R0FKTA Vishay Dale
R6 not connected - -
R7, R9 1.1 kΩresistor CRCW08051K10FKEA Vishay Dale
R10 11 kΩresistor CRCW080511K0FKEA Vishay Dale
R11 5.1 Ωresistor CRCW08055R1FKEA Vishay Dale
R12 499 Ω/0.25 W resistor CRCW2010499RFKEF Vishay Dale
R13, R16 9.1 Ωresistor CRCW08059R09FKEA Vishay Dale
R14 5.1 kΩresistor CRCW08055K10FKTA Vishay Dale
R15 910 Ωresistor CRCW0805909RFKTA Vishay Dale
T1, T2 63.5 mm (2.5 ”)/25 Ωsemirigid through
ferrite[1] ferrite: BN-61-202 Amidon
semirigid: 047-25 Micro-Coax
T3, T4 coax cable 86.36 mm (3.4 ”)/25 Ω;
ID = 2.18 mm (0.086 ") E22[1]STJ Thermax
Table 1. Bill of materials for the BLF574 input and output circuits …continued
PCB material: Taconic RF35; ε
r= 3.5; thickness 0.76 mm (30 mil). Figure 3 shows the BLF574 PCB layout.
Designator Description Part number Manufacturer
Fig 4. Cable length definition
001aak52
4
semirigid cable length

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 9 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
2.4 PCB form factor
Care has been taken to minimize board space for the design. Figure 5 shows how 600 W
can be generated in a space only as wide as the transistor itself.
3. Amplifier design
3.1 Mounting considerations
To ensure good thermal contact, a heatsink compound (such as Dow Corning 340) should
be used when mounting the BLF574 in the SOT539A package to the heatsink. Improved
thermal contact is obtainable when the devices are soldered on to the heatsink. This
lowers the junction temperature at high operating power and results in slightly better
performance.
When greasing the part down, care must be taken to ensure that the amount of grease is
kept to an absolute minimum. The NXP Semiconductors’ website can be consulted for
application notes on the recommended mounting procedure for this type of device or from
your local NXP salesperson.
3.2 Bias circuit
A temperature compensated bias circuit is used and comprises the following:
An 8 V voltage regulator (Q1) supplies the bias circuit. The temperature sensor (Q2) must
be mounted in good thermal contact with the device under test (Q3). The quiescent
current is set using a potentiometer (R1). The gate voltage correction is approximately
−4.8 mV/°C to −5.0 mV/°C. The VGS range is also reduced using a resistor (R2).
Fig 5. Photograph of the BLF574 circuit board
001aal30
7

AN10714_1 © NXP B.V. 2010. All rights reserved.
Application note Rev. 01 — 26 January 2010 10 of 21
NXP Semiconductors AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
The −2.2 mV/°C at its base is generated by Q2. This is then multiplied by the R14 : R15
ratio for a temperature slope (i.e. approximately −15 mV/°C). The multiplication function
provided by the transistor is the reason it is used rather than a diode. A portion of the
−15 mV/°C is applied to the potentiometer (R1).
The amount of temperature compensation is set by resistor R4. The ideal value of which
proved to be 2 kΩ. The values of R11 and R13 are not important for temperature
compensation. However, they are used for baseband stability and to improve IMD
asymmetry at lower power levels.
3.3 Amplifier alignment
There are several points in the circuit that allow performance parameters to be readily
traded off against one another. In general, the following areas of the circuit have the most
impact on the circuit operating frequency and PL(1dB) performance. The modification areas
are listed in order of sensitivity, with the most sensitive tuning elements listed first.
Effect of changing the output capacitors (C12 and C13):
•This is a key tuning point in the circuit. This point has the strongest influence on the
trade-off between efficiency and linearity.
Effect of the length of the output balun (B2):
•The frequency can be shifted by modifying this element. Typically, the longer the
balun, the more the response is shifted to lower frequencies. Conversely, a short
balun shifts the response to higher frequencies.
Effect of changing the output 4 : 1 transformers (T3 and T4):
•The frequency can be shifted by modifying these elements. In general, longer
transformers shift the whole response to a lower frequency. Shortening the
transformers shifts the response to higher frequencies. Changes in efficiency and
PL(1dB) is seen when the characteristic impedance of these transformers is changed.
Effect of changing the output capacitor (C14):
•Changing this output capacitor has an effect of tilting the response over the band. The
efficiency or PL(1dB) performance can be made more consistent over the band by
modifying C14.
Effect of adding capacitance off the drain (C10, C11, C15, and C16):
•A small adjustment in the trade-off between efficiency and PL(1dB) performance can be
made by changing these capacitors.