Application Notes

APPLICATION NOTE
Video Amplifier Board with
TDA4885 and CR6927
AN97039
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Purchase of Philips I 2C components conveys
a license under the I 2C patent to use the components in the I 2C system, provided the
system conforms to the I 2C specifications
defined by Philips.
© Philips Electronics N.V. 1997
All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.
The information presented in this document does not form part of any quotation or contract, is believed to be
accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any
consequence of its use. Publication thereof does not convey nor imply any license under patent- or other industrial
or intellectual property rights.
2
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPLICATION NOTE
Video Amplifier Board with
TDA4885 and CR6927
AN97039
Author(s):
P. Rombout
Philips Semiconductors Systems Laboratory Eindhoven,
The Netherlands.
Keywords
Video Controller
Active Load Output Amplifier
AC-coupling
Black Level Restoration
I2C-bus Control
Power Dissipation
Number of pages: 45
Date: 97-07-15
3
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Summary
This report describes the video amplifier board with 150 MHz video controller TDA4885 and 140 MHz hybrid
active load output amplifier CR6927. The printed circuit board is designed to drive both 15" and 17" colour
monitors with 100 MHz bandwidth. AC-coupling to the cathodes is used, which enables a low supply voltage.
Together with the choice for the active load module with low static power dissipation, this results an economical
board with a small heatsink. This AC-coupling does need additional circuitry, such as a buffer, negative supply
for the CR6927 inputs as well as DC-restoration at the cathodes. With the included I2C-software, functions such
as contrast, brightness, OSD contrast, individual gain and individual black-level control are available. The board
is capable of receiving signals for beam current limiting and gain modulation. A system description with highlights
of TDA4885 and CR6927 is given. Block diagram and schematics of the system is explained. Also, measuring
data and various design hints are included. For a description of an DC-coupled application, see Application Note
AN96074: ’Video Amplifier Board with TDA4885 and CR1296’.
4
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
CONTENTS
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1
Video Controller TDA4885 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1
Pinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.2
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.3
Signal Input Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.4
Electronic Potentiometer Stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.5
Output Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.6
Pedestal Blanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.7
Output Clamping, Feedback References and DAC Outputs . . . . . . . . . . . . . . .
2.1.8
Horizontal Clamping and Vertical Blanking Pulses . . . . . . . . . . . . . . . . . . . . . .
2.1.9
Horizontal Flyback Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.10
OSD and OSD Contrast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.11
Beam Current Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.12
Gain Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.13
I2C-bus Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2
Output Amplifier CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1
Pinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2
Internal Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3
OSD Generator PCB8517 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.1
Pinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
10
11
12
12
12
13
13
13
13
13
15
15
15
16
16
16
17
17
18
3. SYSTEM SCHEMATICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1
Application Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.1
TDA4885 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.2
CR6927 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.3
PCB8517 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.4
Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.5
DC-Restoration Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.6
Heater and grid voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
Printed Circuit Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3
Heatsink CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
19
19
19
20
20
20
20
21
21
4. MEASURING DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1
Video Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5. DESIGN HINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1
Ground Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2
Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3
Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4
Black Level Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5
Speed-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.6
Accu Colour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
25
25
25
25
26
26
27
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
5.7
5.8
Application Note
AN97039
Gain Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Smearing Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
APPENDIX 1: I2C CONTROL SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
APPENDIX 2a: INTERNAL BLOCK DIAGRAM TDA4885 (left side) . . . . . . . . . . . . . . . . . . . . . . . . 31
APPENDIX 2b: INTERNAL BLOCK DIAGRAM TDA4885 (right side) . . . . . . . . . . . . . . . . . . . . . . . 32
APPENDIX 3a: SCHEMATICS SYSTEM (left side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
APPENDIX 3b: SCHEMATICS SYSTEM (right side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
APPENDIX 4: MONITOR ALIGNMENT PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
APPENDIX 5: CALCULATIONS FLASH RESISTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
APPENDIX 6a: LAY-OUT PRINTED CIRCUIT BOARD (component side) . . . . . . . . . . . . . . . . . . . 37
APPENDIX 6b: LAY-OUT PRINTED CIRCUIT BOARD (solder side) . . . . . . . . . . . . . . . . . . . . . . . 38
APPENDIX 7: COMPONENTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
APPENDIX 8: POWER DISSIPATION CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
LIST OF FIGURES
Fig.1 Block Diagram Video Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.2 Signal Output TDA4885 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.3 Timing diagram clamping and blanking pin 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.4 Output Signal Modulated Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.5 Internal Circuit Video Hybrid CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.6 Thermal Resistances Video Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.7 Construction Heatsink on CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.8 Cathode Voltage Video Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.10 Internal Block Diagram TDA4885 (left side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.11 Internal Block Diagram TDA4885 (right side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.12 System Schematics (left side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.13 System Schematics (right side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.14 Monitor Alignment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.15 PCB Lay-out and Component Placement Component Side . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig.16 PCB Lay-out and Component Placement Solder Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
10
14
14
15
17
21
22
23
31
32
33
34
35
37
38
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
LIST OF TABLES
TABLE 1: Pin Description TDA4885 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TABLE 2: Pin Description CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TABLE 3: Pin Description PCB8517 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TABLE 4: Temperature CR6927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
11
16
18
24
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
8
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
1.
Application Note
AN97039
INTRODUCTION
This report describes the video amplifier demo board with video controller TDA4885 and output amplifier
CR6927. It is designed to drive both 15" and 17" colour monitors with 100 MHz. A separate On Screen Display
(OSD) generator is present on the board. AC-coupling to the cathodes is used, which means a low output
amplifier supply voltage and therefore, a low power dissipation. A DC-restore circuit is implemented with a simple
diode clamp and an amplifier with only four transistors for three channels. The active load amplifier CR6927 has
a low static power dissipation, but requires a buffer between TDA4885 and its inputs in order to yield a 100MHz
bandwidth. Also, a negative supply voltage is needed to drive the CR6927 inputs.
9
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.
Application Note
AN97039
SYSTEM DESCRIPTION
The video amplifier system consists of: pre-amplifier, control functions, OSD generator, I2C-bus and output
amplifier, as shown in figure 1.
gain modulation
R G B
GAIN MODULATION
CONTROL
PCB8517
high speed
enable/data/clock
focus
H/Vsync grids
OSD
GENERATOR
OSD
CONTROL
BUFFER(3x)
R G B PREAMPLIFIER
R G B
CR6927
AC-COUPLING(3x)
R G B OUTPUT
AMPLIFIER
tube
feedback
black level control
DC-RESTORE
CIRCUIT(3x)
I2 C
CONTROL
TDA4885
VIDEO BOARD
I2 C
data/clock
Fig.1 Block Diagram Video Board
Video controller IC TDA4885 and output amplifier hybrid CR6927 are the core of the video board, the rest of the
circuitry serves as drive or interface for these devices. The two following subparagraphs will be devoted to the
TDA4885 and CR6927. OSD generator PCB8517 will be described in the third subparagraph.
2.1
Video Controller TDA4885
The TDA4885 is a 150 MHz RGB pre-amplifier for colour monitor systems with On Screen Display (OSD) and
I2C-bus. It can drive discrete stages as well as hybrid video modules. The pre-amplifier is used with positive
feedback from output (or buffer output) for AC-coupling with fixed black-level output. Black-level restore at the
cathodes is possible with the aid of three external DAC reference voltages. I2C-bus control software is being
delivered on diskette with the video board, appendix 1 shows the software menu with the options mentioned
above.
10
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.1.1
Application Note
AN97039
Pinning
Pin description of the TDA4885 is given in table 1. For more characteristics, the TDA4885 data sheet (Ref. 1) can
be used for reference.
TABLE 1: Pin Description TDA4885
SYMBOL PIN
PARAMETERS
DESCRIPTION
FBL
1
1.1 V ≤ threshold ≤ 1.7 V
Fast blanking for OSD insertion
OSD1
2
-6 ns ≤ delay after FBL ≤ +6 ns,
trise/tfall ≤ 7 ns
OSD input channel 1 (green)
OSD2
3
"
OSD input channel 2 (red)
OSD3
4
"
OSD input channel 3 (blue)
CLI
5
1.2 V ≤ threshold ≤ 1.6 V (blanking)
2.6 V ≤ threshold ≤ 3.5 V (clamping)
Vi1
6
0.7 V referred to black, 4.0 V during input Signal input channel 1 (green)
clamping
Vp
7
8.0 V typ., 7.6 V min, 8.8 V max.
Supply voltage
Vi2
8
See pin 6
Signal input channel 2 (red)
GND
9
Vi3
10
See pin 6
Signal input channel 3 (blue)
HFB
11
2.6 V ≤ threshold ≤ 3.5 V (clamping)
1.0 V ≤ threshold ≤ 1.8 V (blanking)
Horizontal flyback input for output clamping and
blanking
GM1
12
open-circuit: 2.0 V;
Gain modulation input channel 1 (green)
ground: no gain modulation (max. gain);
modulated gain: 1 - 3 V.
See figure 4.
GM2
13
See pin 12
Gain modulation input channel 2 (red)
GM3
14
See pin 12
Gain modulation input channel 3 (blue)
SDA
15
0 V ≤ VLOW ≤ 1.5 V, 3.0 V ≤ VHIGH ≤ 5.0 V
I2C-bus serial data input
SCL
16
Clock ≤ 100 kHz
I2C-bus serial clock input
LIM
17
4.5 V: start contrast/OSD contrast
reduction, 2.0: max. reduction (-25 dB),
5.0 V open-circuit
Beam current limiting
GND3
18
Vp3
19
8.0 V typ., 7.6 V min., 8.8 V max.
Supply channel 3
Vo3
20
2.8 V (nom. contrast, max. gain) ≤ Vo3 ≤
4.5 V (max. contrast, max. gain)
0.5 V ≤ black level ≤ 2.5 V
Signal output channel 3
Actual black level depends on
external feedback network
FB3
21
4.0 V ≤ FB3 ≤ 5.8 V negative feedback,
0.7 V positive feedback
Feedback input channel 3
Vertical blanking input;
clamping input
Ground
Ground channel 3
11
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
TABLE 1: Pin Description TDA4885
SYMBOL PIN
PARAMETERS
DESCRIPTION
REF3
22
4.0 V ≤ REF3 ≤ 5.8 V
Reference voltage channel 3
GND2
23
Vp2
24
See pin 19
Supply channel 2
Vo2
25
See pin 20
Signal output channel 2
FB2
26
See pin 21
Feedback input channel 2
REF2
27
See pin 22
Reference voltage channel 2
GND1
28
Vp1
29
See pin 19
Supply channel 1
Vo1
30
See pin 20
Signal output channel 1
FB1
31
See pin 21
Feedback voltage channel 1
REF1
32
See pin 22
Reference channel 1
2.1.2
Ground channel 2
Ground channel 1
Block Diagram
In appendix 2, the internal block diagram of the TDA4885 is depicted. Diagram sections and their functioning are
listed in the paragraphs below.
2.1.3
Signal Input Stage
The RGB signal inputs (0.7 V) must be capacitively coupled (10 nF recommended) to the TDA4885 from a lowohmic source (75 Ω recommended). These AC-coupling capacitors allow level shift and clamping of the input
signals to reference black level. Missing input clamping pulses will result in black output signals because internal
leakage currents discharge the coupling capacitor. A clipping circuit cuts all signal parts below black level. Video
signals can be enabled or disabled by I2C-bus.
2.1.4
Electronic Potentiometer Stages
Three electronic potentiometer stages are present as 6-bit, I2C-driven, DACs with the following functions:
CONTRAST CONTROL
This DAC simultaneously adjusts all three input signals related to reference black level with a range of 25 dB.
BRIGHTNESS CONTROL
Video black level can be shifted in relation to reference black level for all three channels simultaneously. A
negative setting will shift dark signal parts in ultra black and a positive setting will change background from black
to grey.
12
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
GAIN CONTROL
Gain is an individually controlled white point adjustment, that controls video signals related to reference black
level over a range of 7 dB. It affects the complete grey scale. It is used to compensate for the sensitivity of the
R/G/B guns and phosphors (the three colours need a different drive for a white picture). With gain control, Accu
Colour can be implemented.
2.1.5
Output Stage
The output RGB signals are amplified to 2.8 Vpp (12 dB) at nominal contrast and maximum gain. At maximum
contrast and gain settings, output voltage is 4.5 Vpp (16 dB). Reference black level is controllable from
0.5 to 2.5 V. Total output voltage range is limited from 0.5 to Vp-2.0 V.
2.1.6
Pedestal Blanking
Output signals can be blanked to ultra black level by setting pedestal blanking (bit PEDST=1), which adds 0.45 V
during clamping. This is necessary for AC-coupling applications with a passive clamp diode circuit as DCrestoration to prevent unwanted clamping during video overshoots. With pedestal blanking, the clamping pulse
surely is the highest voltage, and black level is restored during clamping only.
2.1.7
Output Clamping, Feedback References and DAC Outputs
Output clamping stabilises the reference black level at the output. Without clamping pulses, output signals will go
to switch-off voltage because the integrated storage capacitors will discharge. In case of AC-coupling, the buffer
output (emitter) voltage is fed back to the IC. Without the buffer, the TDA4885 output is directly connected to its
feedback pin. During output clamping, this feedback voltage is compared to 0.7 V. Output control range during
clamping is 0.5 V to 2.5 V. Figure 2 depicts output signal with variable gain, contrast and brightness.
2.1.8
Horizontal Clamping and Vertical Blanking Pulses
Threshold for input line clamping is 3 V and for vertical blanking 1.4 V. Vertical blanking is only enabled when the
input signal is present for a certain minimum time between 1.4 V and 3 V. During vertical blanking, signal and
brightness blanking are activated and possible pedestal blanking. Input signals have to be at black level during
the input clamping pulse. Figure 3 gives a timing diagram for clamping/blanking pulses.
2.1.9
Horizontal Flyback Pulses
Horizontal flyback pulse HFB has two levels: 1.4 V at which signal blanking, brightness blanking and possible
pedestal blanking are activated and 3 V at which additionally the output clamped feedback loop is activated.
13
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
max.
nom.
min.
blanking/output clamping pin 11
gain max.
contrast nom.
brightness var.
video black level
reference black level
blanking level
colour
signal
gain max.
brightness max.
contrast var.
video black level
reference black level
blanking level
video
signal
brightness max.
contrast nom.
gain var.
video black level
reference black level
blanking level
Fig.2 Signal Output TDA4885
trise/fall:
<=75 ns/V
>280 ns/V
3.0 V
input clamping threshold
1.4 V
input blanking threshold
input pin 5
input clamping
blanking
tl
tt
tl
tl: time leading edge
tt: time trailing edge
Fig.3 Timing diagram clamping and blanking pin 5
14
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.1.10
Application Note
AN97039
OSD and OSD Contrast
If fast blanking input at pin FBL rises above its 1.4 V threshold, video input signals are blanked and OSD signals
enabled. Amplification of inserted signals OSD1 to -3 can be controlled by a 4-bit I2C-driven DAC ’OSD contrast’
with a range of 12 dB. OSD signals track with brightness and gain control as normal signals, but is independend
of video contrast. It is possible to enable/disable OSD signals by I2C-bus.
2.1.11
Beam Current Limiting
Beam current limiting by means of contrast reduction is possible with an external voltage at pin LIM. Maximum
overall voltage gain of contrast and OSD contrast control can be reduced by 26 dB (4.5 V: start of reduction,
2.0 V: maximum reduction).
2.1.12
Gain Modulation
Gain modulation is possible in order to achieve brightness uniformity over the screen by applying appropriate
waveforms to the input pins GM1, GM2 and GM3.
Open-circuit pins are at 2.0 V and yield a gain reduction of 20%. A symmetrical gain modulation is achieved by a
signal input of 1.0 to 3.0 V. This will modulate the open-circuit gain with -18% to +18%. If this feature is not used,
the pins should be grounded for maximum voltage gain. Figure 4 clarifies the effect of the gain modulation input
range.
Gain Modulation input:
nom.
max.
mod.
GND: gain +20%
1V: gain +18%
open (2V): gain nom.=0%
3V: gain -18%
output signal
Fig.4 Output Signal Modulated Gain
15
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.1.13
Application Note
AN97039
I2C-bus Control
An I2C-bus receiver is present for the following functions:
- Contrast control with 6-bit DAC (25 dB);
- Brightness control with 6-bit DAC (10-30% of nominal signal amplitude);
- OSD contrast control with 4-bit DAC (12 dB);
- Gain adjustment with 6-bit DAC for each channel (7 dB);
- Black level adjustment with 8-bit DAC for each channel;
- Control register for:
- feedback polarity
- RGB video on/off
- OSD on/off
- pedestal blanking on/off.
Registers are set to logic ’0’ after power-up and internal power-on reset of I2C-bus.
2.2
Output Amplifier CR6927
The video output amplification is achieved by hybrid module CR6927. This is a three channel (class AB active
load) amplifier with a small-signal bandwidth of 140 MHz and an open loop voltage gain of 180. A feedback
resistor Rfb is applied internally, which means the closed loop gain can adjusted by the input resistor Rin (see
figure 5).
2.2.1
Pinning
Table 2 gives a pin description of the CR6927, more characteristics can be found in its data sheet (Ref. 2).
TABLE 2: Pin Description CR6927
SYMBOL PIN
PARAMETERS
DESCRIPTION
Vs1
1
75 V - 90 V max.
Signal Supply channel 1 (blue)
Vi1
2
1.5 V typ.
Signal Input channel 1
GND
3
Vo1
4
½Vs1 typ.
Signal Output channel 1
Vs2
5
See pin 1
Signal Supply channel 2 (red)
Vi2
6
See pin 2
Signal Input channel 2
GND
7
Vo2
8
See pin 4
Signal Output channel 2
Vs3
9
See pin 1
Signal Supply channel 3 (green)
Vi3
10
See pin 2
Signal Input channel 3
GND
11
Vo3
12
Ground
Ground
Ground
See pin 4
Signal Output channel 3
16
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.2.2
Application Note
AN97039
Internal Circuit
The simplified internal circuit of one channel of the module is depicted in figure 5.
RFB
VS
RE_T2
R3
T3
T2
RBUF3
R2
R4
OUT
CK
IN
RBUF4
T1
RIN
R1
T4
RE_T1
GND
Fig.5 Internal Circuit Video Hybrid CR6927
The closed loop gain A is determined by Rin (for instance 326Û of this application):
Equ. 1
2.3
OSD Generator PCB8517
The PCB8517 is a stand-alone OSD generator, controlled by the microcontroller on the deflection board via a
three-wire high-speed serial interface. Horizontal and vertical position on screen, as well as character height,
colour and font can be programmed. The on-chip PLL oscillator adjust character size to the current graphic
mode. Additional information is specified in its data sheet (Ref. 3).
17
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
2.3.1
Application Note
AN97039
Pinning
Pinning of the PCB8517 is shown in table 3 below.
TABLE 3: Pin Description PCB8517
SYMBOL PIN
PARAMETERS
DESCRIPTION
GNDA
1
Analog Ground
VCO
2
Voltage Controlled Oscillator
BIAS
3
Bias Current Internal Oscillator
VsA
4
HS
5
Horizontal Sync Pulse
ENN
6
Serial Interface Enable, active low
SDI
7
Serial Interface Data
SCK
8
Serial Interface Clock
VsD
9
VS
10
Vertical Sync Pulse
HTONE
11
Halftone, not used in this application
FB
12
Fast Blanking
B
13
Blue Channel Output
G
14
Green Channel Output
R
15
Red Channel Output
GNDD
16
Digital Ground
4.75 V min, 5.0 V typ., 5.25 V max.
Analog Supply
See pin 4
Digital Supply
18
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
3.
Application Note
AN97039
SYSTEM SCHEMATICS
This paragraph will explain the depicted schematics of the video board. The two main building blocks of the
board are the TDA4885 and CR6927 with peripheral components that will be described first. Supply will be
treated in more detail in paragraph 5.2 on design hints. PCB lay-out will be explained and finally power and
heatsink calculations for the CR6927 are given.
3.1
Application Circuit
Schematics of the circuit around the TDA4885 and CR6927 is depicted in appendix 3. The video board also
interconnects the horizontal and vertical sync pulses from monitor input to deflection board and signals like
heater, Vg1 etc. from deflection board to picture tube. The monitor alignment procedure is included (adjusting
black-level, white point etc.) in appendix 4.
3.1.1
TDA4885 Application
* OSD inputs: generated by the separate OSD-generator PCB8517. These inputs are coupled via a 100 Ω
resistor to PCB8517.
* Clamping and blanking inputs, connected via 100 Ω to CON2. These signals are generated on the deflection
board.
* RGB-inputs: these signals are 0-0.7 V and connected via a 75 Ω cable, which means a 75 Ω terminator must
be present at the input on the video board. A 10 nF capacitor with a 33 Ω series resistor connects the
incoming signal to the input pins.
* Supply voltage 8 V from voltage stabilizer uA7808 (IC3), decoupled locally with a chip capacitor.
* Gain modulation inputs, connected via 100 Ω to connector CON3. If this feature is unused, the pins can
grounded.
* SDA/SCL I2C-bus inputs, generated by I2C-controller on deflection board. Pull-up resistors are present on
deflection board. Signals come in via connector CON1 and 220 Ω series resistors.
* Beam Current Limiter (BCL), generated on deflection board from CON2 via 100 Ω. This signal must force the
open-pin voltage of 5 V down to a range of 4.5 to 2.0 V when beam current must be limited. A 10 nF capacitor
is used to filter possible noise that might cause interference. A pull-up resistor ensures a voltage greater than
4.5 V in case beam current limiting must not be activated.
* Channel outputs: coupled to the CR6927 via a buffer (BFG35). All channels have separate ground and supply
voltage.
* Feedback from emitter of BFG35 buffer. The TDA4885 is set to positive feedback (AC-coupling) and feedback
black level during the clamp pulse is controlled at 0.7 V.
* External feedback reference voltages, used for the DC-restoration circuit in AC-coupling applications.
3.1.2
CR6927 Application
* RGB channel inputs, require a voltage swing of about 3-4 Vpp (dependent on closed loop gain) around 1.5 V,
connected through Rin, that will determine the closed loop gain (see equation 1). In order to shift the input
signals to the levels, delivered by the pre-amp, pull-down resistors R*08 haven been added.
19
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
* Output pins, connected via coupling capacitor and a flash resistor to the cathodes. A clamping diode pulls the
cathode voltage to a DC-restore value every horizontal flyback. This diode also leads possible flashes on the
cathodes away from the video amplifier’s outputs. The diode (BAV21) must be able to withstand the flash
current that is limited by the flash resistor (47 Ω, for calculations see appendix 5).
* Supply voltage (78 V) from deflection board and ground for each channel, decoupled locally by a chip
capacitor.
3.1.3
PCB8517
* High speed serial bus with enable, clock and data line, driven by the microcontroller on deflection board via
100Ω. Pull-up resistors (4k7) are also applied.
* H/V sync pulse inputs, connected via 100Ω to the H/V connectors.
* Phase Locked Loop (PLL) filter input and BIAS input for the Voltage Controlled Oscillator.
* 5 V analog and digital supply voltage and ground, separately decoupled.
* RGB and Fast Blanking (FB) outputs, connected via 100Ω to TDA4885 OSD inputs.
3.1.4
Buffer
A buffer transistor (BFG35) is used to increase the sink and source current for the output stage. The feedback
pin of the TDA4885 must be connected to the emitter of this emitter follower in order to minimize smearing. Since
the buffer is connected to a negative supply, the feedback pin must be set to > 300mV during start-up to avoid
latch-up. This is done by connecting a divider to the feedback pin of the TDA4885 with a pull-up resistor to +8 V
and a resistor to the emitter of the buffer.
3.1.5
DC-Restoration Circuit
The DC-restoration circuit must be a temperature independent DC-amplifier. This amplifier is fed by the
TDA4885 reference voltages (range 4.0-5.8 V). These voltages are amplified to the desired black-levels at the
cathodes (with a range of the maximum 17" tube cut-off voltage difference of 25 V). This is implemented by
creating a temperature-dependent voltage at the emitter of the three amplifiers. The DC-amplifiers are closed
loop connected transistors in order to achieve a stabile DC output. With only four transistors, it is possible to
achieve a three-channel temperature-stabile accurate DC-amplifier.
3.1.6
Heater and grid voltages
Voltages for heater and grids 1 and 2 of the CRT are generated on the deflection board. The grid voltages Vg1
and Vg2 are coupled to the CRT by a 2.7 kΩ series resistor and a 1 nF high-voltage capacitor is connected to
ground. Heater voltage is via a 1 Ω resistor and a 10 µH inductor connected to the heater, heater ground is
connected by a 10 µH series inductor. Both heater and heater ground are decoupled by a 1.5 nF capacitor to
ground. Spikes are caused by fast voltage swings on the cathodes and are, without decoupling capacitors,
picked up by the heater and grids. The inductors and 2.7 kΩ resistors ensure that this is the route of least
impedance.
20
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Note: The Vg1 voltage, applied to pin 8 of connector 2 must be approximately -50 V, with a superimposed
vertical blanking pulse of at least 10 V.
3.2
Printed Circuit Board
In designing the video Printed Circuit Board (PCB), care has to be taken that all connections are as short as
possible and connectors have to be placed close to the ICs’ input pins. All channel inputs of the TDA4885 are
placed at one side (pins 1-16) and outputs at the other (pins 17-32), which makes layout design easy: the inputs
enter on one side of the board, followed by TDA4885 that drives CR6927 and at the other side the CRT-socket.
The choice was made for a double-sided board to avoid oscillations. With a double-sided board, one side is used
as ground plane. This enables short ground returns, reducing EMI. The use of SMD components in combination
with leaded components ensures the shortest connection possible between inputs, ICs and outputs. Especially
the local decoupling of supply voltages with capacitors 10-100 nF must be close to the corresponding pins, which
means it is best to use SMD components. Lay-out of the board is depicted in appendix 6, followed by the
components list in appendix 7.
3.3
Heatsink CR6927
The video hybrid module dissipates too much power to conduct to free air. This means a heatsink must be fixed
to its mounting base. Figure 6 shows the thermal resistances and corresponding local temperatures.
Pmax
CR6927
junction
xK\W
RTH_J_MB
Tmax
=
100
C
mounting
base
0.2K\W
RTH_MB_H
heatsink
2.2K\W
RTH_MB_A
65
C
ambient(monitor)
Fig.6 Thermal Resistances Video Module
The maximum power dissipated by the CR6927 is 16.8 Watts (appendix 8 includes calculations that lead to this
value). The thermal resistance between mounting base and heatsink is assumed 0.2 °C\W. It is specified that the
operating temperature of the CR6927 mounting base is ≤ 100 °C, in order to keep the junction temperatures of
the internal transistors within safe limits. The required thermal resistance is specified in equation 2.
21
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Equ. 2
The mounting base is first fixed to an aluminium block, that is connected to the print. The actual heatsink is
mounted to this block, as shown in the cross-section of figure 7. The heat must be conducted well from the block
to the heatsink, if necessary with heat-conducting paste.
heatsink
alumimium block
mounting base
junction
print
CR6927
Fig.7 Construction Heatsink on CR6927
The area of the heatsink (2mm thick aluminium) is defined by equation 3.
Equ. 3
In which:
k = 1.5*10-3 W\Kcm2, for aluminium heatsink 2mm thickness with about the calculated area
A = heatsink area in cm2
Rtherm = thermal resistance from heatsink to ambient
With the previously calculated values: A = 1\(1.5*10-3 * 1.9) = 350 cm2, the size of the heatsink is chosen at
13 * 23 =299 cm2. This is smaller than calculated, but the worst case situation on which this calculation is based
is not likely to occur. If necessary, a larger heatsink can be chosen.
22
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
4.
4.1
Application Note
AN97039
MEASURING DATA
Video Performance
Video performance is specified by rise/fall times and DC-voltages at the cathodes. Measurements have been
carried out in an actual monitor (15" Mk 2, see Ref. 4). Load capacitance is defined by:
Equ. 4
The (reference) black-levels on the cathodes can be adjusted between 50 V and 75 V (measured) with the three
DAC registers of the TDA4885. This range is sufficient to compensate for the difference of cut-off voltages of one
tube.
Figure 8 shows the cathode waveform of a 50 Vpp voltage swing at nominal brightness (an Astro video generator
is used as a signal source).
Fig.8 Cathode Voltage Video Board
Rise and fall times (time between 10% and 90% of voltage swing) at the cathodes are measured with a Tektronix
TDS520 500MHz oscilloscope using a high-frequency calibrated Tektronix P5100 100x 2.4 pF probe. The
corresponding input signal of the TDA4885 is generated by a PM585 pulse generator with rise/fall times smaller
than 1 ns. These conditions yield a rise time of 4.4 ns and a fall time of 3.5 ns, at a voltage swing from 15 to 65 V.
Overshoot of the white to black transition is below 5%, overshoot from black to white is more than 10%.
Bandwidth of this system is calculated by B = 0.35\tfall. Fall time (black to white transition) is the most critical
transition time, because it is best visible on screen. Overall system bandwidth is:
Bsystem = 0.35\(3.5*10-9) = 100 MHz. The board can be used for pixel rates up to 200 MHz.
23
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
4.2
Application Note
AN97039
Temperature
Measurements have proved that most power is dissipated in CR6927 when displaying a 100 MHz pixel on/off
picture. Temperature measurements have been carried out with the heatsink construction and size as described
in paragraph 3.3. The first row of table 4 shows data with a pixel on/off picture at maximum contrast
(Vpp = 50.4 V) and nominal brightness. The ∆T of this measurement remains the same at a higher ambient
temperature. The second row of this table shows the mounting base temperature of CR6927 at the maximum
ambient temperature of 65°C, which is the internal monitor temperature.
TABLE 4: Temperature CR6927
Tambient [°C]
Tmounting base [°C]
∆T [°C]
Measured
23.5
57.4
35.7
Calculated
65.0
98.7
35.7
It appears from table 4 that the heatsink is sufficiently large for this worst case situation when placed inside a
monitor. It should be noted that it takes the heatsink about half an hour to heat up. This means this worst case
temperature of 98.7 °C is not likely to occur, because an on/off picture is hardly ever displayed for half an hour.
24
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
5.
Application Note
AN97039
DESIGN HINTS
When developing a printed circuit board for the TDA4885 and/or the CR6927, certain design rules and hints
have to be taken into account. The most critical items are highlighted in the following subparagraphs.
5.1
Ground Routing
A printed circuit video amplifier board that has to operate at frequencies higher than 40 MHz, a double-sided
board is needed. The copper in this second side should be used as much as possible as a ground plane. If only
ground tracks are used, signal loops will be created. Through these loops, ground currents flow that can easily
cause oscillations. In case of a ground plane on one board side, there are hardly any loops which means the
chance on ground currents to cause oscillations is limited. The plane also shields the board from electromagnetic radiation from and to the environment (EMI). This plane, however, does create parasitic capacitance to
the signal paths. In order to avoid parasitic capacitance to high-frequency video signal paths, the plane area
directly near these signal paths should be cleared.
5.2
Supply
Low voltage supplies (+11 V and -18 V) must enter the board via a series resistor (about 1-10 Ω) and be
controlled by a voltage stabilizer or zener diode. The stabiliser should be decoupled by a capacitor (100-330 nF)
on both input and output. Output must be stabilised by an elcap of 10 - 68 µF. From this point, the supply voltage
must be led to the corresponding voltage pins via a 1-10 Ω series resistor. These supply pins must be locally
decoupled by a (chip) capacitor of about 100 nF, placed as close as possible to the pin itself.
For the high voltage supply of 78 V of the CR6927, similar rules must be followed, only for the series resistors, it
is recommended to use 1 Ω. This is necessary in order to reduce supply variations by high peak currents. This is
not necessary for the +185 V supply, it enters the board via 100Ω, because high peak currents do not occur.
5.3
Buffer
A buffer between pre- and output amplifier is applied, because the maximum sink and source current of the
TDA4885 outputs are 12 and 15 mA respectively. The CR6927 needs a higher current in order to achieve its
maximum rise and fall times. The necessary current can be calculated by equation 5, based on the fall time
(video black to white transition), which is best visible on screen.
Equ. 5
More information on the internal capacitance (2.4 pF) is given in appendix 8.
A fall time of 3.5 ns (measured from 10% to 90% of the voltage swing) and a maximum voltage swing of 50 Vpp
(40 V 10%-90%), this yields:
The buffer is an emitter follower (npn transistor BFG35) with an emitter resistor to -8 V supply, that will determine
the sink and source current. During white video level of the TDA4885 output, the buffer current must be at least
26.3 mA. Video white level for a 50 Vpp output swing is:
Vclamp+Vpedestal+Vsignal = 0.7+0.45+4.0 = 5.15 V. The emitter resistor value has to be:
25
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Equ. 7
This minimal value could be experimentally increased (current decreased) until a noticeably slower fall time is
reached.
If it is chosen not to implement a buffer in trade of slower transition times, this feedback pin can be connected
directly to the TDA4885 output pin.
Note: If the emitter of this buffer is fed back to the TDA4885 and is connected to a negative supply (via a
resistor), this may cause a latch-up situation. Therefore, the feedback pin must be set to > 300mV during startup. This is achieved by a divider from +8 V (resistors R*24/R*11) to the buffer’s emitter, which sets the feedback
pin to about 1 V during start-up.
5.4
Black Level Control
Black level (at the cathodes) control is achieved by a clamp diode DC-restore circuit. The clamp diode restores
the cathode voltage to a defined black level during the clamp pulse. The defined black level is created by Three
DC-amplifiers, driven by the external reference voltages Vref of the TDA4885. A range of 50 V-75 V is chosen,
because the lowest level may not be negative during video, but the level should also be as low as possible, in
order to allow Vg1 to be as little negative as possible. The three DC-amplifiers (T*02, where ’*’ stands for channel
1, 2 or 3) receive a temperature-compensated voltage at their emitters. The transistors are connected in a
feedback circuit, in which ∆Vref is approximately amplified by Rfb\Rin = R*20\R*21 = 91k\5k6 = 16 times. The
output voltage range must cover the maximum cut-off voltage difference of the cathodes, which is 25 V for 17"
tubes. Cathode voltage will be 8-10 V lower, because the emitter voltage of T*02 is set at 8-10 V. The resistors
R*19 at the collector are applied to limit the collector-emitter voltage of T*02.
5.5
Speed-up
In order to achieve the best possible rise and fall times, a speed-up circuit has to be applied over Rin of the
CR6927. The input circuit consists of two series RC-combinations. The value of Rin is divided in a large and small
part. Speed-up capacitors C*03 and C*04 speed up the slope of the CR6927 output signal by increasing the
high-frequency gain. Start values for C*03/C*04 can be calculated by first measuring the CR6927 output time
constant (τo ≈ 20-25 ns), this is done by only connecting a resistor as input network. The time constant, created
by C*03 * R*09 and C*04 * R*10 must then be made equal to this value (where τo2 ≈ {(C*03*R*09)2 +
(C*04*R*10)2}).
Mostly, the created time constant(s) must be decreased in order to limit overshoot. The optimized values for this
application are:
- R*09/C*03 = 270E/68pF;
- R*10/C*04 = 56E/82pF.
Note: The calculations above are just a guideline and optimal values are obtained experimentally.
26
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
5.6
Application Note
AN97039
Accu Colour
With Accu Colour, white colour temperature is adjustable. This colour temperature is adjustable by the gain
setting of the three R/G/B channels. The TDA4885 has individual gain control with a range of 7 dB. This is
needed for three functions:
1- Absolute sensitivity channels: proportion beam current that is necessary for the separate R/G/B guns in
order to achieve white with a certain colour temperature.
2- Spread sensitivity channels: spread on the absolute sensitivity mentioned above.
3- Accu Colour.
The first function could be implemented in hardware by applying different input resistors at the input pins of the
CR6927 three colour channels. This enables an individually adjustable gain. If the gain modulation pins are not
used, gain adjustment can be applied at these pins (see paragraph 5.6 here below).
The second function of gain adjustment of the TDA4885 is the compensation for the spread on channel
sensitivity. This function needs 3 dB at maximum.
The third function is Accu Colour and for this, the TDA4885 leaves a 4 dB control range. This range will be
sufficient for adjusting colour temperature from, for instance, 3500 K to 7000 K or 5000 K to 10,000 K.
5.7
Gain Modulation
Some picture tubes have a relatively large decrease of light output towards the edges. By applying a dynamic
waveform to the gain modulation inputs (pin 12, 13 and 14 of TDA4885), this light output decrease can be
compensated. In a simple application, a parabolic waveform of horizontal frequency can be applied to the three
pins simultaneously. For this, the HFOCUS signal from deflection controller TDA4855 is suitable. Only the
left/right loss on the display is then compensated. In a high performance application, top/bottom losses can also
be compensated by applying three separately adjustable signals from an X/Y wave form generator or a parabola
generator, such as deflection controller TDA4854.
If brightness uniformity is not implemented, the gain modulation pins can be used for gain adjustment. This can
be achieved by either a DC-potentiometer or an external DAC (for instance from Pulse Width Modulation output
of µC). In this way, the gain adjustment DAC’s of the TDA4885 are free for an enlarged Accu Colour user range.
5.8
Smearing Compensation
If the video board is applied without any compensation networks, it shows some visual smearing. Therefore, two
smearing compensation networks are implemented on the board:
- An RC-series network, parallel to the input network of the CR6927, for the compensation of the TDA4885
smearing. This is a smearing that shows an undershoot (D≈7-8%) with time constant
τs,1≈50 ns. The value of compensation resistor R*23 is calculated in equation 8.
27
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Equ. 8
The value for C*11 must be: τs,1\R*23 = 50ns\4k3 = 12pF.
- An RC-series network, from output to input of the CR6927 in order to compensate its own smearing. This is an
overshoot smearing (D≈2%) with time constant τs,2≈15µs. The value for compensation resistor R*14 must be
calculated by equation 9:
Equ. 9
The RC-combination must match the smearing time constant:
C*07 = τs,2\R*14 = 15µs\220k = 68pF.
Note: These compensation values are start values, the final values must be obtained experimentally.
28
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
6.
Application Note
AN97039
REFERENCES
Ref. 1:
Ref. 2:
Ref. 3:
Ref. 4:
Data sheet TDA4885, issued 1996 March 13.
Data sheet CR6927, issued 1996 February 29.
Data sheet PCB8517, issued 1995 March 7.
’PCALE 15" Autosync Monitor Mk2 circuit description’ by Han Misdom. Report number AN95086.0,
issued 1995 September 5.
Ref. 5: Data sheet 17" tube, data handbook DC01: ’Colour TV Picture Tubes and Assemblies’, issued
1994 October.
29
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
30
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 1: I2C CONTROL SOFTWARE
Note: Contrary to the example above, feedback polarity should be set ’Positive’ for the application, described in
this report.
31
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 2a: INTERNAL BLOCK DIAGRAM TDA4885 (left side)
SDA SCL
LIM
16
15 16
data
Vi1 6
Vi1
Vi1
6
6
6 BIT
DAC
I 2 C-BUS
LIMITING
OSD
BLANKING
REGISTER
INPUT
CLAMPING
BLANKING
CLIPPING
CONTRAST
INPUT
CLAMPING
BLANKING
CLIPPING
CONTRAST
INPUT
CLAMPING
BLANKING
CLIPPING
CONTRAST
6 BIT
DAC
4 BIT
DAC
FPOL
DISV
DISO
PEDST
BLANKING
OSD
CONTRAST
BRIGHTNESS
OSD
CONTRAST
BRIGHTNESS
OSD
CONTRAST
BRIGHTNESS
blanking
input clamping
DISO
INPUT CLAMPING
VERTICAL BLANKING
OSD INPUT
fast blanking
TDA4885
1
FBL
2
3
OSD1
OSD2
4
OSD3
Fig.10 Internal Block Diagram TDA4885 (left side)
32
5
CLI
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 2b: INTERNAL BLOCK DIAGRAM TDA4885 (right side)
GM1 GM2 GM3
12 13 14
data
MODULATION
6 BIT
DAC
6 BIT
DAC
6 BIT
DAC
8 BIT
DAC
8 BIT
DAC
8 BIT
DAC
CHANNEL 3
REFERENCE
22 REF3
CHANNEL 2
REFERENCE
27 REF2
CHANNEL 1
REFERENCE
32 REF1
FPOL
POLARITY
SWITCH
GAIN
PEDESTAL
BLANKING
PEDESTAL
BLANKING
30
Vo1
24
Vp2
25
Vo2
23 GND2
26 FB2
GAIN
PEDESTAL
BLANKING
DISV
Vp1
28 GND1
31 FB1
GAIN
KING
29
19
Vp3
20
Vo3
18 GND3
21 FB3
BLANKING
OUTPUT CLAMPING
SUPPLY
11
7
9
HFB
Vp
GND
Fig.11 Internal Block Diagram TDA4885 (right side)
33
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 3a: SCHEMATICS SYSTEM (left side)
IC3 PCF8517
1
C1
16
R1
2 VCO
R 15
C2 10k R4
3 PLL
G 14
5k6
4 VDD
B 13
R5
5 HS
FB 12
5k6
100n
R3
R2
1M
100n
HS
IC1
100E
4k7 R36
4k7
4k7
R35
R34
R6 100E
R7 100E
CON1
SCK
OSD
GEN
8
SDI
R8 100E
6 ENN
VS
8 SCK
SCK
10
n.u.
R11
R12 1
100E
100E
C3
100n
ENN
11
7 SDI
R9
10E
9
VS
C4
100n 10E
I2 C
5V
R201 3
100E
Input2
Red
R13
Gnd
SCL
Input1
Green
R301 4
100E
5V
+5V
5
Vref
32
Feedback
31
R102
10n
33E
R103
75E
L3
10u
R14
10E
C201
10n
Channel1
Green
Input3
Blue
Output
Vsupply
29
Clamping
R202
78V
R302
33E
R104
Channel2
8
Vsupply
Input2
Red
9
Ground
10
Input3
Blue
11
* If GainMod
not used
Vref
27
*
12
0E R125
R204 13
0E R225
R304 14
100E
*
R224 -8V
Feedback
R212
7k5
10E
C205
100n
T201
BFG35
26
R223
4k3
R209
270E
C203
Channel2
Red
Output
25 R205
10E
R206
24
10E
8V
10E
C202
100n
Ground
23
Vref
22
Feedback
78V
C212 100n -8V
R312
10E
C305
100n
R324 7k5
Blanking
68p
R226
R323
4k3
T301
BFG35
Vref3
R309
R311
21
270E
C303
1k
100E
4
28
1k
100E
Channel3
Ground
R211
33E
R15
Channel1
68p
R126
10E
C112 100n
R207
470E
10n
R303
75E
*
8V
Input1
Green
100E
1
270E
C103
R107
470E
R106
C5
100n
C301
Ground
4k3
R109
30 R105
10E
10E
C102
100n
Vsupply
Gain Modulation
CON3
R123
1k
R203
75E
CON4
Blue
Input
10E
C105
100n
T101
BFG35
Vref2
7
8V
CON5
Red
Input
6
7k5
R111
OSD
C101
CON6
Green
Input
R112
8V
100E
1
Vref1
R124
R101 2
100E
R10
Gnd
SDA
TDA4885
Fast
Blanking
Gain Mod2
Red
Channel3
Blue
Output
Vsupply
20 R305
10E
19
SDA
R17
SCL
Ground
18
Beam Current
Limiter
17
I 2C
220E
R19
33k
68p
10E
78V
C312 100n -8V
R306
Gain Mod3
Blue
0E R325
R16
15
220E
16
R307
470E
R326
Gain Mod1
Green
10E
C302
100n
8V
1
R20
1E
C6
330n
63V
R21
1E
C16
10n
R18
100E
PR37981 Video Output Amplifier with TDA4885 and CR6927
Fig.12 System Schematics (left side)
34
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 3b: SCHEMATICS SYSTEM (right side)
R33
185V
11V
10E
R30
150k
C22 100n
T1
BC546B
IC2 CR6927
185V
C21
100n
R31
270E
R32
390E
8V
R116
1M
C109
Out
12
8V
R117
R114
R123
C111
4k3
R109
12p
R110
270E
C103
56E
C104
68p
82p
R115
1u
*
11 Gnd
200k
10
56p
C107
In
47E
D101
BAV21
100V
185V
C108
R118
62k
*
C110
R119
8k2
R108 1k5
9 78V Supply
200k
C207
*
Vref2
R208 1k5
78V Supply
1E
R312
5
C206 100n
100V
C305
Out
R323
C311
R314
R309
12p
R310
200k
270E
C303
56E
C304
68p
82p
R315
*
Gnd
C307
2
In
1u 100V
*
R318
62k
* optional
smearing
compensation
R308 1k5
R313
78V
C308
56p
R320
91k
R321
C306 100n
100V
Vref3
5V
uA7805
C7
2
100n
63V
1
uA7908
3
330n
63V
100n
63V
185V
R24
C11
33u
16V
C12
C20
10u
250V
100E
HS
78V
-8V
C13
100n
63V
8V
C10
2
T302
BC546B
C14
33u
16V
CON7
C15
R23
1E
VS
10u
100V
CON8
VSync
Input
R25 *
2k
330n
63V
1
14
CON2
BCL
1E
uA7808
10u
100V
8k2
2
R22 1E
3
1
C23 1n5
IC6
C8
33u
16V
IC5
C9
1n5
C17
47E
D301
BAV21
5k6
R322
3
1
C6
330n
63V
CON10
Aquadag
CON9
Vg2
C310
R319
8k2
1 78V Supply
1E
IC4
1n
2kV
1n
1kV
C18
R27
2k7
R29
1E
R316
1M
R317
C309
L2
10u
R28
2k7
4
4k3
3
C19
L1
10u
Fig.13 System Schematics (right side)
35
V-Sync
8V
C210
10u
100V
Aquadag
R213
78V
R219
8k2
R220 91k
T202
R221
BC546B
5k6
R222
8k2
M41EER
H-Sync
82p
56p
In
R218
62k
8
11
Vg1
68p
6
C208
6
47E
D201
BAV21
Ground
56E
C204
100V
Vff
270E
C203
1u
-18V
Gnd
7
Vff Gnd
12p
R210
R209
C209
*
Blanking
4k3
R216
1M
R217
R215
+185V
R214
C211
R223
R121
8k2
R122
8
+11V
8V
5k6
Out
100n
100V
10u
100V
T102
BC546B
Clamping
C106
R120 91k
+78V
78V
R212
10E
C205
Vref1
R113
1E
HSync
Input
R26 *
2k
* optional
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 4: MONITOR ALIGNMENT PROCEDURE
The cut-off voltage of the three R/G/B guns is different and the monitor must be aligned to compensate for this
voltage difference. Most of the following alignment procedure can be done by the TDA4885 software, except
Vg2. It is specified for a video board with AC-coupling to the cathodes. Figure 15 clarifies what the several
adjustments do to the cathode voltages.
- Set Vg2 to minimum, so that the three CRT cut-off levels are too low;
- Set the three black level DAC’s at maximum with positive feedback and with pedestal blanking (DAC=FF,
FPOL=1, PEDST=1). Check: Vcath ≈ 75 V.
- Set Contrast and Brightness to nominal values (Contrast: 26hex, Brightness: 10hex);
- Apply video signal test pattern and disable video (DISV=1). The output will be at reference black;
- Increase Vg2 slowly until one colour becomes just visible;
- Decrease cathode voltage of remaining colours by decreasing the corresponding black level DAC until these
colours also become just visible;
- Enable video (DISV=0);
- Adjust the three gain DAC’s until the desired white point (colour temperature) luminance is obtained.
75 V
one colour
visible
black level
decrease
all colours
visible
Vg2 increase
cathode
voltages
enable
video
GND
Fig.14 Monitor Alignment.
36
gain
adjustment
desired
white
point
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 5: CALCULATIONS FLASH RESISTOR
Purpose of the flash resistor from coupling capacitor to cathode is to limit flash diode current when a flash occurs
without limiting the video bandwidth of the system. Maximum non-repetitive diode current (BAV21) is 1 A for a
pulse ≤ 1 s and 5 A for a pulse ≤ 1 µs. If a flash occurs, it is led away from the video stage by the spark-gap and
flash diode to the DC-amplifier elcap. The RC-filter that is formed by the flash resistor and the load capacitance
(tube) is the limiting factor. Assuming a video bandwidth of 100 MHz, the cross-over frequency of the RC-filter
must by larger than 300 MHz. The influence of the RC-filter is then limited to 5%. Load capacitance is about 9 pF
(see equation 4), which yields a maximum flash resistor value of:
Equ. 10
A flashover consists of two phases:
- Before ignition of the spark-gap, a voltage of 2 kV is present for a time < 50 ns. The maximum flash resistor
value of 60 Ω limits the diode current to 2 kV\60 Ω ≈ 30 A. This is clearly more then the specified maximum of
5 A. In practice, the inductance of wires and print tracks limits the diode current to less than 30 A and the
BAV21 can withstand this very short pulse.
- After ignition of the spark-gap, a voltage of 150 V is present for a time < 1 µs. Now, a current from the voltage
of 150 V - 50 V (minimum elcap voltage) = 100 V must be limited to ≤ 5 A. This means the flash resistor must
have a minimum value of 100 \ 5 = 20 Ω. A value of 47 Ω is chosen (safety margin).
37
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 6a: LAY-OUT PRINTED CIRCUIT BOARD (component side)
Aquadag
CON10
PR37982
27-03-97
Video Output Amplifier with TDA4885 and CR6927
VG2
CON9
R27
L1
L2
C19
T102
R317
C18
C23
C17
R29
D301
R313
R318
R221
R218
T302
R213
C209
R113
R32
R33
C20
C109
T202
R219
C310
R220
R118
+
+ C309
+
+
R30
R31
R320
R319
R321
+
IC2
C15
R23
R316
+
T1
R22
+
C110
R119
+
D201
C210
R24
R121
R120
R217
R216
R116
D101
+185V
-18V
Aquadag
V-Sync
H-Sync
Ground
VG1
Vff Gnd
Vff
Blank
Clamp
+11V
+78V
BCL
R117
R28
R21
+
IC5
C11
R312
R112
R107
C14
IC6
CON3
R306
R305
R205
Gnd
G
R
B
R13
R8
R7
IC1
R6
R12
R17
R16
R202 C301
R302
C201
C101
R301
R102
R201
R101
R5
R11
R204
R104
R203
R15
CON4
CON5
CON6
CON7
B
R
G
H
V
* Optional
R303
R103
R26
CON8
R25
CON1
*
+--IIC--+
R304
R10
*
+--OSD--+
R9
Fig.15 PCB Lay-out and Component Placement Component Side
38
Gain Modulation
R226
R106
R14
R105
L3
IC3
+
R326
R206
IC4
C8
R18
R3
SCK
SDI
ENN
Gnd
SDA
+5V
Gnd
SCL
R307
+
R212
R207
CON2
R20
R126
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 6b: LAY-OUT PRINTED CIRCUIT BOARD (solder side)
C22
R214
R109
C10 C9
R108
C6
C212
R123 C111
C211
C106
C104
R110
C105
C12
C13
C112
C7
T101
R124
R223
C21
C107 R114
C103
C203
R209
R111
C1
R211
R309
C108 R115
R210 R208
R224
T201
R324
C312
C305
R311
C303
T301
C311 R323
C304 R310
C205 R308
C206
C204
R314
C306
C307
C208 R215
C207
C308 R315
R1
R4 C2
C102
C3
R2
R122
C5
R325
C4
R225
R34 R35 R36
C202
R222
R322
C302
C16
R19
R125
Fig.16 PCB Lay-out and Component Placement Solder Side
39
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 7: COMPONENTS LIST
Nbr.
Value/Range Type
12NC/info
--------------------------------------------------------------------------------------------------------R117 47E AB
AB6E
R217 47E AB
AB6E
R317 47E AB
AB6E
R27
2k7 AB
AB6E
R28
2k7 AB
AB6E
C108 *
C0805
Not placed
C208 *
C0805
Not placed
C308 *
C0805
Not placed
C111 12p
C0805
2222-861-12129
C211 12p
C0805
2222-861-12129
C311 12p
C0805
2222-861-12129
C107 56p
C0805
2222-861-12569
C207 56p
C0805
2222-861-12569
C307 56p
C0805
2222-861-12569
C103 68p
C0805
2222-861-12689
C203 68p
C0805
2222-861-12689
C303 68p
C0805
2222-861-12689
C104 82p
C0805
2222-861-12829
C204 82p
C0805
2222-861-12829
C304 82p
C0805
2222-861-12829
C16
10n
C0805
2222-590-16627
C1
100n
C0805
2222-910-16649
C2
100n
C0805
2222-910-16649
C3
100n
C0805
2222-910-16649
C4
100n
C0805
2222-910-16649
C5
100n
C0805
2222-910-16649
C7
100n
C0805
2222-910-16649
C10
100n
C0805
2222-910-16649
C13
100n
C0805
2222-910-16649
C21
100n
C0805
2222-910-16649
C22
100n
C0805
2222-910-16649
C102 100n
C0805
2222-910-16649
C105 100n
C0805
2222-910-16649
C112 100n
C0805
2222-910-16649
C202 100n
C0805
2222-910-16649
C205 100n
C0805
2222-910-16649
C212 100n
C0805
2222-910-16649
C302 100n
C0805
2222-910-16649
C305 100n
C0805
2222-910-16649
C312 100n
C0805
2222-910-16649
C6
330n
C0805
2222-910-16656
C9
330n
C0805
2222-910-16656
C12
330n
C0805
2222-910-16656
40
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Nbr.
Value/Range Type
12NC/info
--------------------------------------------------------------------------------------------------------C106 100n 100V
C1812
2222-614-16649
C206 100n 100V
C1812
2222-614-16649
C306 100n 100V
C1812
2222-614-16649
C101 10n
C2E
2222-370-41103
C201 10n
C2E
2222-370-41103
C301 10n
C2E
2222-370-41103
C18
1n 1kV
C3EE4
C19
1n 2kV
C3EE4
C17
1n5
CC2E
2222-630-03152
C23
1n5
CC2E
2222-630-03152
CON4 CoaxH 75E
COAXCONH
CON5 CoaxH 75E
COAXCONH
CON6 CoaxH 75E
COAXCONH
CON7 CoaxH 75E
COAXCONH
CON8 CoaxH 75E
COAXCONH
CON2 Stoko14
CON14
CON3 Stoko4
CON4
CON1 Stoko8
CON8
*
HOSIDEN213
CRT_DAF
IC3
PCF8517
DIL16
9352-996-00112
D101 BAV21
DO35
9331-892-10153
D201 BAV21
DO35
9331-892-10153
D301 BAV21
DO35
9331-892-10153
C15
10u 100V
E1E6
2222-300-39109
C110 10u 100V
E1E6
2222-300-39109
C210 10u 100V
E1E6
2222-300-39109
C310 10u 100V
E1E6
2222-300-39109
C20
10u 250V
E2E10
2222-044-63109
C109 1u 100V
E2E5
2222-037-59108
C209 1u 100V
E2E5
2222-037-59108
C309 1u 100V
E2E5
2222-037-59108
C8
68u 16V
E2E5
2222-030-35689
C11
68u 16V
E2E5
2222-030-35689
C14
68u 16V
E2E5
2222-030-35689
R115 *
R0805
Not Placed
R215 *
R0805
Not Placed
R315 *
R0805
Not Placed
R125 0E
R0805
Not Placed
R225 0E
R0805
Not Placed
R325 0E
R0805
Not Placed
R110 56E
R0805
2322-730-**569
R210 56E
R0805
2322-730-**569
R310 56E
R0805
2322-730-**569
R109 270E
R0805
2322-730-**271
R209 270E
R0805
2322-730-**271
41
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Nbr.
Value/Range Type
12NC/info
--------------------------------------------------------------------------------------------------------R309 270E
R0805
2322-730-**271
R111 1k
R0805
2322-730-**102
R211 1k
R0805
2322-730-**102
R311 1k
R0805
2322-730-**102
R308 1k2
R0805
2322-730-**122
R108 1k5
R0805
2322-730-**152
R208 1k5
R0805
2322-730-**152
R223 4k3
R0805
2322-730-**432
R123 4k3
R0805
2322-730-**432
R323 4k3
R0805
2322-730-**432
R34
4k7
R0805
2322-730-**472
R35
4k7
R0805
2322-730-**472
R36
4k7
R0805
2322-730-**472
R1
5k6
R0805
2322-730-**562
R4
5k6
R0805
2322-730-**562
R124 7k5
R0805
2322-730-**752
R224 7k5
R0805
2322-730-**752
R324 7k5
R0805
2322-730-**752
R122 8k2
R0805
2322-730-**822
R222 8k2
R0805
2322-730-**822
R322 8k2
R0805
2322-730-**822
R19
33k
R0805
2322-730-**333
R114 200k
R0805
2322-730-**204
R214 200k
R0805
2322-730-**204
R314 200k
R0805
2322-730-**204
R2
1M
R0805
2322-730-**105
IC1
TDA4885
SDIL32
9350-308-00112
R21
1E
SFR16
2322-180-**108
R29
1E
SFR16
2322-180-**108
R113 1E
SFR16
2322-180-**108
R213 1E
SFR16
2322-180-**108
R313 1E
SFR16
2322-180-**108
R9
10E
SFR16
2322-180-**109
R14
10E
SFR16
2322-180-**109
R33
10E
SFR16
2322-180-**109
R106 10E
SFR16
2322-180-**109
R112 10E
SFR16
2322-180-**109
R126 10E
SFR16
2322-180-**109
R206 10E
SFR16
2322-180-**109
R212 10E
SFR16
2322-180-**109
R305 10E
SFR16
2322-180-**109
R312 10E
SFR16
2322-180-**109
R102 33E
SFR16
2322-180-**339
R202 33E
SFR16
2322-180-**339
R302 33E
SFR16
2322-180-**339
42
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Nbr.
Value/Range Type
12NC/info
--------------------------------------------------------------------------------------------------------R103 75E
SFR16
2322-180-**759
R203 75E
SFR16
2322-180-**759
R303 75E
SFR16
2322-180-**759
R6
100E
SFR16
2322-180-**101
R7
100E
SFR16
2322-180-**101
R8
100E
SFR16
2322-180-**101
R11
100E
SFR16
2322-180-**101
R15
100E
SFR16
2322-180-**101
R101 100E
SFR16
2322-180-**101
R104 100E
SFR16
2322-180-**101
R201 100E
SFR16
2322-180-**101
R204 100E
SFR16
2322-180-**101
R301 100E
SFR16
2322-180-**101
R304 100E
SFR16
2322-180-**101
R16
220E
SFR16
2322-180-**221
R17
220E
SFR16
2322-180-**221
R31
270E
SFR16
2322-180-**271
R32
390E
SFR16
2322-180-**391
R107 470E
SFR16
2322-180-**471
R207 470E
SFR16
2322-180-**471
R307 470E
SFR16
2322-180-**471
R25
2k
SFR16
2322-180-**202 Not placed
R26
2k
SFR16
2322-180-**202 Not placed
R121 5k6
SFR16
2322-180-**562
R221 5k6
SFR16
2322-180-**562
R321 5k6
SFR16
2322-180-**562
R218 62k
SFR16
2322-180-**623
R318 62k
SFR16
2322-180-**623
R30
150k
SFR16
2322-180-**154
R116 1M
SFR16
2322-180-**105
R10
10E
SFR16_2E
2322-180-**109
R226 10E
SFR16_2E
2322-180-**109
R306 10E
SFR16_2E
2322-180-**109
R326 10E
SFR16_2E
2322-180-**109
R13
100E
SFR16_2E
2322-180-**101
R18
100E
SFR16_2E
2322-180-**101
R119 8k2
SFR16_2E
2322-180-**822
R219 8k2
SFR16_2E
2322-180-**822
R319 8k2
SFR16_2E
2322-180-**822
R120 91k
SFR16_2E
2322-180-**913
R220 91k
SFR16_2E
2322-180-**913
R320 91k
SFR16_2E
2322-180-**913
R20
1E
SFR16_4E
2322-180-**108
R22
1E
SFR16_4E
2322-180-**108
R105 10E
SFR16_4E
2322-180-**109
43
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
Nbr.
Value/Range Type
12NC/info
--------------------------------------------------------------------------------------------------------R205 10E
SFR16_4E
2322-180-**109
R12
100E
SFR16_4E
2322-180-**101
R5
100E
SFR16_4E
2322-180-**101
R3
10k
SFR16_4E
2322-180-**103
R118 62k
SFR16_4E
2322-180-**623
R216 1M
SFR16_4E
2322-180-**105
R316 1M
SFR16_4E
2322-180-**105
R23
1E
SFR25
2322-181-**108
R24
100E
SFR25
2322-181-**101
T101 BFG35
SOT223
9339-199-10115
T201 BFG35
SOT223
9339-199-10115
T301 BFG35
SOT223
9339-199-10115
IC2
CR6927
SOT347
9340-400-20127
L1
10u
SPOEL2E
L2
10u
SPOEL2E
L3
10u
SPOEL2E
IC4
uA7805
TO220
IC5
uA7808
TO220
IC6
uA7908
TO220
T1
BC546B
TO92
9332-377-801**
T102 BC546B
TO92
9332-377-801**
T202 BC546B
TO92
9332-377-801**
T302 BC546B
TO92
9332-377-801**
44
Philips Semiconductors
Video Amplifier Board
with TDA4885 and CR6927
Application Note
AN97039
APPENDIX 8: POWER DISSIPATION CR6927
In order to calculate the necessary heatsink size for the video module, the maximum power dissipation of the
video module has to be calculated. The power dissipation of an active load amplifier can be calculated by adding
static and dynamic power. Static power is dissipated in the emitter resistors, the bias resistors R1, R2 and R3
(see figure 5) and Rfb. The DC current IDC is specified in its data sheet to be 30mA (Vsup = 78 V) for one channel.
Equation 11 below calculates static power of one channel:
Dynamic power is mainly dissipated in the buffer transistors and depends on output voltage swing, load and
internal capacitance and switching frequency. Equation 12 defines dynamic power dissipation of one colour
channel.
Equ. 12
Where b is the blanking factor, during this part of a line time, there is no video signal. Power dissipating load
capacitance is defined in equation 4 of paragraph 4.1 and internal (of buffer transistors CR6927) capacitance is
2.4 pF, adding up to: 8.95pF + 2.4pF = 11.35 pF. Maximum voltage swing is 50 V, Cload,dissipating = 11.35 pF and
fswitch = 100 MHz. Equation 13 specifies the maximum dynamic power for one channel:
Equ. 13
Total maximum power dissipation is the sum of static and dynamic power dissipation, yielding:
3 * (2.3+3.3) = 16.8 W.
45
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