TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 30

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TEA2028 - TEA2029 APPLICATION NOTE
MAXIMUM CAPTURE TIME
The worst case capture time occurs when the first
sync pulse just precedes the sync window.
Let’s find the number of periods necessary for the
capture to occur, i.e. tn = 0.
- 50Hz : the number of periods is 6
- 60Hz : the number of periods is 3
Figure 59
V.6.3.3 - Frame blanking signal
This signal is necessay to blank the display during
each frame flyback. It is triggered at the beginning
of frame saw-tooth flyback. The duration of this
signal is 1.344ms (or 21 lines).
This ”frame blanking” signal is available through
Pin 4 (TEA2028 only) which is an open-collector
Figure 60
30/46
Frame
Sawtooth
Sync
Pulses
n
First Frame
Second Frame
Frame Blanking
(Pin 4)
T
T
CAPTURE(MAX)
CAPTURE(MAX)
T
L
T
L
T
SYNC
T
W
0
T
SYNC
, T
= 120ms
= 50ms
* 24 lines for TEA2029C
t
T
L
1
L
23ms , T
t
2
Window
Wide
W
(capture)
7.3ms
t
N
= 0
t
W
(21 lines)*
1.344ms
output.
It is also present within the normalized super sand-
castle signal on Pin 11 (TEA2028 and TEA2029).
V.6.3.4 - Frame blanking safety (TEA2028 only,
for TEA2029 refer to section VII.5)
Its duty is to protect the phosphor coating of picture
tube in case of any problem with vertical deflection
function such as scanning failure.
A signal to monitor correct scanning is provided by
the frame yoke and applied to Pin 2.
In case of any failure, all frame blanking outputs are
disabled and go high thereby blanking the entire
screen.
During trace phase, the voltage across frame yoke
has a parabolical shape due to the coupling capaci-
tor in series with yoke. During frame flyback, the
current through frame yoke must be rapidly in-
verted. Conventionally, a two-fold higher supply
voltage is applied across the yoke. This will pro-
duce an overvoltage called ”flyback”.
The safety monitoring status is detected on the
falling-edge of flyback, i.e. at the beginning of
scanning. A differentiator network is used to trans-
mit only fast voltage variations.
The required pulse is then compared to 1.26Vlevel.
Frame blanking goes high in the absence of nega-
tive pulse (zero deflection current) or if the pulse
does not fall within the first 21 lines (exagerated
over-scanning).
L335
20 s
L22
12 s