TC826CBU データシートの表示（PDF） - TelCom Semiconductor Inc => Microchip
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TC826CBU Datasheet PDF : 12 Pages
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A/D CONVERTER WITH
BAR GRAPH DISPLAY OUTPUT
TC826
voltage across each LCD segment. This insures long LCD
display life. The polarity segment drive, –POL, is ‘ON’ for
negative analog inputs. If +IN and –IN are reversed this
indicator would reverse. The TC826 transfer function is
shown in Figure 7.
In the BAR display format the 41 bar segments and the
overrange annunciator, OR, will flash ON and OFF. The
flash rate is on fourth the conversion rate (FOSC/2560).
In the DOT display mode, OR flashes and all other data
segment drivers are off.
OVERRANGE
40
INDICATION
39
Polarity Indication (POL– Pin 60)
The TC826 converts and displays data for positive and
negative input signals. The POL– LCD segment driver (Pin
60) is active for negative signals.
2
1
–0.5 0
–2 –1
0.5 1
2
3 39 39.5 40 40.5
ANALOG INPUT
VFS
(X 40 )
Figure 7. TC826 Transfer Function
BAR/DOT Input (Pin 61)
The BAR/DOT input allows the user to select the display
format. The TC826 powers up in the BAR mode. Select the
DOT display format by connecting BAR/DOT to the negative
supply (Pin 12) through a 1MΩ resistor.
HOLD Input (Pin 62)
The TC826 data ouput latches are not updated at the
end of each conversion if HOLD is tied to the negative supply
(Pin 12) through a 1 MΩ resistor. The LCD display continously
displays the previous conversion results.
The HOLD pin is normally pulled high by an internal pull-
up.
TEST Input (Pin 63)
The TC826 enters a test mode with the TEST input
connected to the negative supply (Pin 12). The connection
must be made through a 1MΩ resistor. The TEST input is
normally internally pulled high. A low input sets the output
data latch to all ones. The BAR display mode is set. The 41
LCD output segments (zero plus 40 data segments) and
overrange annuniciator flash on and off at 1/4 the conversion
rate. The polarity annunciator (POL–) segment will be on but
not flashing
Oscillator Operation
The TC826 external oscillator frequency, FOSC, is set
by resistor ROSC connected between pins 13 and 14. The
oscillator frequency versus resistance curve is shown in
Figure 8.
50 20
18
40 16
14
TA = 25°C
VDDTO VSS= 9V
30 12
10
20 8
6
10 4
2
00
0 2 4 6 8 10 12 14 16 18 20
ROSC (X 100kΩ)
Figure 8. Oscillator Frequency vs. ROSC
FOSC is divided by 32 to provide an internal system
clock, FYSY. Each conversion requires 80 internal clock
cycles. The internal system clock is divided by 8 to provide
the LCD backplane drive frequency. The display flash rate
during an input out-of-range signal is set by dividing FSYS
by 320.
The internal oscillator may be bypassed by driving OSCI
(Pin 13) with an external signal generator. OSC2 (Pin 14)
should be left unconnected.
The oscillator should swing from VDD to VSS in single
supply operation (Figure 9). In dual supply operation the
signal should swing from power supply ground to VDD.
Overrange Display Operation (OR, Pin 59)
An out–of–range input signal will be indicated on the
LCD display by the OR annunciator driver (Pin 59) becoming
active.
3-180
TELCOM SEMICONDUCTOR, INC.
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