参数资料
型号: TC826CBUTR
元件分类: ADC
英文描述: 1-CH DUAL-SLOPE ADC, PQFP64
封装: PLASTIC, QFP-64
文件页数: 3/18页
文件大小: 348K
代理商: TC826CBUTR
2005 Microchip Technology Inc.
DS21477C-page 11
TC826
TABLE 4-2:
SUGGESTED COMPONENT
VALUES
4.5
Differential Signal Inputs
The TC826 is designed with true differential inputs and
accepts input signals within the input stage Common
mode voltage range (VCM). The typical range is V+ -1
to V- +1V. Common mode voltages are removed from
the system when the TC826 operates from a battery or
floating power source (isolated from measured sys-
tem) and -IN is connected to analog common (VCOM).
In systems where Common mode rejection ratio mini-
mizes error. Common mode voltages do, however,
affect the integrator output level. Integrator output sat-
uration must be prevented. A worse case condition
exists if a large positive VCM exists in conjunction with
a full scale negative differential signal. The negative
signal drives the integrator output positive along with
VCM. For such applications, the integrator output swing
can be reduced below the recommended 2V full scale
swing. The integrator output will swing within 0.3V of
VDD or VSS without increased linearity error.
4.6
Digital Section
The TC826 contains all the segment drivers necessary
to drive a liquid crystal display (LCD). An LCD back-
plane driver is included. The backplane frequency is
the external clock frequency divided by 256. A 430k
Ω
OSC gets the backplane frequency to approximately
55Hz, with a 5V nominal amplitude. When a segment
driver is in phase with the backplane signal, the seg-
ment is ‘OFF’. An out-of-phase segment drive signal
causes the segment to be ‘ON’ or visible. This AC drive
configuration results in negligible DC 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 4-4:
TRANSFER FUNCTION
4.7
BAR/DOT Input (Pin 61)
The BAR/DOT input allows the user to select the dis-
play 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 1M
Ω resistor.
4.8
HOLD Input (Pin 62)
The TC826 data output latches are not updated at the
end of each conversion if HOLD is tied to the negative
supply (Pin 12) through a 1M
Ω resistor. The LCD dis-
play continuously displays the previous conversion
results.
The HOLD pin is normally pulled high by an internal
pull-up.
4.9
TEST Input (Pin 63)
The TC826 enters a Test mode with the TEST input
connected to the negative supply (Pin 12). The connec-
tion must be made through a 1M
Ω 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 over range annunciator flash on
and off at 1/4 the conversion rate. The polarity annun-
ciator (POL-) segment will be on, but not flashing.
4.10
Over Range 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.
In the BAR display format, the 41 bar segments and the
over range 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.
Comp.
2V
Full Scale
VREF ≈ 1V
2mV
Full Scale
VREF ≈ 100V
20mV
Full Scale
VREF ≈ 10V
RINT
2M
Ω
200k
Ω
20k
Ω
CINT
0.033
μF
0.033
μF
0.033
μF
CREF
1
μF
1
μF
1
μF
CAZ
0.068
μF
0.068
μF
1.14
μF
ROSC
430k
Ω
430k
Ω
430k
Ω
Note: Approximately 5 conversions/second.
40
39
2
1
0
-1
-2
1
2
3
39 39.5 40 40.5
-0.5
0.5
Digital
Display
Over Range
Indication
Analog Input
(X
VFS
40
)
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