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参数资料
| 型号： | TC820CKW |
| 元件分类： | ADC |
| 英文描述： | 1-CH DUAL-SLOPE ADC, PQFP44 |
| 封装： | PLASTIC, FP-44 |
| 文件页数： | 6/24页 |
| 文件大小： | 185K |
| 代理商： | TC820CKW |
14
3-3/4 A/D Converter with Frequency
Counter and Logic Probe
TC820
TC820-10 10/17/96
2001 Microchip Technology Inc.
DS21476A
Table 1. TC820 Control Input Truth Table
Logic Input
FREQ/
RANGE/
TC820
VOLTS
FREQ
LOGIC
Function
X
1
Logic Probe
0
A/D Converter,
VFULL SCALE = 2
VREF
0
1
0
A/D Converter,
VFULL SCALE = 20
VREF
1
Frequency
0
Frequency Counter
Counter Input
NOTES: 1. Logic "0" = DGND
2. Logic "1" = VDD
Figure 9. Common-Mode Voltage Reduces Available
Integrator Swing (VCOM
VIN)
+
–
+
–
RI
CI
VI
VIN
INTEGRATOR
INPUT
BUFFER
+
–
TI= Integration Time =
CI= Integration Capacitor
RI= Integration Resistor
4000
f
VCM
OSC
Where:
VI =
[
VCM
VIN
–
TI
RI CI
FREQ/VOLTS
This input determines whether the TC820 is in the
analog-to-digital conversion mode or in the frequency
counter mode. When FREQ/VOLTS is connected to VDD,
the TC820 will measure frequency at the RANGE/FREQ
input. When unconnected, or connected to DGND, the
TC820 will operate as an analog-to-digital converter. This
input has an internal 5
A pulldown to DGND.
LOGIC
The LOGIC input is used to activate the logic probe
function. When connected to VDD, the TC820 will enter the
logic probe mode. The LCD will show "OL" and all decimal
points will be off. The decimal point inputs directly control
"high" and "low" display annunciators. When LOGIC is
unconnected, or connected to DGND, the TC820 will per-
form analog-to-digital or frequency measurements as se-
lected by the FREQ/VOLTS input. The LOGIC input has an
internal 5
A pulldown to DGND.
system where input signals are not referenced (float)
with respect to the TC820 power source. The analog
common potential of VDD – 3.3V gives a 7V end-of-battery-
life voltage. The analog common potential has a voltage
coefficient of 0.001%/%.
With a sufficiently high total supply voltage (VDD – VSS
> 7V), analog common is a very stable potential with
excellent temperature stability (typically 35ppm/
°C). This
potential can be used to generate the TC820 reference
voltage. An external voltage reference will be unnecessary
in most cases, because of the 35ppm/
°C temperature
coefficient. See the applications section for details.
Function Control Input Pin
Functional Description
The TC820 operating modes are selected with the
function control inputs. The control input truth table is
shown in Table I. The high logic threshold is
≥ VDD - 1.5V
and the low logic level is
≤ DGND +1.5V.
RANGE/FREQ
The function of this dual-purpose pin is determined by
the FREQ/VOLTS input. When FREQ/VOLTS is connected
to VDD, RANGE/FREQ is the input for the frequency counter
function. Pulses at this input are counted with a time base
equal to fOSC/40,000. Since this input has CMOS input
levels (VDD - 1.5V and DGND +1.5V), an external buffer is
recommended.
When the TC820 analog-to-digital converter function is
selected, connecting RANGE/FREQ to VDD will divide the
integration time by 10. Therefore, the RANGE/FREQ input
can be used to perform a 10:1 range change without
changing external components.
DP0/LO, DP1/HI
The function of these dual-purpose pins is determined
by the LOGIC input. When the TC820 is in the analog-to-
digital converter mode, these inputs control the LCD deci-
mal points. The decimal point truth table is shown in Table II.
These inputs have internal 5
A pull-downs to DGND when
the voltage/frequency measurement mode is active.
Table 2. TC820 Decimal Point Truth Table
Decimal Point Inputs
DP1
DP0
LCD
0
3999
0
1
399.9
1
0
39.99
1
3.999
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