TC826CBU データシートの表示（PDF） - TelCom Semiconductor Inc => Microchip
部品番号
コンポーネント説明
メーカー
TC826CBU Datasheet PDF : 12 Pages
| |||
A/D CONVERTER WITH
BAR GRAPH DISPLAY OUTPUT
1
TC826
The internal voltage reference potential availabe at
analog-common will normally be used to supply the convert-
ers reference. This potential is stable whenever the supply
potential is greater than approximately 7V. In applications
where an externally generated reference voltage is desired
refer to Figure 6.
The reference voltage is adjusted with a near full-scale
input signal. Adjust for proper LCD display readout.
V+
8
V+
TC826
5
REF IN
ANALOG 2
COMMON
(b)
TC9491CZM
1.2V
REFERENCE
Figure 6. External Reference
Components Value Selection
Integrating Resistor (RINT)
The desired full-scale input voltage and output current
capability of the input buffer and integrator amplifier set the
integration resistor value. The internal class A output stage
amplifiers will supply a 1µA drive durrent with minimal
linearity error. RINT is easily calculated for a 1µA full-scale
current:
RINT = Full-Scale Input Voltage (V) = VFS
1 x 10 –6
1 x10–6
Where VFS = Full-Scale Analog Input
Integrating Capacitor (CINT)
The integrating capacitor should be slected to maximize
intgrator output swing. The integrator output will swing to
within 0.4V of VS+ or VS– without saturating.
The integrating capacitor is easily calculated:
( ) CINT = VFS
RINT
640
FOSC x VINT
Where :
VINT = Integrator Swing
FOSC = Oscillator Frequency
The integrating capacitor should be selected for low
dielectric absorption to prevent roll-over errors. Polypro-
pylene capacitors are suggested.
TELCOM SEMICONDUCTOR, INC.
Auto-Zero Capacitor (CAZ)
2 CAZ should be 2–3 times larger than the integration
capacitor. A polypropylene capacitor is suggested. Typical
values from 0.14µF to 0.068 µF are satisfactory.
Reference Capacitor (CREF)
A 1 µF capacitor is suggested. Low leakage capacitors
such as polypropylene are recommended.
Several capacitor/resistor combinations for common
full-scale input conditions are given in Table 1.
3
Table 1 Suggested Component Values
2V
200 mV
20 mV
Full-Scale Full-Scale Full-Scale
Component VREF ≈ 1V VREF ≈ 100 mV VREF ≈ 10 mV
RINT
CINT
CREF
CAZ
ROSC
2 MΩ
0.033µF
1µF
0.068µF
430kΩ
200kΩ
0.033µF
1µF
0.068µF
430kΩ
20kΩ
0.033µF
1F
4
0.14µF
430kΩ
NOTES: Approximately 5 conversions/second.
Differential Signal Inputs
5 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 system) and –IN is con-
nected to analog–common (VCOM).
In systems where common–mode rejection ratio mini-
mizes error. Common–mode voltages do, however, affect
6 the integrator output level. Integrator output saturation 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 recom-
mended 2V full–scale swing. The integrator output will swing
within 0.3V of VDD or VSS without increased linearity error.
Digital Section
7
The TC826 contains all the segment drivers necessary
to drive a liquid crystal display (LCD). An LCD backplane
driver is included. The backplane frequency is the external
clock frequency divided by 256. A 430kΩ OSC gets the
backplane frequency to approximately 55Hz with a 5V
nominal amplitude. When a segment driver is in phase with
8 the backplane signal the segment 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
3-179
Share Link: 