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TC7129 参数 Datasheet PDF下载

TC7129图片预览
型号: TC7129
PDF下载: 下载PDF文件 查看货源
内容描述: 4-1 / 2位ANALOG -TO -DIGITAL具有片上LCD驱动器转换器 [4-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTER WITH ON-CHIP LCD DRIVERS]
分类和应用: 驱动器转换器
文件页数/大小: 15 页 / 213 K
品牌: TELCOM [ TELCOM SEMICONDUCTOR, INC ]
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4-1/2 DIGIT ANALOG-TO-DIGITAL  
CONVERTER WITH ON-CHIP LCD DRIVERS  
3
TC7129  
Integrating Capacitor (CINT  
)
Voltage Reference (DREF, RREF, RBIAS, CRF)  
The charge stored in the integrating capacitor during  
the integrate phase is directly proportional to the input  
voltage. The primary selection criterion for CINT is to choose  
a value that gives the highest voltage swing while remain-  
ing within the high-linearity portion of the integrator output  
range. An integrator swing of 2V is the recommended  
value. The capacitor value can be calculated from the  
equation:  
A TC04 band-gap reference provides a high-stability  
voltage reference of 1.25V. The reference potentiometer  
(RREF) provides an adjustment for adjusting the reference  
voltage; any value above 20 kis adequate. The bias  
resistor (RBIAS) limits the current through DREF to less than  
150 µA. The reference filter capacitor (CRF) forms an RC  
filter with RBIAS to help eliminate noise.  
Input filter (RIF, CIF)  
tINT x IINT  
CINT  
=
,
For added stability, an RC input noise filter is usually  
included in the circuit. The input filter resistor value should  
not exceed 100 k. A typical RC time constant value is  
16.7msec to help reject line-frequency noise. The input filter  
capacitor should have low leakage for a high-impedance  
input.  
VSWING  
where tINT is the integration time.  
Using the values derived above (assuming 60 Hz  
operation), the equation becomes:  
Battery  
16.7msec x 13.3 µA  
CINT  
=
= 0.1 µF.  
2V  
The typical circuit uses a 9V battery as a power source.  
Any value between 6V and 12V can be used. For operation  
from batteries with voltages lower than 6V and for operation  
from power supplies, see "Powering the TC7129."  
The capacitor should have low dielectric absorption to  
ensure good integration linearity. Polypropylene and Teflon  
capacitors are usually suitable. A good measurement of the  
dielectric absorption is to connect the reference capacitor  
across the inputs by connecting:  
SPECIAL APPLICATIONS  
The TC7129 as a Replacement Part  
Pin to Pin  
20 33 (CREF+ to IN HI)  
30 32 (CREFto IN LO)  
The TC7129 is a direct pin-for-pin replacement part for  
the ICL7129. Note, however, that part requires a capacitor  
and resistor between pins 26 and 28 for phase compensa-  
tion. Since the TC7129 uses internal phase compensation,  
these parts are not required and, in fact, must be removed  
from the circuit for stable operation.  
A reading between 10,000 and 9998 is acceptable;  
anything lower indicates unacceptably high dielectric ab-  
sorption.  
Reference Capacitor (CREF  
)
Powering the TC7129  
The reference capacitor stores the reference voltage  
during several phases of the measurement cycle. Low  
leakageistheprimaryselectioncriterionforthiscomponent.  
The value must be high enough to offset the effect of stray  
capacitance at the capacitor terminals. A value of at least  
1 µF is recommended.  
While the most common power source for the TC7129  
is a 9V battery, there are other possibilities. Some of the  
more common ones are explained below.  
TELCOM SEMICONDUCTOR, INC.  
3-237