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參數(shù)資料
| 型號(hào)： | ZN447E |
| 英文描述： | Converter IC |
| 中文描述： | 轉(zhuǎn)換器IC |
| 文件頁數(shù)： | 9/18頁 |
| 文件大小： | 289K |
| 代理商： | ZN447E |
ZN448/9
9
REFERENCE
(a) Internal reference
The internal reference is an active bandgap circuit which is
equivalent to a 2.5V Zener diode with a very low slope
impedance (Fig.11). A Resistor (R
REF
) should be connected
between pins 8 and 10.
The recommended value of 390
will supply a nominal
reference current of (5 - 2.5)/0.39=6.4mA. A stabilising/
decoupling capacitor, C
(4
μ
7), is required between pins 8
and 9. For internal reference operation V
REF OUT
(pin 8) is
connected to V
REF IN
(pin 7).
UP to five ZN448/9's may be driven from one internal
reference, there being no need to reduce R
REF
. This useful
feature saves power and gives excellent gain tracking
between the converters.
Alternatively the internal reference can be used as the
reference voltage for other external circuits and can source or
sink up to 3mA.
(b) External reference
If required an external reference in the range +1.5 to +3.0V
may be connected to V
. The slope resistance of such a
reference source should be less than 2.5
, where n is the
n
number of converters supplied.
GROUND
(PIN 9)
CREF
(0.47μ)
RREF
(390)
VREFOUT
(PIN 8)
VCC +5V
(PIN 10)
Fig.11 Internal voltage reference
RATIOMETRIC OPERATION
If the output from a transducer varies with its supply then an
external reference for the ZN4448/9 should be derived from
the same supply. The external reference can vary from +1.5
to +3.0V. The ZN448/9 will operate if V
is less than +1.5V
but reduced overdrive to the comparator will increase its delay
and so the conversion time will need to be increased.
COMPARATOR
The ZN448/9 contains a fast comparator, the equivalent input
circuit of which is shown in Fig.12. A negative supply voltage
is required to supply the tail current of the comparator.
However as this is only 25 to 150
μ
A and need not be well
stabilised it can be supplied by a simple diode pump circuit
driven from the
BUSY
output.
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