LTC1564C View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1564C' PDF : 12 Pages View PDF
LTC1564
PI FU CTIO S
IN (Pin 16): Analog Input. The filter in the LTC1564 senses
the voltage difference between the IN and AGND pins. In
normal filtering (EN = 0, RST = 1, F code other than 0000),
the IN pin connects within the LTC1564 to a digitally
controlled resistance whose other end is a current-sum-
ming point at the AGND potential. At unity gain (G code
0000), the value of this input resistance is nominally 10k
and the IN voltage range is rail-to-rail (V+ to V–). When
filtering at gain settings above unity (G code ≠ 0000), the
input resistance falls as (1/gain) to nominally 625Ω at a
gain of 16 (G code 1111) and the linear input range also
falls in inverse proportion to gain. (The variable gain
capability is designed to boost lower level input signals
with good noise performance.) Input resistance does not
vary significantly with the frequency-setting F code ex-
cept in the mute state (F code 0000). In either the mute
state (F code 0000 or RST = 0) or the shutdown state (EN
= 1 or EN open circuited), analog switches disconnect the
IN pin internally and this pin presents a very high input
resistance. Circuitry driving the IN pin must be compat-
ible with the LT1564’s input resistance and with the
variation of this resistance in the event that the LTC1564
is used in multiple modes. Signal sources with significant
output resistance may introduce a gain error as the
source’s output resistance and the LTC1564’s input resis-
tance form a voltage divider. This is especially true at the
higher gain or G code settings where the LTC1564’s input
resistance is lowest.
In single supply voltage applications with elevated gain
settings (G code ≠ 0000) it is important to keep in mind
that the LTC1564’s ground reference point is AGND, not
V–. With increasing gains, the LTC1564’s linear input
voltage range is no longer rail-to-rail but converges
toward AGND. Similarly the OUT pin swings positive or
negative with respect to AGND. At unity gain (G code
0000), both IN and OUT voltages can swing from rail-to-
rail.
BLOCK DIAGRA
IN
V+
VARIABLE
GAIN
OUT
AMPLIFIER
PROGRAMMABLE FILTER
V+
SHUTDOWN
SWITCH
R
V–
R
CMOS LATCH
CS/HOLD
RST
SHUTDOWN
EN
SWITCH
1564 F03
AGND
G3 G2 G1 G0
F3 F2 F1 F0
V–
Figure 3. Block Diagram
8
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