Datasheet

256 (DAC ladder resistance)
DAC digital code
  
  
 
SLAS062E − JANUARY 1987 − REVISED NOVEMBER 2008
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
Bandpass Out
High Pass
Out
30 k
Ω
47 pF
C3
R5
R4
R3
Low Pass Out
1000 pF
C2
C1
1000 pF
+
DACA
(R
1
)
(R
2
)
DACB
TLC7528
+
OUTA
RFBA
AGND
OUTB
REFB
RFBB
2
3
1
20
19
18
REFA
V
DD
CS
WR
DGND
DACA/DACB
DACA2 and DACB2
A3
+
A2
A1
DACA1 AND DACB1
Data In
V
I
DACA
/DACB
6
DGND
5
WR
16
CS
15
17
V
DD
REFA
4
18
19
20
1
3
2
RFBB
REFB
OUTB
AGND
RFBA
OUTA
+
TLC7528
DACB
(R
F
)
(R
S
)
DACA
Q=
R
3
R
4
R
F
R
S
R
F
R
fb(DACB1)
C
1
=C
2
,R
1
=R
2
,R
4
=R
5
G
−
30 k
Ω
10 k
Ω
A4
8
8
Data In
6
5
16
15
17
4
R
fb
is the internal resistor connected between OUTB and RFBB
Where:
Circuit Equations:
NOTES: A. Op-amps A1, A2, A3, and A4 are TL287.
B. CS
compensates for the op-amp gain-bandwidth limitations.
C. DAC equivalent resistance equals
Figure 10. Digitally-Controlled State-Variable Filter