Datasheet

11Maxim Integrated
Digitally-Programmed, Dual
2nd-Order Continuous Lowpass Filter
MAX270/MAX271
Table 2. MAX271 µP-Mode Interface
MAX270 Control Interlace
The A0 pin is a three-level input that selects the memory
addresses for updating cutoff frequency data in FP mode:
Figure 2 shows µP-mode interface timing.
Connecting A0 to the negative supply selects pin-strap
mode. Pin-strap mode allows filter programming with
no timing requirements. Internal memory latches are
disabled, permitting filters A and B to be programmed
directly to f
C
data strapped on D0–D6. This mode dis-
ables CS and WR controls, and filters A and B are pro-
grammed to the same f
C
.
A low level on the SHDN pin shuts down all amplifiers
and disconnects OUTA, OUTB, and OP OUT. Current
consumption drops to less than 15µA in this mode.
MAX271 Control Interlace
Connecting the MODE pin to GND or V- selects the
µP mode. In this mode, addressable program memory
controls filter cutoff frequency programming and all T/H
functions, except T/H. See the Figure 2 for timing charac-
teristics. Table 2 describes available functions:
In FP mode, SHDN, T/H A/B, and T/H EN pins are dis-
abled. T/H remains enabled and performs the T/H track-
ing/holding function.
Tying MODE to V+ selects pin-strap mode. In this mode,
both memory latches are transparent, and data on D0–D6
controls the f
C
of filters A and 8 directly (filters A and 8
are programmed to the same f
C
). Pin strap D0–D6 for
operation without FP. A0, A1, CS, and WR are disabled.
X = Don't care
Figure 2. MAX270/MAX271 Digital Timing Diagram
CS
t
WS
t
WH
t
WR
t
AS
WR
ADDRESS
(A0, A1)
DATA
(D0-D6)
NOTE : ALL DIGITAL INPUTS ARE LEVEL-SENSITIVE. WHEN WR AND CS ARE BOTH LOW,
THE DATA INPUT LATCHES ARE TRANSPARENT. AND THE FILTERS ARE
PROGRAMMED TO THE DATA ON D0–D6
t
AH
t
DS
t
DH
A0 SELECTS
Logic Low Filter B
Logic High Filter A
A1 A0 06 05 04 03 02 01 D0 FUNCTION
0 0 7-bit f
C
data Selects
f ilte r A
0 1 7-bit f
C
data Selects f il t e r B
1 0 X X X X X X 0 T/H OUT disabled
1 0 X X X X X X 1 T/H OUT e n ab le d
1 0 X X X X X 0 X Selects OUTB as input to T /H
1 0 X X X X X 1 X Selects OUTA as input to T /H
1 1 X X X X X X 0
Filter shutdown mode. All outputs floated, 15µA
max supply current
1 1 X X X X X X 1 Removes filter from shutdown mode