11

Maxim 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 fC data strapped on D0–D6. This mode dis-

ables CS and WR controls, and filters A and B are pro-

grammed to the same fC.

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 fC of filters A and 8 directly (filters A and 8

are programmed to the same fC). 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

tWS

tWH

tWR

tAS

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

tAH

tDS

tDH

A0

SELECTS

Logic Low

Filter B

Logic High

Filter A

A1

A0

06

05

04

03

02

01

D0

FUNCTION

0

0

7-bit fC data

Selects filter A

0

1

7-bit fC data

Selects filter 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 enabled

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