Operating Temperature Range *

C to +70

18-Pin

Plastic Pin

Small Outline

Package

Package (SOIC)

ALD521DPD

ALD521DSD

Contact factory for industrial temperature range

FEATURES AND BENEFITS

· Low cost, simple functionality
· PC parallel printer port interface standard
· Support resolution up to 23 binary bits + sign

polarity bit

· Easy to use to acquire up to 23 bit linearity

and noise performance

· Integration time can be set by the user
· Easy user evaluation and setting of

conversion parameters

· Low power dissipation - 4 mA typical

including crystal oscillator

· On-chip Crystal Oscillator Circuit
· Two way asynchronous handshake data

transfer

· Conversion speed versus resolution trade-off
· Power down (sleep mode) control input to

power down to 2

· Chip Select control input
· High impedance DV, D

OUT

and S

CLK

when chip not selected

· Single 3 V to 5 V power supply

ALD521D

DVANCED

INEAR

EVICES,

NC.

ORDERING INFORMATION

24 BIT SERIAL INTERFACE DIGITAL CONTROLLER

APPLICATIONS

· Operate in conjunction with ALD500/ALD500R

Precision analog signal processors

· High accuracy DC voltage measurement functions
· Portable battery operated instruments
· PC-based software control or stand-alone operation (without

other processors or PC)

· Serial digital output interface to other microprocessors or

microcontrollers

GENERAL DESCRIPTION

The ALD521D is a digital controller designed to interface to the ALD500
or ALD500R integrating dual slope analog processors as a chip set for
building a precision analog-to-digital converter. With the ALD521D and
ALD500R, together with a few external capacitors and resistors, a
precision Analog to Digital converter with auto zero and auto-polarity
can be implemented.

The ALD521D can operate in either a stand-alone mode or in an
external microprocessor control mode. In the stand-alone mode, the
ALD521D can either making continuous measurements or a single
measurement. Under external microprocessor control, the ALD521D
can directly interact with a PC under PC software control via a standard
parallel printer port with no other components, or it can also communicate
with other microcontrollers serially.

The ALD500/ALD500R analog processors consist of on-chip digital
control circuitry to accept control inputs, integrating buffer amplifiers,
analog switches, and voltage comparators. It functions in four operating
modes, or phases, namely auto zero, integrate, deintegrate, and
integrator zero phases. At the end of a conversion, the comparator
output goes from high to low when the integrator crosses zero during
deintegration. ALD500 analog processors also provide direct logic
interface to CMOS logic families.

http://www.aldinc.com

PIN CONFIGURATION

Note: N/C - No Conncection

DGND

PWRUP

XTAL

OUT

PD, SD PACKAGE

OUT

V+

XTAL

OUT

N/C

ALD521D

CLK

ALD512D

Advanced Linear Devices

GENERAL DESCRIPTION (cont'd)

The ALD521D implements all the four phases of the ALD500
or ALD500R, namely auto zero, integrate, deintegrate, and
integrator zero phases. It also provides direct logic interface
to CMOS logic families. The ALD521D operates from an
external clock or its internal oscillator circuit along with an
external crystal. The internal system clock of the ALD521D
runs at a divide by 4 rate of the crystal or external clock

frequency.

A Data Valid (DV) low output during the auto zero phase
indicates when a 24 bit data word is available for output while
during the other phases DV remains in logical 1 state.

The ALD521D has control input pins for power down
(PWRUP), Chip Select (CS) and Integration time selection
(S1, S2 and S3). These pins can all be interfaced directly to
any 5V CMOS logic or microcontroller. They can also be
connected to a PC parallel printer port directly. When not
used, or if no programming control is desired, these pins can
be wired directly to their respective desired logic state, either
V+ or DGND (Ground).

Upon power on, the ALD521D initiates a power-on initializa-
tion cycle and resets all internal counters and registers. Then
it check the status of the PWRUPpin. A logical 0 on PWRUP
power up the ALD521D and a logical 1 on PWRUP power
down the ALD521D. If the ALD521D detects a logical 1 state
on the PWRUP pin, it in turn powers down the ALD500R to
save power during non-active period. At the same time, the
crystal oscillator circuit of the ALD521D is also stopped to
conserve power consumption. In power down mode the
current consumption of the ALD521D and the ALD500R is
less than 28

A. To start and power up the ALD521D again,

simply put a logical 0 on PWRUP. An external microcontroller
can therefore use this pin to control the ALD521D power-on

SELECTING INTEGRATION TIME

For maximum 50/60 cycle line power noise rejection, Inte-
gration time t

INT

must be picked as a multiple of the period of

line power frequency. For example, t

INT

times of 16.667

msec, 33.333 msec, 66.667 msec, 100 msec, 200 msec and
300 msec maximize 60 Hz line power noise rejection; and 20
msec, 50 msec, 100 msec, 200 msec and 300 msec
maximize 50 Hz line power noise rejection. In general, the
longer the integration time , the better the noise rejection of
the line power noise, but it also takes longer to complete a
conversion cycle. A default recommended integration time of
100 msec offer the best tradeoff between noise perfor-
mance, conversion time and 50/60 cycle line power noise
rejection. The 100 msec integration time also offers the
benefit of being universally optimal for both 50 cycle line
power noise rejection and 60 cycle line power noise
rejection.

SELECTIONS S1

INTEGRATION TIME

APPROXIMATE

NUMBER OF

PINS

[18]

[1]

[2]

CONVERSION/SECOND

AC CYCLES

16.667ms

33.333ms

50.000ms

66.667ms

100.000 ms

166.667 ms

200.000 ms

300.000 ms

ALD521D PIN CONFIGURATION FOR DIFFERENT INTEGRATION TIMES

Note:"0" = GND; "1" = V+

status. If power down feature is not used, then the PWRUP
pin must be grounded to leave the ALD521D in continuously
power-on mode.

Chip Select (CS) enable selection of the ALD521D controller
when this pin is at logical 0 (CS Input = GND). When not
selected, when the CS pin is at logical 1, the ALD521D places
the DV, D

OUT

and S

CLK

pins in high impedance mode.

Multiple ALD521D devices can have these three pins wired
in parallel to a same external controller. When data is
required from a specific ALD521D, it is selected by having
its CS pin set at logical 0 state. The external controller can
send CS to only one ALD521D during each conversion cycle.
The CS must be valid for the duration of at least one complete
conversion cycle in order for the measurement data to be
valid. From an external controller, CS can be generated by
a latched output pin.

ALD512D

Advanced Linear Devices

ABSOLUTE MAXIMUM RATINGS

Supply voltage, V

+7.0V

Differential input voltage range

-0.3V to V

+0.3V

Power dissipation

600 mW

Operating temperature range

PD, SD package

C to +70

Storage temperature range

-65

C to +150

Lead temperature, 10 seconds

+260

OPERATING ELECTRICAL CHARACTERISTICS
T

= 25

V+

= +5V unless otherwise specified

Parameter

Symbol

Min

Typ

Max

Unit

Test Conditions

Supply
Operating Voltage Range

V+

5.5

Supply Current

4.0

6.8

Input Characteristics
Low Input Voltage

-0.3

1.0

High Input Voltage

3.5

5.3

Input Leakage Current

-10

Output Characteristics
Low Output Voltage

0.2

0.8

High Output Voltage

3.6

4.8

= 10pF. Rise/Fall Times

R ,

125

nsec

Oscillator (OSC

IN,

OSC

OUT)

Crystal Frequency

XTL

3.6864

4.0

MHz

External Frequency (OSC

IN)

OSC

4.0

MHz

Timing Characteristics
Power Up Delay Time

msec

Chip Select Setup Time

1.1

sec

Chip Select Delay Time

Conv. Cycle

Data Valid Setup Time

sec

Data Valid Time Out Time

5.5

msec

Data Out Time

DOUT

500

nsec

Serial Clock Low Time

sec

Data Not Valid Time

DNV

sec

Integration Time

INT

16.666

300

msec

Integrator ZERO Time

INTZ

msec

Autozero Time

INT

msec

Chip Select Delay time (t

) may be as short as 7

sec, if start of auto zero phase cycle time could be

determined. For asynchoronous operation, t

must be for a minimum of one complete conversion cycle to

assure synchronization to start of auto zero phase cycle time.

These are typical practical limits for Integration time. Lower Integration time than the minimum allows more
conversion cycles per second at reduced count resolution. Higher Integration time increases count
resolution, but requires increased capacitor value and lowered number of conversion cycles per second.
Deintegration time depends on selection of full scale input range, integration capacitor value and voltage
reference.

ESD Sensitive Device. Stresses above those listed under Absolute Maximum Ratings may cause permanent
damage to device and may affect device reliability.

ALD512D

Advanced Linear Devices

SERIAL DATA TRANSFER

The ALD521D has an internal 23 bit binary counter that can
be clocked out serially at the end of an analog conversion
cycle, or conversion, in an asynchronous handshake mode
with an external processor. The ALD521D also determines
the sign bit for the ALD500R where a logic 1 is a positive sign
and a logic 0 is a negative sign. This sign bit is the 24th bit
being sent out by the ALD521D.

At the end ofeach conversion, the ALD521D transmits a 24
bit serial word which requires an external processor to send
in 24 serial clock pulses. This 24 bit serial word consists of
content from the 23 bit binary counter with MSB as the first bit,
LSB the 23rd bit, followed by a sign bit as the last bit. A
transition of DV from a high to low state signals a completed
conversion and readiness for the start of the serial data
transfer.

During a conversion, the ALD521D maintains DV in a high or
logic 1 state. When it completes a conversion, the ALD521D
sets the DV to low. Simultaneously, the ALD521D puts the first
bit of the 24 bit binary word (MSB bit) on Dout. For this first
serial bit out, an external processor has a maximum of 5.5
msec to read the data on Dout and send a serial clock pulse
back to the ALD521D. This serial clock consists of a high to
low transition followed by a low to high transistion on S

CLK

When the ALD521D receives an external serial clock on S

CLK

it resets the DV to a high logic 1 state. In addition, it internally
clocks the next serial bit onto Dout and sets the DV to a low
state again.

Similarly, the ALD521D asynchronously transfers the
remainder of the 24 bit serial word to the external processor.
When all 24 serial bits have been clocked out, the ALD521D
resets the DV to a high state, and starts the integration phase
of the conversion. It keeps DV high for the remainder four
phases of the conversion cycle.

For an external processor to interface to the ALD521D, it
needs a minimum of 2 input pins and one output pin dedicated
for the task. The ALD521D has DV (data valid), and Dout (data
out) as outputs and S

CLK

(serial input clock) as input. The

external processor can use either an interrupt or data input for
the interface to DV. After the ALD521D sends the first DV high
to low transition, it waits for a maximum of 5.5 milliseconds for
an external serial clock at the S

CLK

input. If an external serial

clock is not received during that time, the ALD521D times out
internally, sets the DV to a high state, and starts a new
conversion. For example, if a conversion cycle is equal to 200
msec., DV will not be valid until 200 msec. later. The external
processor can read DV as an interrupt to begin clocking the 24
bit data. The external processor can also sample DV as a data
input or it can synchronize to the A and B outputs of the
ALD521D to determine when the next serial word becomes
available.

INTERFACE TO ALD500R

The ALD521D has A and B outputs that control the four
conversion phases of the ALD500/ALD500R and has Cout as
an input from the ALD500/ALD500R. Note that Cout of the
ALD500/ALD500R must be connected to pin 3 and pin 8 of the
ALD521D.

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