MAX1253BEUE+ Datasheet MAX1253BEUE+, MAX1254BEUE+, MAX1253BEUE+T | P22-P24

MAX1253/MAX1254

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V

Monitor

22 ______________________________________________________________________________________

Upper Threshold Register

A conversion result greater than the value stored in the

upper threshold register results in a fault, increasing

the internal fault counter by one. When the fault count

exceeds the value stored in fault bits B7–B4 of the

channel configuration register, the channel’s alarm bits

in the alarm register are set, resulting in an interrupt on

INT.

The upper threshold register data format must be the

same as the input channel. When the input channel is

configured for single-ended or differential unipolar volt-

age measurements, data stored in the upper threshold

nels configured for temperature measurements or as

differential bipolar voltage inputs, the upper threshold

the register with FFF hex to disable upper threshold

faults in unipolar mode, and 7FF hex in temperature or

bipolar mode. The power-up/reset default is FFF hex.

See the Command Word section on how to read/write

to the upper threshold registers.

Lower Threshold Register

Conversion results lower than the value stored in the

lower threshold register increment the internal fault

counter. Considerations about channel configuration

mat are the same as for the upper threshold register.

Set the register to 000 hex to disable lower threshold

faults in unipolar mode, or to 800 hex in temperature or

bipolar mode. The power-up/reset default is 000 hex.

See the Command Word section on how to read/write

to the lower threshold registers.

Current Data Registers

The current data register holds the last conversion

result or the digitally averaged result, when enabled

(see the Averaging section). The current data registers

default to 800 hex at power-up/reset and can be read

from and written to through the serial interface. See the

Command Word section on how to read/write to the

current data registers.

INT Interrupt Output

INT provides an indication that an alarm has occurred

in the system. It can be programmed (see Table 9) to

operate as a push-pull digital output or as an open-

drain output (requiring either a pullup or a pulldown

resistor) for wired-OR interrupt lines. Bits B3 and B4 in

the setup register configure INT and determine its

response to an alarm event.

When an internal fault counter exceeds the threshold

stored in the fault bits (B7–B4) of the corresponding chan-

nel configuration register, the alarm bits for that particular

channel are updated to indicate an alarm. When any bit in

the alarm register is set, the INT output becomes active,

and stays active until all alarm bits are cleared. See the

Alarm Register section for more information.

Servicing Interrupts at INT

After detecting an interrupt on INT, the µC’s interrupt

routine should first read the alarm register to find the

source of the alarm and reset the alarm bits by using

any of the methods described in the Alarm Register

section. Then it can continue with any other action

required by the application to react to the alarm.

Note: Multiple alarm conditions can be present. The

INT remains active until all alarm conditions have been

cleared.

Performing Conversions

At power-up or after a RESET command, the

MAX1253/MAX1254 default to shutdown mode with all

channels enabled, set for single-ended voltage mea-

surements, and with the scan mode set to manual. Start

a conversion by issuing a manually triggered conver-

sion command with the address bits of the channel

selected (see the Manual Conversion section for more

details) or by setting automatic scan mode. To place

the MAX1253/MAX1254 in automatic scan mode, set

scan mode bit B2 in the setup register to logic 1.

In automatic scan mode, the MAX1253/MAX1254 con-

vert all enabled channels starting with the internal tem-

perature sensor, followed by the V

monitor, then by

AIN0 to AIN7. As the scan sequence progresses, the

analog inputs are converted and the resulting values

are stored for each channel into its current data regis-

ter. Once the scan cycle completes, the MAX1253/

MAX1254 wait a period determined by the sample wait

bits (B7, B6, B5) in the setup register and then repeat

the scan cycle.

After configuring the MAX1253/MAX1254 with automat-

ic scan mode enabled, the devices do not require any

intervention from the system µC until an alarm is trig-

gered. All conversion and monitoring functions can

continue running indefinitely.

Manual Conversion

In manual mode (scan mode bit in the setup register

set to zero, the default after power-up/reset), the

MAX1253/MAX1254 convert individual channels with

the Manually Triggered Conversion command.

Assuming that, either by power-up/RESET defaults or

by previous initialization, the channel to be addressed

is both enabled and configured for the type of signal to

be acquired (voltage/temperature, single ended/differ-

MAX1253/MAX1254

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V

Monitor

______________________________________________________________________________________ 23

ential, or unipolar/bipolar), carry out the following steps

to execute a manual conversion. See Figure 9 for man-

ual conversion timing:

1) Disable autoscan (set up register scan mode bit to

zero), if necessary.

2) Pull CS low.

3) Initiate a conversion by issuing a Manually Triggered

Conversion command (0000, followed by the

address bits of the channel to be converted).

4) Pull CS high to start the conversion.

5) Maintain a logic high on CS to allow for reference

power-up (if the reference mode requires it) and

conversion time.

6) Pull CS low.

7) Issue a Read Current Data Register for Selected-

Channel command (0010, followed by the same

address of the channel in the Manually Triggered

Conversion command).

Voltage Measurements

Every voltage measurement (internal V

or external

input channel) requires 10.6µs to complete. If the inter-

nal reference needs to power up (reference mode =

01), an additional 40µs is required every time the

MAX1253/MAX1254 come out of automatic shutdown

mode after a sample wait period greater than 80µs.

Monitoring V

This internal acquisition channel samples and converts

the supply voltage, V

value can be calculated from the digitized data

with the following equation:

The reference voltage must be larger than 1/2V

for

the operation to work properly. V

monitoring requires

10.6µs (typ) per measurement.

Temperature Measurement

The MAX1253/MAX1254 perform temperature measure-

ment by measuring the voltage across a diode-con-

nected transistor at two different current levels. The

following equation illustrates the algorithm used for

temperature calculations:

where:

HIGH

= sensor-diode voltage with high current flowing

HIGH

)

LOW

= sensor-diode voltage with low current flowing

LOW

)

q = charge of electron = 1.602 ✕ 10

-19

coulombs

k = Boltzman constant = 1.38 ✕ 10

-23

J/K

n = ideality factor (slightly greater than 1)

temperature V V x

HIGH LOW













()-

nxln

High

LOW

V x current data register content x

REF













4096

(__ _ )

C2 C1 C0 A2 A1 A0

SCLK

DIN

DOUT

C3 C2 C1 C0 A2 A1 A0A3A3

PU+CONV

Figure 9. Manual Conversion Timing Without Reading Data

MAX1253/MAX1254

Stand-Alone, 10-Channel, 12-Bit System Monitors

with Internal Temperature Sensor and V

Monitor

24 ______________________________________________________________________________________

The temperature measurement process is fully auto-

mated in the MAX1253/MAX1254. All steps are

sequenced and executed by the MAX1253/MAX1254

each time an input channel (or an input channel pair)

configured for temperature measurement is scanned.

The resulting 12-bit, two’s complement number repre-

sents the sensor temperature in degrees Celsius, with

1 LSB = +0.125°C.

The MAX1253/MAX1254 support both single-ended

and differential temperature measurements.

Applications Information

Setting Up the

MAX1253/MAX1254 Subsystem

The MAX1253/MAX1254 are autonomous subsystems,

requiring only initialization to scan, convert, and monitor

the voltage signals or the temperature sensors con-

nected to their input channels.

For simple applications, using any number of the input

channels and any combination of voltage/temperature

and unipolar/differential, with no interrupt generation

required, use the following intitialization procedure:

• Issue a Write Global Configuration Registers com-

mand. This is a single, 5-byte write operation that con-

figures the input channels, enables the channels to be

used, sets the sample wait time between scans, con-

figures the interrupt output INT, selects the reference

mode, and starts the automatic scan mode. See the

Write Global Configuration Registers Command sec-

tion, Table 2, and Tables 5–10.

Immediately after the global configuration register is

loaded, the MAX1253/MAX1254 begin to update the

current data registers. Acquire conversion data from

the MAX1253/MAX1254 by issuing a command to read

a specific channel with the Read Current Data Register

for Selected Channel command. Read all current data

registers at once with the Read Current Data Registers

for All Channels command.

For more complex applications, the monitoring and

interrupt generation features of the MAX1253/MAX1254

require a second step of initialization. Each enabled

channel to be monitored requires configuration using a

Write Configuration Register for Selected Channel com-

mand. Each command is a 5-byte write that sets the

upper and lower fault thresholds, the number of faults for

an alarm before an interrupt is generated, and an aver-

age algorithm parameter if the application requires input

signal filtering.

Applications can read the current data registers and

respond to interrupts signaled by the INT output (see

the Servicing Interrupts at INT section).

All the MAX1253/MAX1254 registers can be verified by

reading back written data, including the configuration

registers. This feature is useful for development and

testing (see Table 2).

Power-Up/Reset Defaults Summary

Setup Register Power-Up/Reset Defaults

At initial power-up or after a RESET command, the

setup register resets to 00 hex. Consequently, the

MAX1253/MAX1254 are configured as follows:

• Sample wait time is 0µs.

• INT output is open drain and outputs an active-low

signal to signify an alarm.

• Manual conversion mode.

• External reference for voltage measurements.

Table 15. Power-Up/Reset Defaults Summary

Setup B0 to B7 All 0s See Setup Register Power-Up/Reset Defaults

Channel enable B0 to B11 All 1s All channels (int/ext) enabled

Input configuration B0 to B11 All 0s All single-ended voltage inputs

Alarm register B0 to B23 All 0s No alarms set

Channel configuration B0 to B7 All 0s Faults = 0, no averaging

Upper threshold B0 to B9 All 1s All upper thresholds max range

Lower threshold B0 to B9 All 0s All lower thresholds min range

Current data registers B0 to B9 200hex Set at midrange

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P29

MAX1253BEUE+

Mfr. #:

Buy MAX1253BEUE+

Manufacturer:

Maxim Integrated

Description:

Analog to Digital Converters - ADC 12-Bit 10Ch 94ksps 3.3V Precision ADC

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MAX1253BEUE+

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