MAX1253 Datasheet, PDF (25/29 Pages) Maxim Integrated Products – Stand-Alone, 10-Channel, 12-Bit System Monitors with Internal Temperature Sensor and VDD Monitor

Stand-Alone, 10-Channel, 12-Bit System Monitors
with Internal Temperature Sensor and V_DD Monitor
Channel-Enable Register Power-Up/Reset Defaults
At power-on or after a RESET command, the channel-
enable register resets to FF hex, enabling all channels:
the internal temperature sensor, the V_DD monitor, and
AIN0–AIN7.
Input Configuration Register
Power-Up/Reset Defaults
At power-on or after a RESET command, the input con-
figuration register resets to 00 hex, configuring
AIN0–AIN7 for single-ended voltage measurement.
Alarm Register Power-Up/Reset Defaults
At power-on or after a RESET command, the alarm reg-
ister is reset to 000000 hex, indicating that no alarm
condition exists.
Current Data Register Power-Up/Reset Defaults
At power-on or after a RESET command, each chan-
nel’s current data register is reset to 800 hex.
Upper Threshold Register Power-Up/Reset Defaults
At power-on or after a RESET command, each chan-
nel's upper threshold register is reset to FFF hex. This
state effectively disables the upper threshold.
Lower Threshold Register Power-Up/Reset Defaults
At power-on or after a RESET command, each chan-
nel's lower threshold register is reset to 000 hex. This
state effectively disables the lower threshold.
Channel Configuration Register
Power-Up/Reset Defaults
At power-on or after a RESET command, each chan-
nel's configuration register is reset to 000 hex, which
configures the fault bits to cause an alarm to occur on
the first overrange or underrange condition and dis-
ables averaging.
Computing Data Throughput
The MAX1253/MAX1254 throughput rate depends on
the number of enabled channels, their configuration
(temperature or voltage), and the reference mode.
Voltage measurements require 10.6µs (typ) to com-
plete, and temperature measurements require 46µs.
Channel pairs configured for differential measurements
count as only one for throughput computation.
The reference system takes 20µs to power up in refer-
ence mode 00 prior to each temperature measurement,
40µs to power up in reference mode 01 after each sam-
ple wait period (if sample wait time > 80µs), and no
power-up time in reference mode 10.
The sampling period is calculated as follows:
t_sw = (t_pu) + (N_v)t_conv[volt] + (N_t)t_conv[temp] + t_wait
where:
t_sw = all channels scan sampling period
t_pu = reference power-up time
t_conv[volt] = voltage-configured channel conversion time
N_v = number of voltage-configured channels
t_conv[temp] = temperature-configured channel conver-
sion time
N_t = number of temperature-configured channels
t_wait = sample wait time
The terms in the above equation are determined as
shown above by the number of enabled channels, the
input channel configuration (voltage vs. temperature),
the sample wait time, and the reference mode. The fol-
lowing calculation shows a numeric example:
t_sw = 40µs + 8 x 10.6µs + 2 x 46µs + 395µs = 611.8µs
• 40µs is the time required for the reference to power-
up (reference mode = 00) every time the
MAX1253/MAX1254 come out of automatic shut-
down mode after a sample wait period.
• 8 x 10.6µs is the time required for seven channels
configured for voltage measurement and the V_DD
monitor.
• 2 x 46µs is the time required for temperature mea-
surement (46µs for each temperature measurement
(internal or external)).
• 395µs is the sample wait time, set by bits B5, B6, B7
of the setup register (see Tables 7 and 8).
The MAX1253/MAX1254 use an internal clock for all
conversions. The serial interface clock does not affect
conversion time.
Performing eight single-ended remote channels tem-
perature measurements, an internal temperature mea-
surement, and an internal V_DD measurement with a
sample wait time of zero results in an average conver-
sion rate of 24ksps or 2.4ksps per channel.
Performing eight single-ended voltage measurements, an
internal temperature measurement, and an internal V_DD
measurement with sample wait time of zero results in an
average conversion rate of 70ksps or 7ksps per channel.
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