Rainbow Electronics MAX11008 - Manual (Page 34)

MAX11008
high until the current scan is complete and the ADC
sequence halts. In single-conversion mode (CKSEL1,
CKSEL0 = 11), the BUSY signal remains high until the
ADC has completed the current conversion (not the
entire scan), the data has been moved into the FIFO,
and the alarm limits for the channel have been checked
(if alarm is enabled).
Alarm Function
The MAX11008 features a multipurpose alarm function
that indicates when a temperature sensor or a current-
sense amplifier reading exceeds the threshold values
specified in the High Temperature Threshold, Low
Temperature Threshold, High Current Threshold, and
Low Current Threshold registers (see Tables 7 to 10).
The thresholds for each temperature sensor and cur-
rent-sense amplifier channel are set individually and
can be configured to operate in window mode or hys-
teresis mode (see the
Window Mode and Hysteresis
Mode sections). Alarm indication is provided by the
ALARM output while information on the source of the
alarm is contained in the Flag register (see Table 26).
The enabling of the various alarms, the polarity of the
ALARM output (active-high or active-low), the ALARM-
output modes, the alarm-threshold modes, and the
methods by which the MAX11008 services an alarm are
controlled with the Alarm Software Configuration regis-
ter and Alarm Hardware Configuration register (see
Tables 12 and 14).
ALARM-Output Modes
The ALARM output operates in comparator mode or
interrupt mode based on the setting of the ACOMP bit
(D8) in the Alarm Hardware Configuration register (see
Table 14).
When configured for comparator mode, the ALARM
output is asserted when the measured current or tem-
perature value exceeds the set threshold level and is
deasserted when the value returns below the set
threshold level.
When configured for interrupt mode, the ALARM output
is asserted when the measured current/temperature
value exceeds the set threshold level and remains
asserted until the Flag register is read, at which time
the ALARM output is deasserted. The alarm output is
only asserted again if the alarm channel recovers and
then re-trips (or if a different alarm channel trips).
See Figures 19 and 20 for examples of both ALARM-
output modes.
Window Mode
Set the TWIN1 bit (D2) or TWIN2 bit (D6) to 1 in the
Alarm Software Configuration register (see Table 12) to
configure the temperature alarm thresholds for channel 1
or channel 2 to window mode. Set the IWIN1 bit (D0) or
IWIN2 bit (D4) to 1 in the Alarm Software Configuration
register to set the current alarm thresholds for channel 1
or channel 2 to window mode. In window mode, temper-
ature/current measurements are compared to the set
temperature/current high and low thresholds. If a mea-
sured value is outside the configured window values
(between the set high and low thresholds) and that cor-
responding channel is configured to cause an alarm
condition, the alarm asserts. The alarm remains internally
asserted until the measured values from that channel fall
back into the window and past the configurable hystere-
sis. The external behavior of ALARM and the gate
clamps are controlled by the settings of the ACOMP and
ALMCLMP_ bits in the Alarm Hardware Configuration
register. The amount of built-in hysteresis can be varied
from 8 LSBs to 64 LSBs by setting ALMHYST[1:0] bits
(D6 and D7) in the Alarm Hardware Configuration regis-
ter (see Tables 14 and 14a). See Figures 19 and 20 for
window-mode threshold examples.
Hysteresis Mode
Set the TWIN1 bit (D2) or TWIN2 bit (D6) to 0 in the
Alarm Software Configuration register (see Table 12) to
set the temperature alarm thresholds for channel 1 or
channel 2 to hysteresis mode. Set the IWIN1 bit (D0) or
IWIN2 bit (D4) to 0 to set the current alarm thresholds
for channel 1 or channel 2 to hysteresis mode. In hys-
teresis mode, temperature or current measurements
are compared to the set temperature/current high and
low thresholds. If a measured value is above the set
high threshold and the corresponding channel is con-
figured to cause an alarm condition, the alarm asserts.
ALARM remains internally asserted until the measured
values from that channel fall back below the low thresh-
old setting. The external behavior of ALARM and the
gate clamps are controlled by the settings of the
ACOMP and ALMCLMP_ bits in the Alarm Hardware
Configuration register. See Figures 21 and 22 for hys-
teresis-mode threshold examples.
V GATE _ Output Equation
Based on the monitored LDMOS current analog input
voltage and temperature values, the MAX11008 logically
decides if the calculated bias voltage, V
GATE_ , driving the
gate of the RF LDMOS, should be recalculated and
adjusted to maintain the desired RF LDMOS drain cur-
rent. The MAX11008 independently monitors and calcu-
lates the V
GATE_
voltage for both channel 1 and channel
2. The MAX11008 implements the following equation
when calculating V
GATE_ for each DAC channel:
Dual RF LDMOS Bias Controller with
Nonvolatile Memory
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