Rainbow Electronics DS1870 - Manual (Page 11)

DS1870
LDMOS RF Power-Amplifier Bias
Controller
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Temperature-Monitor Operation
The internal temperature monitor values are stored as
16-bit 2’s complement numbers at memory addresses
60h to 61h. The round-robin update time (t
frame ) for the
temperature register is the same as the voltage moni-
tors. The factory default calibration values for the tem-
perature monitor are shown in Table 3.
To convert the 2’s complement register value to the
temperature it represents, first convert the 2-byte hexa-
decimal value to a decimal value as if it is an unsigned
value, then divide the result by 256. Finally, subtract
256 if the result of the division is greater than or equal
to +128. Table 4 shows example converted values.
The offset of the temperature sensor can be adjusted
using the internal calibration registers to account for
differences between the ambient temperature at the
location of the DS1870 and the temperature of the
device it is biasing. When offsets are applied to the
temperature measurement, the value converted will be
off by a fixed value from the DS1870’s ambient temper-
ature. For more information, see the Temperature
Monitor Offset Calibration section.
Potentiometer Operation
Both of the DS1870’s potentiometers are 256 positions
with their high terminals connected to the high common
pin, H
COM . The low terminals of the potentiometers are
internally shunted to GND by resistors such that the
output voltage is 3V to 5V when H
COM is connected to
a 5V source. The internal shunt resistors and the poten-
tiometer’s end-to-end resistance feature matching tem-
perature coefficients that prevent the output voltage
from drifting over temperature.
External resistors can be placed from H COM to L X and/or
from L X to GND to modify the typical output voltage.
Normal Operation
During normal operation, each potentiometer’s position
is automatically adjusted to the sum of its temperature
and drain LUT values after each round of conversions.
The potentiometer setting is applied after both the base
and offset LUT values are recalled from memory. The
sum of the currently indexed values in the POT1 Temp
LUT (memory table 2) and the POT1 Drain LUT (memo-
ry table 4) control potentiometer 1. The sum of the cur-
rently indexed values in the POT2 Temp LUT (memory
table 3) and the POT2 Drain LUT (memory table 5) con-
trol potentiometer 2. In the event that two table values
are summed and the result is greater than 255 or less
than 0, the potentiometer’s position is set to 255 or 0,
respectively.
SIGNAL
+FS
SIGNAL
+FS
(hex)
-FS
SIGNAL
-FS
(hex)
Temp +127.97°C 7FF8 -128.00°C 8000
Table 3. Internal Temperature-Monitor
Factory Default Calibration
MSB
(bin)
LSB
(bin)
TEMPERATURE
(°C)
01000000 00000000 +64
01000000 00001111 +64.059
01011111 00000000 +95
11110110 00000000 -10
11011000 00000000 -40
Table 4. Temperature Conversion Values
LUT ADDRESS (hex)
CORRESPONDING
TEMPERATURE (°C)
80 ≤ -40°C
81 -38°C
82 -36°C
… …
C6 +100°C
C7 ≥ +102°C
Table 5. LUT Addresses for
Corresponding Temperature Values