MAX11008 Datasheet, PDF (29/67 Pages) Maxim Integrated Products – Dual RF LDMOS Bias Controller with Nonvolatile Memory

Dual RF LDMOS Bias Controller with
Nonvolatile Memory
ADC and DAC References
The MAX11008 provides an internal low-noise +2.5V
reference for the ADCs, DACs and temperature sensor.
When using the internal reference the REFDAC and
REFADC inputs can either be left open or to improve
noise performance, bypassed with a 0.1µF capacitor to
AGND. Connect a voltage source to the REFADC input
ranging between +1V to AV_DD to configure the device
for external ADC reference mode. Connect a voltage
source to the REFDAC input ranging between +0.7V to
+2.5V to configure the device for external DAC refer-
ence mode. When using an external voltage reference,
bypass the REFDAC and REFADC inputs with a 0.1µF
capacitor to AGND. Bits D[3:0] within the Hardware
Configuration register control the source of the DAC
and ADC references. See Table 11.
Temperature Sensors
The MAX11008 measures the internal die temperature
and two external LDMOS transistor temperatures through
one internal and two external diode-connected transis-
tors. The MAX11008 performs temperature measure-
ments by changing the bias current of each diode from
4µA to 68µA to produce a temperature-dependent bias
voltage difference. The internal ADC converts the volt-
age difference to a digital value. The conversion result at
4µA is subtracted from the conversion results at 68µA to
calculate a digital value that is proportional to absolute
temperature. The output data sent to the master will be
the resultant digital code minus an offset value to adjust
from Kelvin to Celsius. Temperature data is delivered to
the master as a 12-bit signed (two’s complement) frac-
tional number with the 3 LSBs being the fractional bits.
This provides a temperature measurement resolution of
1/8°C. See Table 3 for examples of the signed fractional
number digital temperature codes.
Table 3. Signed Fractional Number
Temperature-Code Examples
TEMPERATURE
(°C)
-40
-1.625
0
+27.125
+105
DIGITAL CODE
[D11:0]
1110 1100 0000
1111 1111 0011
0000 0000 0000
0000 1101 1001
0011 0100 1000
In clock mode 00, initiate temperature conversions by
writing 0x13 to the ADC Conversion register. In clock
mode 01, initiate temperature conversions by writing
0x13 to the ADC Conversion register and pulse CNVST
low. In clock mode 11, initiate temperature conversions
by writing 0x13 to the ADC Conversion register and
pulse CNVST low for each channel conversion. Set the
corresponding data bits for the temperature sensor to
be measured to 1 (see the ADC Conversion Register
(ADCCON) (Write Only) section and Table 20) for all
three clock modes. Set the high and low external tem-
perature thresholds through the temperature threshold
registers. See the Low Temperature Threshold
Registers (TL1, TL2) (Read/Write) section, High
Temperature Threshold Registers (TH1, TH2)
(Read/Write) section, and Tables 7 and 8).
The reference voltage for the temperature measure-
ments is always derived from the internal reference
source to ensure that 1 LSB corresponds to 1/8 of a
degree Celsius. On every scan where only temperature
measurements are requested, temperature conversions
are carried out in the following order: INTEMP,
EXTEMP1, then EXTEMP2. If the ADCMON bit is set
when the conversions are performed, the temperature
readings are available in the FIFO.
The temperature-sensing circuits power up at the start
of an ADC conversion scan. The temperature-sensing
circuits remain powered on until the end of the scan to
avoid a 50µs delay caused by the internal reference
power-up time required for each individual temperature
channel. The temperature-sensor circuits remain pow-
ered up when the ADC conversion register’s continu-
ous convert bit (CONCONV, see Table 20) is set to 1
and the current ADC conversion includes a tempera-
ture channel. The temperature-sensor circuits remain
powered up until the CONCONV bit is set low.
The external temperature-sensor drive current ratio has
been optimized for a 2N3904 npn transistor with an ide-
ality factor of 1.0065. The nonideality offset is removed
internally by a preset digital coefficient. Using a transis-
tor with a different ideality factor produces a proportion-
ate difference in the absolute measured temperature.
For more details on this topic and others related to
using an external temperature sensor, refer to
Application Note 1057: Compensating for Ideality
Factor and Series Resistance Differences between
Thermal Sense Diodes and Application Note 1944:
Temperature Monitoring Using the MAX1253/54 and
MAX1153/54.
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