MAX1233_05 Datasheet, PDF (32/45 Pages) Maxim Integrated Products – ±15kV ESD-Protected Touch-Screen Controllers Include DAC and Keypad Controller

±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
Auxiliary Analog Inputs
Two auxiliary analog inputs (AUX1 and AUX2) allow the
MAX1233/MAX1234 to monitor analog input voltages
from zero to V_REF. Figure 16 illustrates the process of
auxiliary input reading.
Temperature Measurements
The MAX1233/MAX1234 provide two temperature mea-
surement options: a single-ended conversion method
and a differential conversion method. Both temperature
measurement techniques rely on the semiconductor
junction’s operational characteristics at a fixed current
level. The forward diode voltage (V_BE) vs. temperature
is a well-defined characteristic. The ambient tempera-
ture can be predicted in applications by knowing the
value of the V_BE voltage at a fixed temperature and then
monitoring the delta of that voltage as the temperature
changes. Figure 17 illustrates the functional block of the
internal temperature sensor.
The single conversion method requires calibration at a
known temperature, but only requires a single reading
to predict the ambient temperature. First, the internal
diode forward bias voltage is measured by the ADC at a
known temperature. Subsequent diode measurements
provide an estimate of the ambient temperature through
extrapolation. This assumes a temperature coefficient of
-2.1mV/°C. The single conversion method results in a
resolution of 0.29°C/LSB (2.5V reference) and
0.12°C/LSB (1.0V reference) with a typical accuracy of
±2°C. Figure 18 shows the flowchart for the single tem-
perature measurement.
The differential conversion method uses two measure-
ment points. The first measurement is performed with a
fixed bias current into the internal diode. The second
measurement is performed with a fixed multiple of the
original bias current. The voltage difference between the
first and second conversion is proportional to the
absolute temperature and is expressed by the following
formula:
∆V_BE = (kT/q) ✕ ln(N)
where:
∆V_BE = difference in diode voltage
N = current ratio of the second measurement to the first
measurement
k = Boltzmann’s constant (1.38 × 10^-23 eV/°Kelvin)
q = electron charge (1.60 × 10^-19 C)
T = temperature in °Kelvin
The resultant equation solving for °K is:
T(°K) = q x ∆V / (k × ln(N))
HOST WRITES
ADC
CONTROL REGISTER
START CLOCK
SET BUSY
LOW
AUXILIARY INPUT 1 OR
AUXILIARY INPUT 2
IS ADC
NO
REFERENCE IN
AUTO POWER-DOWN
MODE?
YES
POWER UP REFERENCE
POWER UP
ADC
CONVERT
AUXILIARY INPUT 1 OR 2
NO
IS DATA
AVERAGING DONE?
YES
STORE AUXILIARY INPUT 1 OR 2 IN
AUX1 OR AUX2 REGISTER
POWER DOWN
ADC
POWER DOWN REFERENCE
SET BUSY HIGH
TURN OFF CLOCK
DONE
Figure 16. Auxiliary Input Flowchart
MUX
A/D
CONVERTER
TEMP1 TEMP2
Figure 17. Internal Block Diagram of Temperature Sensor
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