Maxim Integrated MAXQ7666 - Manual (Page 99)

When ADCMX4 is cleared, the ADC input channel is configured for a differential voltage measurement. When ADCMX0 is set, the ADC’s
positive and negative inputs are internally connected to the same analog input pin so the user can measure zero offset error, if any.
When ADCMX4 is set, the ADC input channel is configured to measure remote or internal temperature, and the bits ADCMX3:ADCMX0
control the temperature measurement.
The bits ADCMX1 and ADCMX2 determine if internal or external temperature sense mode is selected.
The bits ADCMX0 and ADCMX3 determine the state of the temperature sensor when measuring temperature.
ADCMX0: TS Auto-Zero Control. This bit puts the temperature sensor in auto-zero state when it is set to logic 1. The auto-zero-
ing is used to cancel internal offset effects.
ADCMX3: TS Current Control. This bit sets the temperature sensor current to its high value when set to logic 1, and sets the cur-
rent to its low value when cleared to logic 0.
The ADC performs temperature measurement by measuring the voltage across a diode-connected transistor at two different current
levels.
Note: The temperature measurement process is fully automated in the MAXQ7665/MAXQ7666 ROM utility routine "tempConv." All the
required setup and temperature measurement algorithm steps for both internal and external temperature measurements are handled
in the utility routine and it returns the local or remote temperature result.
Bit 10: Differential Input (ADCDIF). The ADC operates only on differential inputs and this bit must be set to logic 1 if the remote or
internal temperature sensor drive circuit is not selected. For the remote temperature sensor, this bit determines if the input is single-
ended or differential. When this bit is set to logic 1, the remote temperature sense-diode anode connects to the designated positive
input, and cathode connects to the designated negative input. When this bit is cleared to 0, the sense-diode cathode connects to
AGND. If using internal temperature sense mode, leave this bit as 0.
Bit 9: ADC Bipolar Mode Select (ADCBIP). When this bit is set to logic 1, the ADC is in bipolar mode. When this bit is cleared to 0,
the ADC is in unipolar mode.
Bits 8, 7, 5: Reserved. Read returns 0, write ignored.
Bit 6: ADC Dual-Mode Select (ADCDUL). This bit determines the ADC’s acquisition time. When ADCDUL is set to 1, the ADC operates in
dual-edge mode. The rising edge of ADC_CNVST (internal signal formed by a combination of all three conversion start sources described
below) causes the ADC to power up and begin acquisition; the falling edge causes it to sample and perform a conversion. When ADC-
DUL is 0, the ADC operates in single-edge mode. The rising edge controls the entire conversion, i.e., power-up, acquisition, and conver-
sion sequence if the ADC was off; if the ADC was on, it stays in acquisition mode until the rising edge and then starts conversion.
Note: Setting ADCDUL = 1 and PGA gain = 1 is illegal. If ADCDUL is set as 1, make sure the PGA gain (selected by the PGG2:PGG0
bits in the APE register) is greater than 1.
Bit 4: ADC Auto Shutdown (ADCASD). Setting this bit to logic 1 shuts down the ADC automatically after the conversion is complet-
ed. Clearing this bit to 0 disables the auto shutdown function, and leaves the ADC powered on.
Bit 3: ADC Start/Busy (ADCBY). Setting this bit to logic 1 enables the ADC to perform a conversion when ADCS2:ADCS0 is also set
to 111. ADCBY remains set while the conversion is in progress. A read of this bit reflects the busy status of the ADC. ADCBY is cleared
by hardware when the conversion is complete and the data is ready. Attempting to change ADCBY from 1 to 0 by software is blocked
by hardware in order to allow the conversion to complete.
Note that if software-controlled conversions are implemented (by setting ADCS2:ADCS0 to 111) when ADCDUL is also set, then to com-
plete a conversion the user must first write ADCBY to 1 and then write a second time to attempt to set it back to 0. Setting ADCBY to
1 puts the ADC into acquisition mode. The second write attempting to set ADCBY back to 0 moves the ADC from acquisition to the
conversion phase. The second write will not affect the value of ADCBY until the ADC cycle has completed.
MAXQ7665/MAXQ7666 User’s Guide
3-9
ADCMX2 ADCMX1 FUNCTION
0 0 Internal diode-connected transistor based temperature measurement
0 1 Remote diode-connected transistor based temperature measurement on AIN0
1 0 Remote diode-connected transistor based temperature measurement on AIN2
1 1 Reserved
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