71M6521DEIM-DB Maxim Integrated Products, 71M6521DEIM-DB Datasheet - Page 80

• Manufacturer Part Number: 71M6521DEIM-DB
• Description: Power Management Modules & Development Tools 71M6521DE DEMO BOARD M6521DE DEMO BOARD
• Manufacturer: Maxim Integrated Products

Specifications of 71M6521DEIM-DB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The internal voltage reference of the 652X ICs is calibrated during device manufacture. Trim data is stored in on-chip
fuses. The temperature coefficients TC1 and TC2 are given as constants that represent typical component behavior.
The bandgap temperature is provided to the embedded MPU, which then may digitally compensate the power outputs.
This permits a system-wide temperature correction over the entire system rather than local to the chip. The
incorporated thermal coefficients may include the current sensors, the voltage sensors, and other influences. Since the
band gap is chopper stabilized via the CHOP_EN bits, the most significant long-term drift mechanism in the voltage
reference is removed.
The CE applies the gain supplied by the MPU in GAIN_ADJ. This external type of compensation enables the MPU to
control the CE gain based on any variable, and when EXT_TEMP = 15, GAIN_ADJ is an input to the CE.
The flexibility provided by the MPU allows for compensation of the RTC using the substrate temperature. To achieve
this, the crystal has to be characterized over temperature and the three coefficients Y_CAL, Y_CALC, and Y_CAL_C2
have to be calculated. Provided the IC substrate temperatures tracks the crystal temperature the coefficients can be
used in the MPU firmware to trigger occasional corrections of the RTC seconds count, using the RTC_DEC_SEC or
RTC_INC_SEC registers in I/O RAM.
Example: Let us assume a crystal characterized by the measurements shown in Table 5-13.
The values show that even at nominal temperature (the temperature at which the chip was calibrated for energy), the
deviation from the ideal crystal frequency is 11.6 PPM, resulting in about one second inaccuracy per day, i.e. more
than some standards allow. As Figure 5-24 shows, even a constant compensation would not bring much improvement,
since the temperature characteristics of the crystal are a mix of constant, linear, and quadratic effects.
Revision 1.7
5.14.3
5.14.4
Temperature Compensation for Measurements
Temperature Compensation for the RTC
Temperature [°C]
32768.5
32768.4
32768.3
32768.2
32768.1
32767.9
32767.8
32767.7
32767.6
32767.5
Deviation from
32768
© Copyright 2005-2007 TERIDIAN Semiconductor Corporation
Figure 5-24: Crystal Frequency over Temperature
Nominal
-50
+50
+25
-25
-50
0
Table 5-13: Frequency over Temperature
-25
TERIDIAN Proprietary
Frequency [Hz]
Measured
32767.98
32768.28
32768.38
32768.08
32767.58
0
Frequency [PPM]
25
Deviation from
Nominal
-12.817
11.597
8.545
2.441
-0.61
71M652X Software User’s Guide
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