71M6533 datasheet(13/132 Pages) MAXIM

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FDS_6533_6534_004

71M6533/G/H and 71M6534/H Data Sheet

Rev 2

CHOP_E[1:0] has four states: positive, reverse, and two toggle states. In the positive state, CHOP_E[1:0]

= 01, CROSS and CHOP_CLK are held low. In the reverse state, CHOP_E[1:0] = 10, CROSS and

CHOP_CLK are held high. In the first toggle state, CHOP_E [1:0] = 00, CROSS is automatically toggled

near the end of each multiplexer frame and an ALT frame is forced during the last multiplexer frame in each

SUM cycle. It is desirable that CROSS take on alternate values during each ALT frame. For this reason,

if CHOP_E[1:0] = 00, CROSS will not toggle at the end of the multiplexer frame immediately preceding the

ALT frame in each accumulation interval.

Figure 3: CROSS Signal with CHOP_E[1:0] = 00

Figure 3 shows CROSS over two accumulation intervals when CHOP_E[1:0] = 00. At the end of the

first interval, CROSS is low, at the end of the second interval, CROSS is high. The offset error for

the two temperature measurements taken during the ALT multiplexer frames will be averaged to zero.

Note that the number of multiplexer frames in an accumulation interval is always even. Operation

with CHOP_E[1:0] = 00 does not require control of the chopping mechanism by the MPU while eliminating

the offset for temperature measurement.

In the second toggle state, CHOP_E[1:0] = 11, no ALT frame is forced during the last multiplexer cycle in

an accumulation interval, and CROSS always toggles near the end of each multiplexer frame.

The internal bias voltage, VBIAS (typically 1.6 V), is used by the ADC as a reference when measuring the

temperature and battery monitor signals.

1.2.6 Temperature Sensor

The 71M6533 and 71M6534 include an on-chip temperature sensor implemented as a bandgap reference.

It is used to determine the die temperature. The MPU may request an alternate multiplexer cycle containing

the temperature sensor output by asserting MUX_ALT.

The primary use of the temperature data is to determine the magnitude of compensation required to offset

the thermal drift in the system (see Section 3.5 Temperature Compensation).

1.2.7 Battery Monitor

The battery voltage is measured by the ADC during alternative multiplexer frames if the BME (Battery

Measure Enable) bit in the I/O RAM is set. While BME is set, an on-chip 45 kΩ load resistor is applied to

the battery and a scaled fraction of the battery voltage is applied to the ADC input. After each alternative

MUX frame, the result of the ADC conversion is available at XRAM address 0x0B. BME is ignored and

assumed zero when system power is not available (V1 < VBIAS). See Section 6.4.5 for details regarding

the ADC LSB size and the conversion accuracy.

1.2.8 AFE Functional Description

The AFE functions as a data acquisition system, controlled by the MPU. The main signals (IA, VA, IB,

VB, etc.) are sampled and the ADC counts obtained are stored in XRAM where they can be accessed by

the CE and, if necessary, by the MPU. Alternate multiplexer cycles are initiated less frequently by the

MPU to gather access to the slow temperature and battery signals.

Figure 4 shows the block diagram of the AFE.

Multiplexerframes

Accumulationinterval n

Accumulationinterval n+1

25192520

Alternative MUX cycle

Multiplexerframes

Alternative MUX cycle

CROSS

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