71M6534 datasheet(75/132 Pages) MAXIM | Exceeds IEC 62053/ANSI C12.20 Standards

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FDS_6533_6534_004

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

Rev 2

Figure 40: Connection for Optical Components

4.7 Connecting the V1 Pin

A voltage divider should be used to establish that V1 is in a safe range when the meter is in MISSION

mode (see Figure 41). V1 must be lower than 2.9 V in all cases in order to keep the hardware watchdog

timer enabled. The resistor divider ratio must be chosen so that V1 crosses the VBIAS threshold when

V3P3 is near the minimum supply voltage (3.0 VDC). A series resistor (R3) provides additional hysteresis,

and a capacitor to ground (C1) is added for enhanced EMC immunity.

The amount of hysteresis depends on the choice of R1 and R3: If V1 < VBIAS, approximately 1 µA will

flow into the on-chip V1 comparator causing a voltage drop. If V1 ≥ VBIAS, almost no current will flow

into the comparator. The voltage drop will require V3P3 to be slightly higher for V1 to cross the VBIAS

threshold when V3P3 is rising as compared to when V3P3 is falling. Maintaining sufficient hysteresis

helps to eliminate rapid mode changes which may occur in cases where the power supply is unstable with

V1 close to the VBIAS threshold point.

Figure 41: Voltage Divider for V1

4.8

Connecting the Reset Pin

Even though a functional meter will not necessarily need a reset switch, it is useful to have a reset push-

button for prototyping as shown in Figure 42, left side. The RESET signal may be sourced from V3P3SYS

(functional in MISSION mode only), V3P3D (MISSION and BROWNOUT modes), or VBAT (all modes, if

a battery is present), or from a combination of these sources, depending on the application.

For a production meter, the RESET pin should be protected by the by the external components shown in

Figure 42, right side. R1 should be in the range of 100 Ω and mounted as closely as possible to the IC.

Since the 71M6533 and 71M6534 generates its own power-on reset, a reset button or circuitry, as

shown in Figure 42, is only required for test units and prototypes.

V3P3

100pF

GND

16.9kΩ

20kΩ

OPT_TX

OPT_RX

71M6533/71M6534

V3P3SYS

Phototransistor

LED

10 kΩ

100 pF

V3P3SYS

71M6534 Datasheet(PDF) 75 Page - Maxim Integrated Products