Datasheet

71M6511/71M6511H
Single-Phase Energy Meter IC
DATA SHEET
NOVEMBER 2010
Page: 80 of 98 © 2005–2010 Teridian Semiconductor Corporation V2.7
A Maxim Integrated Products Brand
Crystal Oscillator
The oscillator drives a standard 32.768 kHz watch crystal. The oscillator has been designed specifically to handle these
crystals and is compatible with their high impedance and limited power handling capability. The oscillator power dissipation is
very low to maximize the lifetime of any battery backup device attached to VBAT.
Board layouts with minimum capacitance from XIN to XOUT will require less battery current. Good layouts will have XIN and
XOUT shielded from each other.
For best rejection of electromagnetic interference, connect the crystal body and the ground terminals of the two
crystal capacitors to GNDD through a ferrite bead. No external resistor should be connected across the crystal,
since the oscillator is self-biasing.
Connecting LCDs
The 71M6511 has a LCD controller on-chip capable of controlling static or multiplexed LCDs. Figure 31 shows the basic
connection for a LCD.
segments
71M6511
LCD
commons
segments
71M6511
LCD
commons
Figure 31: Connecting LCDs
Figure 32 shows how 5V LCDs can be operated even when a 5V supply is not available. Setting the I/O RAM register
LCD_BSTEN to 1 starts the on-chip boost circuitry that will output an AC frequency on the VDRV pin. Using a small coupling
capacitor, two general-purpose diodes and a reservoir capacitor, a 5VDC voltage is generated which can be fed back into the
VLCD pin of the 71M6511. The LCD drivers are enabled with the I/O register LCD_ON; I/O register LCD_FS is used to adjust
contrast, and LCD_MODE selects the operation mode (LCD type).