MAX1492 Datasheet, PDF (13/35 Pages) Maxim Integrated Products – 3.5- and 4.5-Digit, Single-Chip ADCs with LCD Drivers

3.5- and 4.5-Digit, Single-Chip ADCs
with LCD Drivers
HOLD
PEAK
LOW BATT
BP1
BP2
Figure 6. Backplane Connection for the MAX1492 (3.5 Digits)
SEG10: PEAK, HOLD, BC4
HOLD
PEAK
LOW BATT
BP3
SEG2: A1, G1, D1
ANNUNCIATOR
SEG9: F3, E3, DP3
SEG8: A3, G3, D3
SEG1: B1, C1, N.C.
SEG3: F1, E1, DP1
SEG4: A2, G2, LOWBATT
SEG5: A2, G2, D2
SEG6: F2, E2, DP2
SEG7: B3, C3, MINUS
Figure 7. Segment Connection for the MAX1492 (3.5 Digits)
thus the contrast of the segment. The RMS OFF voltage
is always V_LCD / 3, whereas the RMS ON voltage is
always 1.92V_LCD / 3. This is illustrated in Figure 11. The
ratio of RMS ON to RMS OFF voltage is fixed at 1.92 for
a triplexed LCD.
Figure 12 illustrates contrast vs. applied RMS voltage
with a V_LCD of 3.1V. The RMS ON voltage is 2.1V, and
the RMS OFF voltage is 1.1V. The OFF segment has a
contrast of less than 5%, while the ON segments have
greater than 85% contrast.
If ghosting is present on the LCD, the RMS OFF voltage
is too high. Choose an LCD with a higher RMS OFF
voltage. Alternatively, lower the supply or apply a volt-
age on V_DISP to lower the RMS OFF voltage.
Figures 9 and 10 show the voltage on the LCD’s BP_
inputs and the segment inputs during normal operation.
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