xe8802 Semtech Corporation, xe8802 Datasheet - Page 164

• Manufacturer Part Number: xe8802
• Description: Data Acquisition Soc With 16+10 Bit Zoomingadc? Embedded Risc Controller And Lcd Driver
• Manufacturer: Semtech Corporation

Finally, in direct drive, there is no need for intermediate voltages. The configurations of Figure 19-12(a) or Figure
19-13(a) can still be used (depending on the required voltage: 2.4V or 3.6V) but the configurations in Figure
19-12(b) or Figure 19-13(b) can be replaced by the simple schematic of Figure 19-14. The external voltage Vext
may or may not be identical to the circuit supply voltage VBAT.
19.5.4.2
To generate the LCD voltages with an external R-ladder (Figure 19-15), the internal voltage reference and
multiplier/divider block are not used (VgenOff=1 and VgenRefEn=0 in RegVgenCfg0). All other bits in the register
RegVgenCfg0 are unused.
All resistor values are equal and sufficiently small in order to have small LCD voltage impedance. For direct drive,
no resistors are required as shown in Figure 19-14. The voltage Vext can be connected to the circuit supply voltage
VBAT or any other external voltage.
© Semtech 2006
Generating LCD voltages with an external resistor ladder
Figure 19-13: Generation of LCD voltage with external capacitors for 1/2 bias mode.
Figure 19-14. Generation of LCD voltage for direct drive using external voltage.
VgenOff = 0
VgenRefEn = 1
VgenMode = 1
VGEN
1.2V v oltage
ref erence
(a)
LCD driv er
pad_v gen_v 1
pad_v gen_v b
pad_v gen_v 3
pad_v gen_v 2
pad_gen_v a
VgenOff = 1
VgenRefEn = 0
VGEN
XE8802 Sensing Machine Data Acquisition MCU
1.2V voltage
reference
C
C
lcd3
lcd1
C
LCD driver
aux
19-20
pad_v gen_v 1
pad_gen_v 3
pad_gen_v a
pad_gen_v b
VgenOff = 0
VgenMode = 1
VgenRefEn = 0
pad_gen_v 2
with ZoomingADC™ and LCD driver
VGEN
1.2V v oltage
ref erence
(b)
voltage
LCD driv er
Vext
pad_v gen_v 1
pad_v gen_v b
pad_v gen_v 3
pad_v gen_v 2
v oltage
Vext
pad_v gen_v a
C
C
lcd3
lcd1
C
aux
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