MAX1233_05 Datasheet, PDF (41/45 Pages) Maxim Integrated Products – ±15kV ESD-Protected Touch-Screen Controllers Include DAC and Keypad Controller

±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
MAX1233
MAX1234
AV_DD
DAC
FEEDBACK
RESISTORS
DACOUT
R3
R1 i₁
i₃
R2 i2
V_BATT
SIMPLIFIED DC/DC CONVERTER
ERROR AMP
V_REF
1.25V
CONTROL
V_OUT
(LCD BIAS)
MAX1677
Figure 27. LCD Contrast Control Circuit
CS
SCK
MISO
SPI
V_DD
MOSI
SS
CS
DCLK
DOUT
MAX1233
MAX1234
DIN
BUSY
PENIRQ
KEYIRQ
Figure 28a. SPI Interface
Equation 5 shows that the maximum output voltage occurs
for the minimum DAC voltage, and that the minimum
output voltage occurs for the maximum DAC voltage.
To ensure that the desired output swing is achieved,
choose appropriate values of R1, R2, and R3.
Calculate V_OUTMAX using the following equation:
V_OUTMAX = V_REFMAX + (R1_MAX / R2_MIN)V_REFMAX
+ (R1_MAX / R3_MIN) (V_REFMAX - V_DACMIN)
[Equation 6]
If V_OUTMAX exceeds the maximum ratings of the
LCD/TFT display, the DAC codes that cause the output
voltage to go too high must be avoided.
CS
SCK
MISO
MICROWIRE
MOSI
CS
DCLK
DOUT
MAX1233
MAX1234
DIN
BUSY
PENIRQ
KEYIRQ
Figure 28b. MICROWIRE Interface
Calculate V_OUTMIN using the following equation:
V_OUTMIN= V_REFMIN + (R1_MIN / R2_MAX)V_REFMIN +
(R1_MAX / R3_MIN) (V_REFMIN - V_DACMAX)
[Equation 7]
If V_OUTMIN is too low for desired operation, avoid the DAC
codes, which cause the output voltage to go too low.
Connection to Standard Interface
SPI and MICROWIRE Interfaces
When using an SPI interface (Figure 28a) or
MICROWIRE (Figure 28b), set the CPOL = CPHA = 0.
At least four 8-bit operations are necessary to read or
write data to/from the MAX1233/MAX1234. DOUT data
transitions on the serial clock’s falling edge and is
clocked into the µP on the DCLK’s rising edge. The first
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