MAX749ESA Maxim Integrated Products, MAX749ESA Datasheet - Page 7

• Manufacturer Part Number: MAX749ESA
• Description: Display Drivers Digitally Adjustable able LCD Bias Supply
• Manufacturer: Maxim Integrated Products

Figure 3. Shutdown-Reset-On-Shutdown Sequence of Operation.
The device is not shut down during reset.
Figure 4. Count-Up Operation
Figure 5. Reset Sequence without Shutdown. The device is not
shut down during reset.
Figure 6. Reset Sequence with Shutdown
SHUTDOWN RESET
ADJ
CTRL
CTRL
ADJ
CTRL
SHUTDOWN
ADJ
CTRL
ON
ADJ
t
R
t
RS
_______________________________________________________________________________________
t
SH
t
R
RESET
RESET
t
SL
Digitally Adjustable LCD Bias Supply
t
R
ON
t
RH
t
t
RH
SD
ON
SHUTDOWN
HIGH
ON
In Figure 3, the MAX749 is reset when it is taken out of
shutdown, which sets the output at mid-scale. Figure 4
shows how to increment the counter. Figure 5 illustrates
a reset without shutting the device down.
Figure 7 provides an example of a sequence of opera-
tions: Starting from shutdown, the device is turned on,
incremented, reset to mid-scale without being shut
down, incremented again, and finally shut down.
When CTRL and ADJ are both low, the MAX749 is shut
down (Table 1): The internal reference and biasing cir-
cuitry turn off, the output voltage drops to zero, and the
supply current drops to 15µA. The MAX749 retains its
DAC setting, simplifying software control.
If ADJ is high when CTRL is low, the DAC set point is
reset to mid-scale and the MAX749 is not shut down.
Mid-scale is 32 steps from the minimum, 31 steps from
the maximum.
The MAX749’s output voltage is set using an external
resistor and the internal current-output DAC. The full-
scale output voltage is set by selecting the feedback
resistor R
The device is in regulation when V
On power-up or after a reset, the counter sets the DAC
output to mid-range, and -V
rising edge of ADJ increments the counter (and there-
fore the DAC output) in the direction of -V
one count. When incremented beyond -V
Figure 7. Control Sequence Example (see Output Voltage
Control section)
_________and Component Selection
SHUTDOWN
CTRL
ADJ
FB
-V
OUT(MAX)
according to the formula:
INCREMENT
Setting the Output Voltage
= R
FB
RESET
ON
Design Procedure
x 20µA (Figure 1).
OUT
= R
INCREMENT
FB
Shutdown Mode
FB
= 0V.
DAC Adjustment
x 13.33µA. Each
Reset Mode
OUT(MAX)
OUT(MAX)
SHUTDOWN
, the
by
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