MAX1620EEE+ Maxim Integrated Products, MAX1620EEE+ Datasheet - Page 16

• Manufacturer Part Number: MAX1620EEE+
• Description: IC LCD BIAS SUPP DGTL ADJ 16QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1620EEE+

• Applications: LCD Display
• Current - Supply: 150µA
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Output Current: 0.07 A
• Input Voltage: 1.8 V to 20 V
• Switching Frequency: 300 KHz
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Digitally Adjustable LCD Bias Supplies
The DAC is adjustable from 0V to 1.5V in 32 steps, and
1LSB = 1.5V / 31. DAC adjustment of V
by adding R3 to the divider circuit (Figure 4). Be sure
that V
For V
mined as follows:
The general form for V
put (V
At power-up the DAC resets to mid-scale (10000), which
corresponds to V
voltage after reset is as follows:
Note that for a positive output voltage, V
as V
= 0V, and V
For a negative output voltage, V
(V
V
as follows:
Note that for a negative output voltage, V
as V
= 1.5V, and V
The output can be adjusted with a potentiometer instead
of the DAC. Choose R
between REF and GND. Connect R3 to the potentiome-
ter’s wiper, instead of to DOUT. The same design equa-
tions as above apply.
16
R3 = R5 x (V
OUT,MIN
FB
V
DOUT
DOUT
= 2.5MΩ x (0 - 1.5) / (-25 - -12.5) = 300kΩ
______________________________________________________________________________________
OUT,MAX
- V
OUT,RESET
OUT,MAX
DOUT
V
V
OUT,RESET
OUT
DOUT
R3 = R5 x (V
= -12.5V; then determine R3 and V
increases. V
decreases. V
= 2.2MΩ x (1.5) / (25 - 12.5) = 264kΩ
) is:
OUT,MIN
= V
) x R5 / R3. Assume V
FB
= 25V and V
OUT,MIN
does not exceed the LCD panel rating.
OUT,MIN
= V
- V
Setting the Maximum Output Voltage
DOUT
= -12.5 + (0 - 0.774) x (2.5M) /
DOUT,MAX
OUT,MIN
corresponds to V
FB
(300k) = -18.95V
OUT
) / (V
OUT,MAX
OUT,MAX
= 0.774V; therefore, the output
+ (V
corresponds to V
POT
OUT,MIN
as a function of the DAC out-
OUT,MAX
FB
+ (1.5 - 0.774) x R5 / R3
Potentiometer Adjustment
) / (V
= 100kΩ, and connect it
- V
corresponds to V
OUT,MAX
corresponds to V
DOUT
OUT,MAX
= 12.5V, R3 is deter-
OUT
- V
(DAC Adjustment)
DOUT
OUT,MIN
) x R5 / R3
OUT
OUT
= V
DOUT
OUT
= 1.5V.
- V
is provided
= -25V and
OUT,MIN
OUT,RESET
OUT,MIN
increases
increases
= 0V.
)
DOUT
DOUT
)
+
When voltage at POK is greater than 1V, the open-drain
LCDON output pulls low. LCDON withstands 27V; there-
fore, it can drive a PFET or PNP transistor to switch on
the MAX1620/MAX1621’s positive output. The following
represent three cases for using this feature:
1) As an off switch, to ensure that a positive boosted
2) As an output sensing cutoff for positive outputs.
3) As an input sensing output cutoff for positive out-
To control the open-drain output LCDON by sensing
the input voltage, connect a resistor-divider (R1-R2,
Figure 4) from V
example, if the minimum battery voltage is 5.3V, deter-
mine R1 as follows:
LCDON can also be controlled via software (MAX1621,
Table 4).
Table 4. MAX1621 LCDON Output
Truth Table
output goes to 0V during shutdown. In this case,
connect POK to SHDN. Without this switch, the posi-
tive output falls to one diode-drop below the input
voltage (V
for negative outputs, which will fall to 0V in shut-
down anyway.
Connect POK to the feedback voltage divider to
sense the output voltage. The output is switched on
only when it reaches a set percentage of the set
voltage.
puts. Connect POK to a voltage divider to sense the
input voltage. The output is switched on only when
the input reaches the set level (Figure 4).
POK Pin
<1V
<1V
>1V
>1V
R1 = R2 x [(V
BATT
= 100k x [(5.3 / 0.992) - 1] = 434kΩ
BATT
) in shutdown. LCDON is not needed
to POK. Choose R2 = 100k. For
Controlling the LCD Using
LCDON Bit
BATT
0
1
0
1
/ V
POK
POK and
) - 1]
LCDON Output
ON, pulls low
Floating
Floating
Floating
LCDON