MAX1620 Datasheet, PDF (11/20 Pages) Maxim Integrated Products – Digitally Adjustable LCD Bias Supplies

Digitally Adjustable LCD Bias Supplies
2V
TO
15V
3V
TO
C1
5.5V
0.1µF
C2
0.1µF
R8
10k
D3 1N6263 (ANY SCHOTTKY)
TO REF
3
5 ^BATT
U1
14
LX ₁₆
11 ^POK
DHI ₁₅
7 ^VDD
4 ^POL
MAX1620
MAX1621
DLO ₁₃
PGND
1 ^{SHDN (SUS)}
10
DN (SDA)
2
DOUT ₉
UP (SCL)
6
FB
REF
12 _AGND
8
LCDON
C3
22µF
R3
300k
( ) ARE FOR MAX1621.
NOTE: CONNECTIONS TO DIGITAL INPUTS NOT SHOWN.
Figure 5. Typical Operating Circuit—Negative Output
2V
TO
12V
3V
TO
C1
5.5V
0.1µF
C2
0.1µF
R8
10k
D3 1N6263 (ANY SCHOTTKY)
TO REF
3
5 ^BATT
U1
14
LX ₁₆
11 ^POK
DHI ₁₅
7 ^VDD
4 ^POL
MAX1620
MAX1621
DLO ₁₃
PGND
1 ^{SHDN (SUS)}
10
2 ^{DN (SDA)}
DOUT ₉
6 ^{UP (SCL)}
FB
REF
12 _AGND
8
LCDON
C3
22µF
R3
300k
( ) ARE FOR MAX1621.
NOTE: CONNECTIONS TO DIGITAL INPUTS NOT SHOWN.
Figure 6. Alternative Negative Output—Maximum Voltage
L1
100µH
D1
MBRS0540
C4
1µF
N1
MMFT3055VL
D2
C5
MBRS0540
22µF
R5
1.2M
R4
300k
C6
100pF
L1
100µH
D2
MBRS0540
C4
2.2µF
D1
MBRS0540
C5
22µF
N1
MMFT3055VL
R5
2.7M
R4
300k
C6
100pF
-6V
TO
-12V OUT
-13.5V
TO
-27V OUT
maximum switching frequency. The following equation
represents the output current for the ideal case (no
power losses) of Figure 5:
I_OUT
=
1
2
x (k - factor / L) x V_BATT / (V_BATT + V_OUT)
This means that a higher peak current is required to
achieve the same output current in the negative output
circuit as in the positive output circuit.
The output current for Figure 6 uses the same current
equation as the positive boost.
Output Voltage Control
The output voltage is set with a voltage divider to the
feedback pin (FB). For a positive output, the divider is
referred to GND; for a negative output, the divider is
referred to REF.
Output voltage can be adjusted with an internal DAC
summing current into FB through an external resistor.
The 5-bit DAC is controlled with a user-programmable
up/down counter. On power-up or after a reset, the
counter sets the DAC output to 10000 binary, or half-
scale.
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