MAX1677EEE Maxim Integrated Products, MAX1677EEE Datasheet - Page 13

• Manufacturer Part Number: MAX1677EEE
• Description: IC CONV DC-DC STEP-UP 16-QSOP
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1677EEE

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 3.3V or Adj Main, -28 ~ 28 V or Adj Secondary
• Current - Output: 350mA
• Frequency - Switching: 300kHz
• Voltage - Input: 0.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Power - Output: 696mW
• Output Voltage: 2.5 V to 5.5 V
• Output Current: 350 mA
• Input Voltage: 0.7 V to 5.5 V
• Supply Current: 35 uA
• Switching Frequency: 300 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

in the 10kΩ to 200kΩ range and calculate R1 using one
of the following two equations (for positive or negative
output).
For a positive LCD output, connect LCDPOL to OUT as
shown in Figure 2. This sets the threshold at LCDFB to
1.25V. Select R2 and the desired output voltage
(V
For positive LCD output: R1 = R2 [(V
Figure 3 shows the standard circuit for generating a
negative LCD supply. This connection limits V
values between -V
output voltage is required, D2’s cathode can be con-
nected to V
nection permits output voltages from 0 to -
For a negative LCD output voltage, connect LCDPOL to
GND. The feedback threshold voltage of LCDFB is set
to 0. Select R2 and the desired output voltage (V
and calculate R1:
For negative LCD output: R1 = R2 ×
To minimize ripple in the LCD output and prevent sub-
harmonic noise caused by switching pulse grouping, it
may be necessary in some PC board layouts to con-
nect a small capacitor in parallel with R1. For R1 values
in 500kΩ to 2MΩ range, 22pF is usually adequate.
Many LCD bias applications require an adjustable out-
put voltage. In Figure 9, an external control voltage
(generated by a potentiometer, DAC, filtered PWM con-
trol signal, or other source) is coupled to LCDFB
through the resistor R
cuit, for both positive and negative outputs, is given by:
where V
added adjust voltage, as calculated in one of the pre-
ceding two equations. V
configuration, and 0 for the negative configuration.
R
1.25V × R1 / R
Figure 9. Adjusting LCD Output Voltage
ADJ
LCD
), and calculate R1:
V
sets the output adjustment span, which is
OUT
INIT
IN
= V
MAX1677
is the initial output obtained without the
rather than ground. This alternate con-
ADJ
INIT
______________________________________________________________________________________
IN
+ (R1 / R
for either polarity output. Note that
(REF)
Step-Up and LCD Bias DC-DC Converter
GND
ADJ
FB
and -28V. If a smaller negative
Compact, High-Efficiency, Dual-Output
LCDFB
. The output voltage of this cir-
V
LCD
ADJ
R1
is 1.25V for the positive
)(V
R2
LCDFB
R
ADJ

LCD
V
LCD

- V
/ 1.25V) - 1]
28 - V

ADJ
V
/ 1.25V
ADJ
)
LCD
IN
LCD

.
to
),
raising V
while in negative output designs, raising V
es the magnitude of the negative output.
If the application requires LCD output voltages greater
than +28V, use the connection in Figure 10. This circuit
adds one capacitor-diode charge pump stage to
increase the output voltage without increasing the volt-
age stress on the LCDLX pin. The maximum output
voltage of the circuit is +55V and output current is
slightly less than half that available from the standard
circuit in Figure 2. In Figure 10, diodes D1, D2, and D3
should be at least 30V-rated Schottky diodes such as
1N5818 or MBR0530L or equivalent. Capacitors C1
and C2 should also be rated for 30V, while C3 must be
rated for the maximum set output voltage.
The MAX1677’s high switching frequency allows the
use of small surface-mount inductors. The 10µH values
shown in Figures 2 and 3 are recommended for most
applications, although values between 4.7µH and 47µH
are suitable. Smaller inductance values typically offer a
smaller physical size for a given series resistance,
allowing the smallest overall circuit dimensions. Larger
inductance values exhibit higher output current capa-
bility, but larger physical dimensions.
Figure 10. Higher LCD Output Voltage
MAX1677
ADJ
LCDPOL
LCDLX
LCDFB
OUT
lowers V
Applications Information
1
7
12
10
Higher LCD Output Voltages
10µH
L2
V
OUT
IN
R2
65k
R1
2M
D1, D2, D3 = 30V RATED SCHOTTKY DIODES:
MBR0530L OR EQUIVALENT.
in positive output designs,
C1
1µF
30V
Inductor Selection
D1
D2
C2
2.2µF
30V
D3
ADJ
+40V/5mA
(SET TO
NO MORE
THAN 55V)
C3
2.2µF
increas-
13