Part No.:
MAX1675EUA
Description:
[High-Efficiency, Low-Supply-Current, Compact, Step-Up DC-DC Converters]
File Size:
162 K
Page:
12 Pages
Logo:
Manufacturer:
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters
Selecting the Output Voltage
V
OUT
can be set to 3.3V or 5.5V by connecting the FB
pin to GND (5V) or OUT (3.3V) (Figures 5 and 6).
To adjust the output voltage, connect a resistor-divider
from V
OUT
to FB to GND (Figure 7). Choose a value
less than 260kΩ for R6. Use the following equation to
calculate R5:
R5 = R6 [(V
OUT
/ V
REF
) - 1]
where V
REF
= +1.3V and V
OUT
may range from 2V to
5V. The input bias current of FB has a maximum value
of 50nA which allows large-value resistors (R6
260kΩ)
to be used.
MAX1674/MAX1675/MAX1676
Low-Battery Detection
The MAX1674/MAX1675/MAX1676 contain an on-chip
comparator for low-battery detection. If the voltage at
LBI falls below the internal reference voltage (1.30V),
LBO
(an open-drain output) sinks current to GND. The
low-battery monitor threshold is set by two resistors, R3
and R4 (Figures 5, 6, and 7). Since the LBI current is
less than 50nA, large resistor values (R4
260kΩ) can
be used to minimize loading of the input supply.
Calculate R3 using the following equation:
R3 = R4 [(V
TRIP
/ V
REF
) - 1]
for V
TRIP
1.3V. V
TRIP
is the level where the low-battery
detector output goes low, and V
REF
is the internal
1.30V reference. Connect a pull-up resistor of 100kΩ or
greater from
LBO
to OUT when driving CMOS circuits.
LBO
is an open-drain output, and can be pulled as
high as 6V regardless of the voltage at OUT. When LBI
is above the threshold, the
LBO
output is high imped-
ance. If the low-battery comparator is not used, ground
V
IN
47µF
10V
R1
200Ω
22µH
BATT
(MAX1676)
LX
OUT
CLSEL
(MAX1676)
FB
SHDN
0.1µF
V
OUT
47µF
+3.3V
200mA
R3
LBI
R4
REF
0.1µF
MAX1674
MAX1675
MAX1676
GND
R2
100k
LBO
LOW-BATTERY
OUTPUT
V
IN
Figure 5. Preset Output Voltage of +3.3V
47µF
V
IN
R1
200Ω
47µF
R1
200Ω
BATT
(MAX1676)
22µH
LX
OUT
SHDN
CLSEL
(MAX1676)
R2
100k
0.1µF
R5
LOW-
BATTERY
OUTPUT
OUTPUT
2V to 5.5V
47µF
22µH
R3
LBI
BATT
(MAX1676)
LX
OUT
CLSEL
(MAX1676)
SHDN
R2
100k
REF
LOW-
BATTERY
OUTPUT
0.1µF
OUTPUT
5.0V,
150mA
47µF
R4
R3
LBI
R4
MAX1674
MAX1675
MAX1676
GND
0.1µF
LBO
FB
REF
0.1µF
MAX1674
MAX1675
MAX1676
GND
LBO
FB
R6
Figure 6. Preset Output Voltage of +5V
Figure 7. Setting an Adjustable Output
9
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