MAX1674-MAX1676 Maxim, MAX1674-MAX1676 Datasheet - Page 9

• Manufacturer Part Number: MAX1674-MAX1676
• Description: High-Efficiency / Low-Supply-Current / Compact / Step-Up DC-DC Converters
• Manufacturer: Maxim

V
pin to GND (5V) or OUT (3.3V) (Figures 5 and 6).
To adjust the output voltage, connect a resistor-divider
from V
less than 260kΩ for R6. Use the following equation to
calculate R5:
Figure 6. Preset Output Voltage of +5V
Figure 5. Preset Output Voltage of +3.3V
OUT
R3
R4
R3
R4
0.1 F
0.1 F
can be set to 3.3V or 5.5V by connecting the FB
200
OUT
200
R1
R1
to FB to GND (Figure 7). Choose a value
BATT
(MAX1676)
LBI
REF
BATT
(MAX1676)
LBI
REF
R5 = R6 [(V
MAX1674
MAX1675
MAX1676
MAX1674
MAX1675
MAX1676
Selecting the Output Voltage
_______________________________________________________________________________________
GND
GND
(MAX1676)
(MAX1676)
CLSEL
CLSEL
SHDN
SHDN
OUT
OUT
LBO
OUT
LBO
LX
FB
Compact, Step-Up DC-DC Converters
LX
FB
High-Efficiency, Low-Supply-Current,
47 F
47 F
10V
/ V
REF
0.1 F
R2
100k
0.1 F
R2
100k
) - 1]
V
V
IN
LOW-BATTERY
IN
22 H
OUTPUT
22 H
V
OUT
47 F
47 F
LOW-
BATTERY
OUTPUT
OUTPUT
5.0V,
150mA
+3.3V
200mA
where V
5V. The input bias current of FB has a maximum value
of 50nA which allows large-value resistors (R6 ≤ 260kΩ)
to be used.
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:
for V
detector output goes low, and V
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
Figure 7. Setting an Adjustable Output
R3
R4
0.1 F
TRIP
200
R1
REF
≥ 1.3V. V
BATT
(MAX1676)
LBI
REF
= +1.3V and V
R3 = R4 [(V
MAX1674
MAX1675
MAX1676
GND
TRIP
(MAX1676)
CLSEL
SHDN
OUT
LBO
is the level where the low-battery
LX
FB
47 F
TRIP
Low-Battery Detection
OUT
/ V
R2
100k
may range from 2V to
REF
V
REF
IN
) - 1]
0.1 F
R5
R6
22 H
is the internal
LOW-
BATTERY
OUTPUT
47 F
OUTPUT
2V to 5.5V
9