MAX1795 Ver la hoja de datos (PDF) - Maxim Integrated
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MAX1795 Datasheet PDF : 13 Pages
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MAX1795/MAX1796/
MAX1797
Low-Supply Current, Step-Up DC-DC Converters
with True Shutdown
VIN
MAX1795
MAX1796
MAX1797
BATT
R1
200Ω
DAMPING
SWITCH
LX
OUT
22µH
VOUT
47µF
Figure 3. Simplified Diagram of Inductor Damping Switch
VLX
1V/div
2µs/div
Figure 4. LX Ringing for Conventional Step-Up Converter
(without Damping Switch)
VLX
1V/div
2µs/div
Figure 5. LX Waveform with Damping Switch
path to quickly dissipate this energy, minimizing the ringing
at LX. Damping LX ringing does not reduce VOUT ripple,
but does reduce EMI (Figure 3, Figure 4, and Figure 5).
Setting the Output Voltage
VOUT can be set to 3.3V or 5.0V by connecting the FB
pin to GND (5V) or OUT (3.3V). To adjust the output
voltage, connect a resistive voltage-divider from OUT to
FB to GND (Figure 6). Choose a value less than 250kΩ
for R2.
VIN
47µF
BATT
LX
R3
OUT
LBI
SHDN
1M
R4
MAX1795
MAX1796
R1
MAX1797
LBO
FB
GND
R2
OUTPUT
2V TO 5.5V
47µF
LOW-BATTERY
OUTPUT
Figure 6. Setting an Adjustable Output
Use the following equation to calculate R1:
R1 = R2 [(VOUT/VFB) - 1]
where VFB = +1.245V, and VOUT can range from +2V to
+5.5V.
Low-Battery Detection
The MAX1795/MAX1796/MAX1797 each contain an on-
chip comparator for low-battery detection. If the voltage
at LBI is above 0.85V, LBO (an open-drain output) sinks
current to GND. If the voltage at LBI is below 0.85V, LBO
goes high impedance. The LBI/LBO function remains
active even when the part is in shutdown.
Connect a resistive voltage-divider to LBI from BATT to
GND. The low-battery monitor threshold is set by two
resistors, R3 and R4 (Figure 6). Since the LBI bias current
is typically 2nA, large resistor values (R4 up to 250kΩ)
can be used to minimize loading of the input supply.
Calculate R3 using the following equation:
R3 = R4[(VTRIP/0.85V) - 1]
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