MAX746CSE データシートの表示（PDF） - Maxim Integrated
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MAX746CSE Datasheet PDF : 16 Pages
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High-Efficiency, PWM, Step-Down,
N-Channel DC-DC Controller
3a. CHARGE-PUMP
VOLTAGE DOUBLER
VIN
15
V+
MAX746
T FLIP-
T FLOP Q
CLK
100kHz
OSCILLATOR
D2
D3
D4
1N914 1N914 1N5817
C8
C9
0.1µF
1µF
CP 14
HIGH 13
5V
AV+
GND
16
VIN
3b. CHARGE-PUMP
VOLTAGE TRIPLER
D4
1N5817
D2 D3
D5
D6
1N914 1N914 1N914 1N914
C8
C9
C10 C11
15
0.1µF 1µF 0.1µF 1µF
V+
CP 14
MAX746 HIGH 13
GND
16
Figure 3. Charge-Pump Configurations
PEAK CURRENT LIMIT
vs. SOFT-START VOLTAGE
3
RSENSE = 50mΩ
2
V+ - VCS = 150mV
1
RSENSE = 100mΩ
0
0
1
2
3
4
SOFT-START VOLTAGE (V)
Figure 4. Peak Current Limit vs. Soft-Start Voltage
VIN
15
V+
…TO VOUT OR VIN
R2
2
LBI
MAX746
LBO 1
R1
R3
100k
LOW-BATTERY
OUTPUT
GND
16
( ) R2 = R1
VTRIP
VREF
-1
VREF = 2.0V
Figure 5. Input Voltage Monitor Circuit
__________________Design Procedure
Setting the Output Voltage
The MAX746’s dual-mode output voltage can be set
to 5V by grounding FB, or it can be adjusted from
2V to 14V using external resistors R4 and R5 config-
ured as shown in Figure 6. Select feedback resistor
R4 in the 10kΩ to 60kΩ range. R5 is given by:
( ) R5 = (R4) __V_O_U__T_ – 1
2V
The MAX746 is designed to use either internal or exter-
nal feedback mode, but should not be toggled between
the two modes while operating. If two different output
voltages are required, use external feedback mode
with a resistor network similar to the 3.3V/5V adjustable
output circuit shown in Figure 7.
Selecting RSENSE
To select the sense-resistor value (RSENSE), first
approximate the peak current assuming IPK is
(1.1) (ILOAD), where ILOAD is the maximum load cur-
rent. Once all component values have been deter-
mined, the actual peak current is given by:
( ) ( ) IPK = ILOAD + ___V__O_U_T____ 1– _V_O__U_T__
(2L) (fOSC)
VIN
______________________________________________________________________________________ 11
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