Applications information – Rainbow Electronics MAX1730 User Manual
Page 7
To maximize efficiency, the MAX1730 automatically
switches between charge-pump configurations (Figures
1, 2, and 3). Efficiency is greatest when the IN/OUT volt-
age ratio is close to the voltage ratio of the selected
capacitor configuration and decreases for output volt-
ages lower than the divider ratio. To choose between
configurations, the MAX1730 senses the input voltage
and the output voltage. The MAX1730 uses a control
scheme with hysteresis to prevent oscillation between
capacitor configurations.
Applications Information
Setting the Output Voltage
For an output voltage of 1.8V, connect FB to GND. For
an output voltage of 1.9V, connect FB to IN.
MAX1730
50mA Regulated Step-Down Charge Pump
for 1.8V or 1.9V Logic
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7
NOTE: SWITCH STATES SET FOR STAGE 1.
ALL SWITCHES REVERSE STATE FOR STAGE 2.
C
IN
V
IN
C
OUT
C1
C2
V
OUT
= V
IN
Figure 1. 1:1 Capacitor Configuration
VIN
C
IN
C1
C2
C
OUT
V
OUT
= V
IN
2
3
NOTE: SWITCH STATES SET FOR STAGE 1.
ALL SWITCHES REVERSE STATE FOR STAGE 2.
Figure 2. 3:2 Capacitor Configuration
VIN
C
IN
C1
C2
C
OUT
V
OUT
= V
IN
1
2
NOTE: SWITCH STATES SET FOR STAGE 1.
ALL SWITCHES REVERSE STATE FOR STAGE 2.
Figure 3. 2:1 Capacitor Configuration