MAX848/MAX849
1-Cell to 3-Cell, High-Power,
Low-Noise, Step-Up DC-DC Converters
8 _______________________________________________________________________________________
Pin Description
ADC’s Input Channel Selector. Pull low to select AIN1 and drive high to select AIN2.AINSEL9
ADC’s Serial Output. Pulsed output, RZ format. Full scale is f
OSC
/2 (
f
CLK
/2
in external sync mode). The
DATA output is low when V
CLK/SEL
= 0V (PFM mode).
DATA10
External Clock Input/Regulator’s Switching Mode Selector.
CLK/SEL = low: low-power, low-quiescent PFM mode. Delivers 100mW of output power.
CLK/SEL = high: low-noise, high-power PWM mode, switching at a constant frequency (300kHz).
CLK/SEL = driven with external clock: low-noise, high-power, synchronized PWM mode. The internal
oscillator is synchronized to the external clock (200kHz ~ 400kHz). Turning the DC-DC converter on with
V
CLK/SEL
= 0V also serves as a soft-start function, since the peak inductor current is limited to 30% of the
nominal value.
CLK/SEL11
Source of the Internal N-Channel Power MOSFET. Connect to high-current ground path.PGND12
Drain of the Internal N-Channel Power MOSFET and P-Channel Synchronous RectifierLX13
Output Sense Input. The IC is powered from OUT. Bypass to GND with a 0.1µF ceramic capacitor. Connect
OUT to POUT through a 10Ω series resistor.
OUT5
Power-Good Comparator Input. Connect to GND for fixed threshold (V
OUT
x 0.9). To adjust the threshold,
connect to a resistor divider from OUT to GND.
POKIN6
Dual Mode DC-DC Converter Feedback Input. Connect to GND for fixed 3.3V output voltage. Connect to
a resistor divider from OUT to GND to adjust the output voltage. Minimize noise coupling from switching
signals to FB.
FB7
Power-Good Output. This open-drain output is pulled low when the output voltage (V
OUT
) drops below
the internally set threshold (fixed threshold), or when the voltage at POKIN drops below V
REF
(adjustable
threshold).
POK8
Ground. Use for low-current ground paths. Connect to PGND with a short trace.GND4
Reference Output. Bypass with a 0.22µF capacitor to GND.REF3
PIN
ADC’s Channel 2 Input. Analog input voltage range is 0V to 2.5V.AIN22
ADC’s Channel 1 Input. Analog input voltage range is 0.625V to 1.875V.AIN1
1
FUNCTIONNAME
14 POUT
Source of the Internal P-Channel Synchronous Rectifier MOSFET. Connect an external Schottky diode from
LX to POUT. Bypass to PGND with a 0.1µF ceramic capacitor as close to the IC as possible.
15
ON2 OFF Control Input. When ON1 = 0 and ON2 = 1, the IC is off.
16 ON1
ON Control Input. When ON1 = 1 or ON2 = 0, the IC is on.
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