Rainbow Electronics MAX849 - Manual (Page 8)

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. AINSEL 9
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).
DATA 10
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/SEL 11
Source of the Internal N-Channel Power MOSFET. Connect to high-current ground path. PGND 12
Drain of the Internal N-Channel Power MOSFET and P-Channel Synchronous Rectifier LX 13
Output Sense Input. The IC is powered from OUT. Bypass to GND with a 0.1µF ceramic capacitor. Connect
OUT to POUT through a 10
Ω
series resistor.
OUT 5
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.
POKIN 6
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.
FB 7
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).
POK 8
Ground. Use for low-current ground paths. Connect to PGND with a short trace. GND 4
Reference Output. Bypass with a 0.22µF capacitor to GND. REF 3
PIN
ADC’s Channel 2 Input. Analog input voltage range is 0V to 2.5V. AIN2 2
ADC’s Channel 1 Input. Analog input voltage range is 0.625V to 1.875V. AIN1 1
FUNCTION NAME
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.