Datasheet

MAX1709
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
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Pin Description
PIN
TSSOP NARROW SO NAME FUNCTION
1 1 ONA
On-Control Input. When ONA = high OR ONB = low, the device turns on
2–8 2, 3, 4 LX
Drain of n-Channel Power Switch. Connect pins 2, 3, and 4 together.
Connect external Schottky diode from LX to OUT.
11, 14 5, 8 GND Ground. Connect ground inputs together, then connect to PGND.
12 6 SS/LIM
Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to
GND to control the rate at which the device reaches current limit (soft-start).
To reduce the current limit from the preset values, connect a resistor from
SS/LIM to GND (see Design Procedure). During shutdown, this pin is
internally pulled to GND to discharge the soft-start capacitor.
13 7 REF
1.26V Voltage Reference Output. Bypass with a 0.22µF capacitor to GND.
Maximum REF load is 50µA.
15 9 OUT
Output Voltage Sense Input. The device is powered from OUT. Bypass with
a 0.1µF to PGND with less than 5mm trace length. Connect a 2Ω series
resistor from the output filter capacitor to OUT (Figure 1).
16 10 FB
DC-DC Converter Feedback Input. Connect FB to GND for internally set
output voltage (see 3.3/5 pin description). Connect a resistor-divider from
the output to set the output voltage in the +2.5V to +5.5V range. FB
regulates to +1.25V (Figure 4).
18–23 11, 12, 13 PGND
Power Ground. Source of n-channel power MOSFET switch. Connect PGND
inputs together, then connect to GND.
26 14 3.3/5
Output Voltage Selection Pin. When FB is connected to GND, the regulator
uses internal feedback to set the output voltage. 3.3/5 = low sets output to
3.3V; 3.3/5 = high sets output to 5V. If an external divider is used at FB,
connect 3.3/5 to ground.
27 15 CLK
Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator.
Optionally, drive with an external clock for external synchronization.
28
16 ONB
Shutdown Input. When ONB = high AND ONA = low, the device turns off
(Table 1).
9, 10, 17,
24, 25
— N.C. No Connect. Not internally connected.
EP
—EP
Exposed Pad. Connect to large ground plane for maximum thermal
dissipation.