Rainbow-electronics MAX1848 Manual de usuario descargar pdf (Pagina 5)

MAX1848

White LED Step-Up Converter in SOT23

_______________________________________________________________________________________ 5

20ms/div

CTRL

TRANSIENT RESPONSE

CTRL

OUT

LED

1.0V

2.0V

6.7V

6.3V

MAX1848 toc10

30mA

15mA

COMP

= 1µF

Typical Operating Characteristics (continued)

(See Typical Application Circuit, V+ = 3V, I

LED

= 15mA, L = 33µH, C

OUT

= 1µF, C

COMP

= 0.15µF, R

SENSE

= 5Ω, CTRL = 1V, 2 LEDs,

= +25°C, unless otherwise noted.)

200ns/div

SWITCHING WAVEFORMS

IN_RIPPLE

6.5V

61mA

17mA

MAX1848 toc11

OUT_RIPPLE

10mV/div

Pin Description

PIN NAME FUNCTION

1 COMP

Compensation Pin for Error Amplifier. Connect capacitor from COMP to GND. Startup time is set

by the capacitance connected to this pin (0.833ms for each 0.01µF). V

COMP

passively

discharges to GND when in shutdown.

2 CTRL

Brightness/Shutdown Dual Mode Control Input. LED brightness and IC shutdown are controlled

by the voltage on CTRL. Voltages between 250mV and 5.5V or (V+ + 2V), whichever is less,

adjust the brightness from dim to bright, respectively. To put the IC into shutdown, drive below

100mV or connect to GND.

3 OUT

Overvoltage Sense. When V

OUT

is greater than 13.25V, the internal N-channel MOSFET is turned

off and V

COMP

decays to GND. When V

OUT

drops below 12.25V, the IC will re-enter soft-start.

Connect a 1µF capacitor from OUT to GND.

4 LX Inductor Connection. Drain of the internal high-voltage N-channel MOSFET.

5 PGND Power Ground. Source of the internal high-voltage N-channel MOSFET.

6 GND Ground

7CS

Current-Sense Feedback Input. Connect a resistor from this pin to GND to set the LED bias

current. This pin regulates to 7.5% of V

CTRL

8V+

Supply Voltage Input. The IC is powered from this pin. Input range is 2.6V to 5.5V. Bypass with a

ceramic capacitor to GND.

1 2 3 4 5 6 7 8 9

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Rainbow-electronics MAX1848 Manual de usuario Pagina 5

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