Rainbow Electronics MAX1848 - Manual (Page 5)

MAX1848
White LED Step-Up Converter in SOT23
_______________________________________________________________________________________ 5
20ms/div
V CTRL TRANSIENT RESPONSE
V CTRL
V OUT
I LED
1.0V
2.0V
6.7V
6.3V
MAX1848 toc10
30mA
15mA
C COMP = 1 µF
Typical Operating Characteristics (continued)
(See Typical Application Circuit, V+ = 3V, I LED = 15mA, L = 33µH, C OUT = 1µF, C COMP = 0.15µF, R SENSE = 5 Ω, CTRL = 1V, 2 LEDs,
T A = +25 °C, unless otherwise noted.)
200ns/div
SWITCHING WAVEFORMS
V LX
I L
V IN_RIPPLE
0
6.5V
61mA
17mA
MAX1848 toc11
V
OUT_RIPPLE
10mV/div
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
7 CS
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 .
8 V+
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.