SGM3127 Datasheet, PDF (8/11 Pages) SG Micro Corp – LowDropout CurrentSource

SGM3127
APPLICATION INFORMATION
The SGM3127 is a 4-Channel current source driver for
white LEDs.
Enable Input
EN powers the input of the SGM3127. This IC provides
an under-voltage lockout (UVLO) function to prevent it
from unstable issue when startup. The UVLO threshold of
input falling voltage is set at 2.1V typically with a
hysteresis 0.11V. Drive EN high to enable the device;
drive EN low to disable the device. When driven high, EN
draws 240μA to power the IC. Driving EN low forces
LED1, LED2, LED3, and LED4 into a high-impedance
state.
LED Current
SGM3127 provides a constant current for white LED.
Figure 1 shows a typical application circuit for 4 white
LEDs. Each channel supports up to 30mA current and
regulates a constant current for uniform intensity. For
keypad LED application, the all channels must be
connected to LED as shown in Figure 2. In order to
maintain LED constant current, the input voltage must
provide the required LED forward voltage and current
source dropout voltage. If the forward voltage of white
LEDs is 3.3V, the input voltage should be higher than
3.4V to provide enough voltage headroom for maintaining
constant brightness.
VIN
Keypad
LED
LED1 LED2 LED3 LED4
C_IN
0.1µF
White LED Driver with
Low Dropout Current Source
LED Brightness Dimming Control
For controlling the LED brightness, the SGM3127 can
perform the dimming control by applying a PWM signal to
EN pin. When an external PWM signal is connected to
the EN pin, brightness of white LED is adjusted by the
duty cycle. The average LED current is proportional to
the PWM signal duty cycle. The magnitude of the PWM
signal must be higher than the minimum level of enable
input high level, in order to let the dimming control
perform correctly, the suggested PWM frequency range
is 10kHz to 200Hz.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature 150℃. The
maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junctions and ambient. The maximum power dissipation
can be calculated by following formula:
P_D(MAX) = ( T_J(MAX) - T_A ) / θ_JA
Where T_J(MAX) is the maximum operation junction
temperature 150℃, T_A is the ambient temperature and
the θ_JA is the junction to ambient thermal resistance.
For recommended operating conditions specification of
SGM3127, where T_J(MAX) is the maximum junction
temperature of the die (150°C) and T_A is the maximum
ambient temperature. The junction to ambient thermal
resistance θ_JA is layout dependent. For SOT-23-6
package, the thermal resistance θ_JA is 250℃/W. The
maximum power dissipation at T_A = 25℃ can be
calculated by following formula:
P_D(MAX) = (150℃ - 25℃) / (250℃/W) = 0.5W
PWM
EN
SGM3127
GND
Figure 2. Application Circuit for Keypad
SG Micro Corp
8
www.sg-micro.com