SGM3131 Datasheet, PDF (10/13 Pages) SG Micro Corp – Driver with Low Dropout Current Source

SGM3131
120mA 4-Channel Charge Pump White LED
Driver with Low Dropout Current Source
APPLICATION INFORMATION
Selecting Capacitors
To get the better performance of SGM3131, the selection
of peripherally appropriate capacitor and value is very
important. These capacitors determine some parameters
such as input/output ripple voltage, power efficiency, and
maximum supply current by charge pump. To reduce the
input and output ripple effectively, the low ESR ceramic
capacitors are recommended. For LED driver
applications, the input voltage ripple is more important
than output ripple. Input ripple is controlled by input
capacitor C_IN, increasing the value of input capacitance
can further reduce the ripple. Practically, the input
voltage ripple depends on the power supply impedance.
The flying capacitors (C_FLY) determine the supply current
capability of the charge pump and to influence the overall
efficiency of system. The lower value will improve
efficiency, but it will limit the LED's current at low input
voltage. For 4 × 30mA load over the entire input range of
2.7V to 5.5V, it is recommended to use a 1μF ceramic
capacitor on the flying capacitors.
Brightness Control
The SGM3131 implements a pulse dimming method to
control the brightness of white LEDs. Users can easily
configure the LED current from 0.5mA to 30mA by a
serial pulse. The dimming of white LEDs' current can be
achieved by applying a pulse signal to the EN pin. There
are totally 16 steps of current could be set by users. The
detail operation of brightness dimming is showed in the
Figure 3.
30μs < t_READY 0.5μs < t_HI
0.5μs < t_LO < 500μs
3ms < t_SHDN
EN
0
1
2
3
45
14
15 0
1
Shutdown
I_LEDx
100% _{15/16 14/16 13/16 12/16 3/16}
2/16
100%
1/16
15/16
Shutdown
Figure 3. Brightness Control by Pulse Dimming
SG Micro Corp
10
www.sg-micro.com