SGM3131 Datasheet, PDF (9/13 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
The SGM3131 uses a fractional switched capacitor
charge pump to power up to four white LEDs with a
programmable current for uniform intensity. The part
integrates current sources and automatic mode selection
charge pump. It maintains the high efficiency by utilizing
a 1×/ 1.5× fractional charge pump and current sources.
The small equivalent 1× mode open loop resistance and
ultra-low dropout voltage of current source extend the
operating time of 1× mode and optimize the efficiency in
white LED applications.
Input UVLO
The input operating voltage range of the SGM3131 is
2.7V to 5.5V. An input capacitor at the VIN pin could
reduce ripple voltage. It is recommended to use a
ceramic 1μF or larger capacitance as the input capacitor.
This IC provides an under voltage lockout (UVLO)
function to prevent it from unstable issue when startup.
The UVLO threshold of input rising voltage is set at 2.15V
typically with a hysteresis 50mV.
Soft-Start
The SGM3131 employs a soft start feature to limit the
inrush current. The soft-start circuit prevents the
excessive inrush current and input voltage droop. The
soft-start clamps the input current over a typical period of
200μs.
Mode Decision
The SGM3131 uses a smart mode selection method to
decide the working mode for optimizing the efficiency.
Mode decision circuit senses the output and LED voltage
for up/down selection. The SGM3131 automatically
switches to 1.5× mode whenever the dropout condition is
detected from the current source and returns to 1× mode
whenever the dropout condition releases.
LED Connection
The SGM3131 supports up to 4 white LEDs. The four
LEDs are connected from VOUT to pin 3, 4, 5 and 6
respectively (Figure 1). If the LED is not used, the LED
pin can be connected to GND or be floating. But the pin
LED1 is always required to be connected to LED load.
Figure 2 shows the connection for 3-WLEDs application.
LED Current Adjustment (ISET)
A resistor programs a reference current, which is current
mirrored to set the LED current. The 100% current (16/16)
in each LED is typically 260 times the current through the
resistor at ISET (see Table 1).
R_SET =
V_{ISET ×K}
I_LED
V_ISET — Voltage from ISET pin (0.6V) to GND
I_LED — 100% Current per LED from LEDx pin to GND
K — LEDx to ISET current ratio (typically 260)
The LED current varies linearly from 0mA to I_LED (100%)
by the single wire interface, totally 16-step brightness
dimming.
SET DRIVE
CURRENT
(100%)
30mA
25mA
20mA
10mA
5mA
R_SET COMPUTATION
VALUE(kΩ)
STANDARD
RESISTOR VALUE
(kΩ) (1%)
5.2
5.1
6.24
6.19
7.8
7.68
15.6
15.4
31.2
30.9
Table 1. R_SET Values
SG Micro Corp
9
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