SGM3725 Datasheet, PDF (9/13 Pages) SG Micro Corp – 38V Step-Up LED Driver

SGM3725
APPLICATION INFORMATION
Inductor Selection
A 6.8μH to 22μH inductor is recommended for 10/8/6
series LED applications and 10S4P LED applications. If
high efficiency is a critical requirement, a low DCR
inductor should be selected. The inductor’s saturation
current rating should also exceed the peak input current,
especially for high load current application (like 10S4P).
Capacitor Selection
Small size ceramic capacitors are ideal for SGM3725
application. An input capacitor in the range of 1μF to
22μF and a 0.47µF output capacitor are suggested for
10/8/6 series LED applications. For higher output current
applications like 10S4P, larger value output capacitors
like 2.2µF are recommended to minimize output ripple.
Diode Selection
The current rating of the Schottky diode should exceed
the peak current of the boost converter. The voltage
rating should also exceed the target output voltage.
38V Step-Up LED Driver
LED Maximum Current Setting
LED maximum current setting, I_MAX, is determined by the
feedback resistor (R_SET in Figure 1). The feedback
voltage is internally set at 200mV when the DATA = 1.
The LED current is programmed according to the formula
I_MAX = 200mV/R_SET. For accurate LED current settings,
precision 1% resistors are recommended. The formula
and table for R_SET selection are shown below.
R_SET = 200mV/I_MAX
Table 2. Current Setting Resistor (1% Values)
R_SET (Ω) 1% Values
200
40.2
20.0
13.3
10.0
6.65
2.00
I_MAX Current (mA)
1
5
10
15
20
30
100
Input Power
2.7V~30V
C_IN
22μF
Bias Voltage
2.7V~5.5V
C₁
0.1µF
1kΩ
Brightness control
10μH
L
D1
1
SW
6 _VIN
VOUT ⁵
SGM3725
4 _CTRL
FB ³
GND
2
C_OUT
0.47μF
20mA
10‐Series White LEDs
R_SET
10Ω
Figure 1. Application Circuit for 10 LEDs in Series with 20mA Current (VIN can be tied to input power rail if less than 5.5V)
9
SG Micro Corp
www.sg-micro.com