SGM3736 Datasheet, PDF (9/12 Pages) SG Micro Corp – PWM Dimming, 38V Step-Up LED Driver

SGM3736
PWM Dimming, 38V Step-Up LED Driver
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 SGM3736
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.
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 PWM
dimming duty cycle = 100%. 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 1. 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
Layout Considerations
PCB layout is very important for high frequency switching
regulators in order to keep the loop stable and minimize
noise. The input capacitor should be very close to the IC
to get the best decoupling. The path of the inductor and
output capacitor should be kept as short as possible to
minimize noise and ringing.
Input Power
2.7V~30V
C_IN
22μF
Bias Voltage
2.7V~5.5V
C₁
0.1µF
PWM
Dimming
10μH
L
D1
8
SW
2 _VIN
VOUT ⁷
SGM3736
3 _EN/PWM
FB ⁶
1kΩ
GND
4
PGND
1
RSET
5
R_SET
10Ω
C_OUT
0.47µF
20mA
10-Series White LEDs
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)
SG Micro Corp
9
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