PWM Dimming, 38V Step-Up LED Driver

9

SGM3736

SG Micro Corp

www.sg-micro.com

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

voltage is internally set at 200mV when the PWM

dimming duty cycle = 100%. The LED current is

For accurate LED current settings, precision 1% resistors

selection are shown below.

Table 1. Current Setting Resistor (1% Values)

200

1

40.2

5

20.0

10

13.3

15

10.0

20

6.65

30

2.00

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.

VIN

EN/PWM

PGND

FB

VOUT

D1

0.47µ

F

Input Power

2.7V~30V

22

μF

SGM3736

L

SW

20mA

10-Series White LEDs

8

2

1

7

3

6

Bias Voltage

2.7V~5.5V

0.1µ

F

10

μH

PWM

Dimming

1k

Ω

10

Ω

RSET

5

GND

4

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)