Global Mixed-mode Technology Inc.
Table 2. Recommended Output Capacitors
PART
UMK212BJ104MG
GMK316BJ105KL
GMK316F475ZG
G5114/G5116/G5118
VALUE (µF)
0.1
1
4.7
VOLTAGE
RATING (V)
50
35
35
VENDOR
Tayo Yuden
Tayo Yuden
Tayo Yuden
Setting The LED Current
The Converter regulates the LED current by regulating
the voltage across the current sense resistor (R
S
). The
voltage across the sense resistor is regulated to the
internal reference voltage of V
(FB)
=250mV. The LED
Current can be calculated:
I
LED
=
V
FB
R
S
=
0.25V
R
S
Input Capacitor Selection
For good input voltage filtering the capacitor value can
be increased. Low ESR ceramic capacitors are rec-
ommended. A 4.7µF ceramic input capacitor is suffi-
cient for most applications.
Table 3. Recommended Input Capacitors
PART
LMK212BJ105MG
JMK212BJ475MG
JMK212BJ106MG
VALUE (µF)
1
4.7
10
VOLTATE
RATING (V)
10
6.3
6.3
VENDOR
Tayo Yuden
Tayo Yuden
Tayo Yuden
The current programming method is used when the
brightness of the LEDs is fixed or control by a PWM
signal applied to the
SHDN
pin. When using a PWM
signal on the
SHDN
pin, the LED brightness is only
dependent on the PWM duty cycle, independent of the
PWM frequency or amplitude, which simplifies the sys-
tems.
Layout considerations
In all switching power supplies the layout is an impor-
tant step in the design, especially at high peak currents
and switching frequencies. If the layout is not carefully
done, the regulator might show noise problems and
duty cycle jitter. The input capacitor should be placed
as close as possible to the input pin for good input
voltage filtering. The inductor and diode must be placed
as close as possible to the switch pin to minimize noise
coupling into other circuits. Since the feedback pin and
network is a high impedance circuit, the feedback net-
work should be routed away from the inductor.
Diode Selection
To achieve high efficiency a Schottky diode must be
used. The current rating of the diode must meet the
peak current rating of the converter. Schottky diodes,
with their low forward voltage drop and fast switching
speed, are best match for the G5114/G5116/G5118.
Table 4. Recommended Diodes
PART
MBR0530
REVERSE
VOLTAGE (V)
30
VENDOR
On Semiconductor
Ver: 1.1
Sep 13, 2004
TEL: 886-3-5788833
http://www.gmt.com.tw
7
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
