LM3492MH/NOPB National Semiconductor, LM3492MH/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM3492MH/NOPB
• Description: IC LED DVR DIM 2CH 20-TSSOP
• Manufacturer: National Semiconductor

Specifications of LM3492MH/NOPB

• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: High Brightness LED (HBLED)
• Mounting Type: Surface Mount
• Topology: Step-Up (Boost)
• Number Of Outputs: 2
• Frequency: 200kHz ~ 1MHz
• Voltage - Supply: 4.5 V ~ 65 V
• Package / Case: 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
• Operating Temperature: -40°C ~ 125°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

As a result, I
selected for L
D
tors. The first factor is the reverse voltage, which equals to
V
diode current at the steady state, which equals to the peak
inductor current as shown in (10). In this example, a 100V 3A
schottky diode is selected.
C
output capacitor C
age ripples. Experimentation is usually necessary to deter-
mine their value. The rated DC voltage of capacitors used
should be higher than the maximum DC voltage applied. Ow-
ing to the concern of product lifetime, ceramic capacitors are
recommended. But ceramic capacitors with high rated DC
voltage and high capacitance are rare in general. Multiple ca-
pacitors connecting in parallel can be used for C
C
for C
C
and stabilizes the LDO regulator. It also prevents false trig-
gering of the VCC UVLO. C
good quality and low ESR ceramic capacitor.
C
sensitivity of the DHC but also determines the soft-start time
t
t
SS
SS
OUT
1
IN
OUT
VCC
CDHC
: The selection of the boost diode D
, i.e. the time for the output voltage to rise until power good.
is determined from the following equation:
and C
IN
. In this example, two 10 µF ceramic capacitor are used
: The capacitor on the VCC pin provides noise filtering
for a boost converter. The second factor is the peak
: The capacitor at the CDHC pin not only affects the
, and two 2.2 µF ceramic capacitor are used for C
OUT
L1(PEAK)
1
: The function of the input capacitor C
, and its saturation current is larger than 1.98A.
OUT
is 1.98A. A standard value of 47 µH is
is to reduce the input and output volt-
VCC
is recommended to be a 1 µF
1
depends on two fac-
IN
and the
IN
OUT
and
.
13
In this example, C
quality and low ESR ceramic capacitor.
R
frequency f
I
lected to be 499 kΩ. From Figure 4, if I
is selected to be 6.19 kΩ.
R
R
pins to act as a pull-up function.
PC Board Layout
The layout of the printed circuit board is critical in order to
optimize the performance of the LM3492 application circuit.
In general, external components should be placed as close to
the LM3492 and each other as possible in order to make cop-
per traces short and direct. In particular, components of the
boost converter C
closed. Also, the output feedback capacitor C
closed to the output capacitor C
necting the GND, PGND, and LGND pins and the exposed
pad of the LM3492 and the ground connection of the C
C
Good heat dissipation helps optimize the performance of the
LM3492. The ground plane should be used to connect the
exposed pad of the LM3492, which is internally connected to
the LM3492 die substrate. The area of the ground plane
should be extended as much as possible on the same copper
layer around the LM3492. Using numerous vias beneath the
exposed pad to dissipate heat of the LM3492 to another cop-
per layer is also a good practice.
LED
RT
COMM
COMM
OUT
and R
respectively. From Figure 1, if f
should be placed on the same copper layer.
: Since the COMM pin is open drain, a resistor
of 52.3 kΩ is used to connect the VCC and COMM
IREF
SW
: The resistors R
of the boost converter and the LED current
CDHC
IN
, L
1
, D
is recommended to be a 0.47 µF good
1
, C
OUT
RT
OUT
, and the LM3492 should be
and R
SW
. The ground plane con-
is 300 kHz, R
IREF
LED
is 200 mA, R
set the switching
FB
www.national.com
should be
30116110
RT
IN
is se-
IREF
and