LM3406HVEVAL National Semiconductor, LM3406HVEVAL Datasheet - Page 20

• Manufacturer Part Number: LM3406HVEVAL
• Description: LM3406/06HV 1.5A Constant Current Buck Regulator for Driving High Power LEDs; Qty per Container: 1/
• Manufacturer: National Semiconductor

www.national.com
C
The bootstrap capacitor C
capacitors with X7R dielectric. A 25V rating is appropriate for
all application circuits. The COMP pin capacitor C
linear regulator filter capacitor C
ceramic capacitors, also with X7R dielectric and a 25V rat-
ings.
EFFICIENCY
To estimate the electrical efficiency of this example the power
dissipation in each current carrying element can be calculated
and summed. Electrical efficiency, η, should not be confused
with the optical efficacy of the circuit, which depends upon the
LEDs themselves. One calculation will be detailed for three
LEDs in series, where V
be repeated for other numbers of LEDs.
Total output power, P
Conduction loss, P
Gate charging and VCC loss, P
regulator:
Switching loss, P
B
, C
P
P
C
P
G
C
S
= (I
= (600 x 10
AND C
= 0.5 x 24 x 1.54 x 40 x 10
F
2
x R
P
P
O
F
S
DSON
P
= I
= 0.5 x V
S
G
, in the internal MOSFET:
F
-6
C
= (I
, in the internal MOSFET:
) x D = (1.54
x V
+ 5 x 10
O
IN-OP
, is calculated as:
O
O
= 11.8V, and these calculations can
B
= 1.54 x 11.8 = 18.2W
IN
should always be a 22 nF ceramic
+ f
x I
5
SW
F
x 9 x 10
G
x (t
2
, in the gate drive and linear
F
x Q
x 0.75) x 0.5 = 890 mW
-9
should always be 100 nF
R
x 5 x 10
+ t
G
) x V
-9
F
) x 24 = 122 mW
FIGURE 15. Schematic for Design Example 2
) x f
IN
5
SW
= 370 mW
C
and the
20
AC rms current loss, P
DCR loss, P
Recirculating diode loss, P
Current Sense Resistor Loss, P
Electrical efficiency, η = P
18.2 / (18.2 + 2.1) = 89%
Temperature Rise in the LM3406 IC is calculated as:
T
Design Example 2
The second example circuit uses the LM3406 to drive a single
white LED at 1.5A ±10% with a ripple current of 20%
typical 12V automotive electrical system. The two-wire dim-
ming function will be employed in order to take advantage of
the legacy 'theater dimming' method which dims and bright-
ens the interior lights of automobiles by chopping the input
voltage with a 200Hz PWM signal. As with the previous ex-
ample, the typical V
current sense voltage of 0.2V the total output voltage will be
4.1V. The LED driver must operate to specifications over an
input range of 9V to 16V as well as operating without suffering
damage at 28V for two minutes (the 'double battery jump-
start' test) and for 300 ms at 40V (the 'load-dump' test). The
LED driver must also be able to operate without suffering
damage at inputs as low as 6V to satisfy the 'cold crank' tests.
A complete bill of materials can be found in
of this datasheet.
LM3406
P
CIN
= I
= (P
P
IN(rms)
L
C
L
= I
, in the inductor
+ P
2
F
2
x ESR = 0.75
G
x DCR = 1.54
+ P
F
of a white LED is 3.9V, and with the
CIN
S
) x θ
, in the input capacitor:
O
D
69°C
JA
= (1 - 0.5) x 1.54 x 0.4 = 300 mW
/ (P
2
= (0.89 + 0.122 + 0.37) x 50 =
2
SNS
0.003 = 2 mW (negligible)
O
x 0.06 = 142 mW
+ Sum of all loss terms) =
= 293 mW
Table 2
30020325
at the end
P-P
in a