Texas Instruments LM3410X Boost LED Driver Evaluation Board LM3410XBSTOVPEV/NOPB LM3410XBSTOVPEV/NOPB 데이터 시트
제품 코드
LM3410XBSTOVPEV/NOPB
V
FB
2
R
SET
P
RSET
=
D
2
x
x
=
R
DSON
¸¸
¹
·
¨¨
©
§
D
'
P
NFET
-
COND
I
LED
Isw-rms = I
IND
D
1 +
'
i
I
IND
1
3
2
x
D
I
IND
|
t
'
i
I
IN
I
SW(t)
SNVS541G – OCTOBER 2007 – REVISED MAY 2013
Figure 23. LM3410 Switch Current
(27)
(small ripple approximation)
P
COND-NFET
= I
IN
2
x R
DSON
x D
(28)
Or
(29)
The value for R
DSON
should be equal to the resistance at the junction temperature you wish to analyze. As an
example, at 125°C and R
DSON
= 250 m
Ω
(See typical graphs for value).
Switching losses are also associated with the internal power switch. They occur during the switch on and off
transition periods, where voltages and currents overlap resulting in power loss.
transition periods, where voltages and currents overlap resulting in power loss.
The simplest means to determine this loss is to empirically measuring the rise and fall times (10% to 90%) of the
switch at the switch node:
switch at the switch node:
P
SWR
= 1/2(V
OUT
x I
IN
x f
SW
x t
RISE
)
(30)
P
SWF
= 1/2(V
OUT
x I
IN
x f
SW
x t
FALL
)
(31)
P
SW
= P
SWR
+ P
SWF
(32)
Table 4. Typical Switch-Node Rise and Fall Times
V
IN
V
OUT
t
RISE
t
FALL
3V
5V
6nS
4nS
5V
12V
6nS
5nS
3V
12V
8nS
7nS
5V
18V
10nS
8nS
Quiescent Power Losses
I
Q
is the quiescent operating current, and is typically around 1.5 mA.
P
Q
= I
Q
x V
IN
(33)
R
SET
Power Loss
(34)
Example Efficiency Calculation:
Operating Conditions:
5 x 3.3V LEDs + 190mV
REF
≊
16.7V
(35)
20
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