Datasheet

LM2735
SNVS485F –JUNE 2007–REVISED APRIL 2013 www.ti.com
Table 1. 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 7nS 5nS
5V 18V 7nS 5nS
Quiescent Power Losses
I
Q
is the quiescent operating current, and is typically around 4mA.
P
Q
= I
Q
x V
IN
(34)
Example Efficiency Calculation:
Table 2. Operating Conditions
V
IN
5V
V
OUT
12V
I
OUT
500mA
V
D
0.4V
F
SW
1.60MHz
I
Q
4mA
T
RISE
6nS
T
FALL
5nS
R
DSon
250mΩ
R
DCR
50mΩ
D 0.64
I
IN
1.4A
ΣP
COND
+ P
SW
+ P
DIODE
+ P
IND
+ P
Q
= P
LOSS
(35)
Quiescent Power Losses
P
Q
= I
Q
x V
IN
= 20 mW (36)
Switching Power Losses
P
SWR
= 1/2(V
OUT
x I
IN
x F
SW
x T
RISE
) ≊ 6 ns ≊ 80 mW (37)
P
SWF
= 1/2(V
OUT
x I
IN
x F
SW
x T
FALL
) ≊ 5 ns ≊ 70 mW (38)
P
SW
= P
SWR
+ P
SWF
= 150 mW (39)
Internal NFET Power Losses
R
DSON
= 250 mΩ (40)
P
CONDUCTION
= I
IN
2
x D x R
DSON
x 305 mW (41)
Diode Losses
V
D
= 0.45V (42)
P
DIODE
= V
D
x I
IN
(1-D) = 236 mW (43)
Inductor Power Losses
R
DCR
= 75 mΩ (44)
P
IND
= I
IN
2
x R
DCR
= 145 mW (45)
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