Datasheet

FB
SW
LM34919
BST
VCC
D1
ISEN
RON/SD
VIN
8V - 40V
Input
SS
RTN
SGND
V
OUT
5V
C1
2.2 PF
SHUTDOWN
C6
0.022 PF
C5
0.1 PF
R
ON
43.2 k:
C3
0.1 PF
C4
0.022 PF
L1
15 PH
R3
0.39:
C2
22 PF
R1
2.49 k:
R2
2.49 k:
C6 =
t
2
x 10.5 PA
2.5V
= 0.021 PF
LM34919
www.ti.com SNOSAY2E –MAY 2007–REVISED FEBRUARY 2013
(15)
D1: A Schottky diode is recommended. Ultra-fast recovery diodes are not recommended as the high speed
transitions at the SW pin may inadvertently affect the IC's operation through external or internal EMI. The diode
should be rated for the maximum input voltage, the maximum load current, and the peak current which occurs
when the current limit and maximum ripple current are reached simultaneously. The diode's average power
dissipation is calculated from:
P
D1
= V
F
x I
OUT
x (1-D) (16)
where V
F
is the diode's forward voltage drop, and D is the on-time duty cycle.
FINAL CIRCUIT
The final circuit is shown in Figure 15, and its performance is shown in Figure 16 and Figure 17. Current limit
measured approximately 650 mA at 8V, and 740 mA at 40V.
Figure 15. Example Circuit
Figure 16. Efficiency vs. Load Current and V
IN
Figure 17. Frequency vs. V
IN
(Circuit of Figure 15)
(Circuit of Figure 15)
LOW OUTPUT RIPPLE CONFIGURATIONS
For applications where lower ripple at V
OUT
is required, the following options can be used to reduce or nearly
eliminate the ripple.
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