LM34919_14 Datasheet, PDF (13/21 Pages) Texas Instruments – Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator

LM34919
www.ti.com
SNOSAY2D – MAY 2007 – REVISED JUNE 2008
t₂ x 10.5 PA
C6 = _2.5V = 0.021 PF
(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 7, and its performance is shown in Figure 8 and Figure 9. Current limit
measured approximately 650 mA at 8V, and 740 mA at 40V.
8V - 40V
Input
C1
2.2 PF
C5
0.1 PF
R_ON
43.2 k:
SHUTDOWN
C6
0.022 PF
VCC
VIN
LM34919
BST
RON/SD
SS
RTN
SW
ISEN
FB
SGND
C3
0.1 PF
C4
L1
0.022 PF ^{15 PH}
D1
R1
2.49 k:
R2
2.49 k:
V_OUT
5V
R3
0.39:
C2
22 PF
Figure 7. Example Circuit
Figure 8. Efficiency vs. Load Current and V_IN
(Circuit of Figure 7)
Figure 9. Frequency vs. V_IN (Circuit of Figure 7)
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.
Copyright © 2007–2008, Texas Instruments Incorporated
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