LM34919C-Q1 Datasheet, PDF (19/29 Pages) Texas Instruments – LM34919C-Q1 Ultra Small 50V, 600 mA Constant On-Time Buck Switching Regulator

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LM34919C-Q1
SNVS831A – SEPTEMBER 2013 – REVISED DECEMBER 2013
95
90
4.5V
85 _9V
80
75
70
12V
18V
65
24V
60
55
0.2
0.3
0.4
0.5
0.6
LOAD CURRENT (A)
Figure 10. Efficiency (1.5 MHz, V_OUT = 3.3 V)
3
2.5
2
1.5
1
Ron=61.9k
0.5
4
8
12 16 20 24 28
INPUT VOLTAGE (V)
Figure 11. Frequency vs. V_IN (V_OUT = 3.3 V)
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.
a) Reduced ripple configuration: In Figure 12, Cff is added across R1 to AC-couple the ripple at V_OUT directly
to the FB pin. This allows the ripple at V_OUT to be reduced to a minimum of 25 mVp-p by reducing R3, since the
ripple at V_OUT is not attenuated by the feedback resistors. The minimum value for Cff is determined from:
Cff = ^{tON (max) x 3}
(R1//R2)
(16)
where t_ON(max) is the maximum on-time, which occurs at V_IN(min). The next larger standard value capacitor should
be used for Cff. R1 and R2 should each be towards the upper end of the 2 kΩ to 10 kΩ range.
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