LT3505 LINER [Linear Technology], LT3505 Datasheet - Page 23

• Manufacturer Part Number: LT3505
• Description: Monolithic Dual Tracking 3A Step-Down Switching
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
inductor size by allowing an increase in frequency. A dual
step-down application (Figure 10) steps down the input
voltage (V
voltage to power the second output (V
able to provide enough current for its output plus V
maximum load. Note that the V
minimum input voltage (2V) when the second channel
starts to switch. Delaying channel 2 can be accomplished
by either independent soft-start capacitors or sequencing
with the PG1 output.
For example, assume a maximum input of 24V:
V
IN
Frequency (Hz) ≤
L ≥
= 24V, V
(
V
IN
IN1
– V
OUT1
) to the highest output voltage then uses that
PMEG4005
V
OUT
IN
V
OUT1
= 5V at 1.5A and V
• f
5V
)
• V
V
OUT
IN
47µF
Figure 10. 5V and 1.2V 2-Stage Step-Down Converter with Output Sequencing
V
8.06k
t
OUT
– V
MIN(ON)
SW
+ V
10pF
42.3k
6V TO 24V
OUT1
+ V
D
3.3µH
OUT2
V
D
must be above V
IN
IN2
). V
40.2k
= 1.2V at 1.5A
470pF
4.7µF
OUT1
0.47µF
B360A
must be
0.1µF
SHDN
BST1
SW1
IND1
V
PG1
FB1
V
SS/TRACK1
OUT1
C1
OUT2
V
IN1
IN2
LT3501
GND
SS/TRACK2
Single step-down:
2-Stage Step-Down:
V
V
IN2
BST2
FSET
IND2
Frequency (Hz) ≤
L1=
L2 =
Frequency ≤
Max Frequency = 1.2MHz
L1=
L2 =
SW2
OUT2
PG2
FB2
V
C2
PMEG4005
24 • 392kHz
24 • 1.2MHz
(
(
26.7k
(
(
24 – 1.2
5 – 1.2
24 – 5
24 – 5
24 • 392kHz
5 • 1.2MHz
0.1µF
B360A
100k
0.47µF
)
)
)
32.4k
24 – 0.4 + 0.6
• 5
• 5
470pF
• 1.2
)
• 1.2
1µH
5 + 0.6
190ns
≥ 10µH
≥ 3.3µH
4k
24 – 0.4 + 0.6
≥ 0.76µH
3501 F10
10pF
≥ 2.7µH
1.2 + 0.6
8.06k
190ns
47µF
×2
= 1.2MHz
V
1.2V
OUT2
= 392kHz
LT3501
23
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