lt3740 Linear Technology Corporation, lt3740 Datasheet - Page 15

• Manufacturer Part Number: lt3740
• Description: Wide Operating Range, Valley Mode, No Rsense Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
At no load, the maximum reverse current voltage is:
Which is adequately lower than the 35mV reverse current
comparator threshold.
C
85°C. The output capacitors are chosen for a low ESR of
0.005Ω to minimize output voltage changes due to
inductor ripple current and load steps. The ripple voltage
will be only:
IN
ΔV
R
is chosen for an RMS current rating of about 5A at
S
OUT(RIPPLE)
•
Δ
I
L MAX
(
2
= ΔI
)
U
=
L
12
• (ESR) = (3.47A)(0.005Ω) = 17mV
m
U
Ω
18pF
•
3 65
.
2
100k
100k
W
22μH
100k
L2
100pF
1μF
A
=
Figure 4. Design Example: 2.5V/10A Output
SWB
V
RANGE
SHDN
XREF
PGOOD
V
22
IN
C
mV
U
LT3740
GND
TGATE
BGATE
BGDP
PGND
BIAS
SN
SN
SW
FB
+
–
1μF
C
B
However, a 0A to 10A load step will cause an output
change of up to:
An optional 100μF ceramic output capacitor is included to
minimize the effect of ESL in the output ripple.
For the step-up converter, at V
current is about 27mA. Choose a 22μH inductor and a
1μF output capacitor.
The complete circuit is shown in Figure 4.
ΔV
M1
Si4840
M2
Si4840
OUT(STEP)
R
12mΩ
S
D1
6CWQ03FN
C
100μF
35V
V
7V to 20V
= ΔI
IN
L1 2.0μH
IN
LOAD
21k
10k
• (ESR) = (10A)(0.005Ω)= 50mV
3740 F04
680μF
4V × 2
IN
= 7V, step-up inductor
100μF
6.3V
V
10A
OUT
2.5V
LT3740
15
3740fa