LTC3735EUHF Linear Technology, LTC3735EUHF Datasheet - Page 25

• Manufacturer Part Number: LTC3735EUHF
• Description: IC CTRLR DC/DC 2PH HI EFF 38-QFN
• Manufacturer: Linear Technology

Specifications of LTC3735EUHF

• Applications: Controller, Intel Mobile CPU
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 1.71 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

Tie the FREQSET pin to 1.2V, resistively divided down
from PV
The minimum on-time also occurs at maximum input
voltage:
which is larger than 150ns, the typical minimum on time
of the LTC3735.
R
vative maximum sense voltage threshold of 40mV and
taking into account of the peak current:
The power loss dissipated by the top MOSFET can be
calculated with equations 3 and 7. Using a Fairchild
FDS7760 as an example: R
V
voltage with T
temperature:
Equation 4 gives the worst-case power loss dissipated by
the bottom MOSFET (assuming FDS7760 and T
again):
APPLICATIO S I FOR ATIO
GS
SENSE1
P
R
P
t
TOP
ON MIN
, C
BOT
SENSE
(
RSS
=
CC
=
=
and R
0 008
2
1 5
)
21
(
2 95
21
=
.
Ω
to have 350kHz operation for each phase.
= 307pF, V
.
1 0 005 85
.
=
+
V
V
40
V
•
J
SENSE2
V
21
21
V
(estimated) = 85°C at an elevated ambient
⎛
⎜
⎝
– .
W
IN
•
Ω +
OUT
mV
.
5
V
A
⎛
⎜
⎝
1 5
V
•
35
f
U
1
–
2
V
=
21
=
can be calculated by using a conser-
•
A
1
0 002
(
TH(MIN)
•
V
⎞
⎟
⎠
V
21
.
⎛
⎜
⎝
2
2
+
35
V
U
DS(ON)
•
°
•
2
2
1
C
(
17 5
1 5
•
1
1 0 005 85
V
A
Ω
.
–
350
+
⎞
⎟ =
⎠
⎞
⎟
⎠
.
= 1V. At maximum input
25
V
2
A
= 8mΩ, Q
.
kHz
•
°
1 26
•
C
.
W
350
)
)
=
•
• .
W
(
0 008
204
kHz
G
°
ns
= 55nC at 5V
C
•
307
Ω
–
U
25
J
= 85°C
pF
°
C
•
)
)
•
Therefore it is necessary to have two FDS7760s in parallel
to split the power loss.
A short-circuit to ground will result in a folded back current
of about:
The worst-case power dissipation by the bottom MOSFET
under short-circuit conditions is:
which is less than normal, full load conditions.
The nominal duty cycle of this application is equation 1:
Using Figure 4, the RMS input ripple current will be:
An input capacitor(s) with a 8A RMS current rating is
required.
The output capacitor ripple current is calculated by using
the inductor ripple current and multiplying by the factor
obtained from Figure 3. The output ripple will be highest at
the maximum input voltage since the duty cycle is less
than 50%. The maximum output current ripple is:
Assuming the ESR of output capacitor(s) is 5mΩ, the
output ripple voltage is:
Δ
I
I
P
DC
Δ
INRMS
SC
V
BOT
I
OUT
OUT MAX
=
=
=
=
1 5
0 002
(
12
=
≈
25
2 48
= 35A • 0.22 = 7.7A
.
.
(
350
1 0 005 85
.
5 5
28 4
V
V
mV
+
.
)
.
1
=
W
kHz
A
Ω
=
350
.
mV
P-P
12 5
350
+
1
kHz
. %
P-P
–
⎛
⎜
⎝
2
1
5
•
200
kHz
•
m
(
1 5
⎛
⎜
⎝
Ω +
.
200
ns
• .
°
V
C
0 6
0 6
•
ns
16 350
.
–
(
μ
16
25
μ
•
•
H
H
21
A
°
C
• .
)
V
0 77 5 5
2
)
)
⎞
⎟ =
⎠
kHz
•
• .
0 008
LTC3735
16
=
1
•
(
A
4 270
.
Ω
•
A
P-P
25
μ
F
3735f
)
⎞
⎟
⎠