LTC3735EUHF Linear Technology, LTC3735EUHF Datasheet - Page 22

IC CTRLR DC/DC 2PH HI EFF 38-QFN

LTC3735EUHF

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

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
-

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Part Number
Manufacturer
Quantity
Price
Part Number:
LTC3735EUHF
Manufacturer:
LT
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Manufacturer:
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APPLICATIO S I FOR ATIO
LTC3735
22
Active Voltage Positioning
Active voltage positioning can be used to minimize peak-
to-peak output voltage excursion under worst-case tran-
sient loading conditions. The open-loop DC gain of the
control loop is reduced depending upon the maximum
load step specifications. Active voltage positioning can
easily be added to the LTC3735. Figure 9 shows the
equivalent circuit for implementing AVP. The load line
slope is estimated to be:
where R
number of phases, (m = 2 for LTC3735) R
defined in Figure 9. g
error amplifier, it is about 4.5mmho for LTC3735. Rewrit-
ing Equation 9 we can estimate the AVP resistor to be:
AVP
R
if g
AVP
m
SENSE
R2
– . •
R
Figure 9. Simplified Schematic Diagram
for AVP Design in LTC3735
R1
35 5
35 5
3 10
V
OUT+
>
. •
R3
is the current sense resistor, m is the
m AVP
V
V
VID
R R
• |
OA
OA
R
U
3
SENSE
+
m
V
0 6
m
OUT
.
is the transconductance gain for the
0.6V
SENSE
V
|
U
FB
R
R
+
+
AVP
R
3
AVP
,
W
OAOUT
3
and R
I
TH
3735 F09
U
AVP
(10)
(9)
are
We also adopt the current sense resistors as part of
voltage positioning slopes. So the total load line slope is
estimated to be:
Rewriting this equation, we can estimate the R
be:
Typically the calculation results based on these equations
have ±10% tolerance. So the resistor values need to be fine
tuned.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can be
expressed as:
where L1, L2, etc. are the individual losses as a percentage
of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3735 circuits: 1) I
MOSFET transition losses, 3) PV
C
1) I
fuse (if used), MOSFET, inductor, and current sense
resistor. In continuous mode the average output current
flows through L and R
IN
%Efficiency = 100% – (L1 + L2 + L3 + ...)
R
AVP
2
loss.
R losses are predicted from the DC resistances of the
AVP
– . •
m AVP
if g
R
35 5
35 5
• |
SENSE
m
. •
R
R
R
3
SENSE
|
3
m
>>
SENSE
1
V
0 6
OUT
.
, but is “chopped” between the
R
V
R
AVP
3
CC
2
R losses, 2) Topside
supply current and 4)
R
SENSE
m
,
AVP
value to
(11)
(12)
3735f

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