LTC3734EUH Linear Technology, LTC3734EUH Datasheet - Page 20

• Manufacturer Part Number: LTC3734EUH
• Description: IC CTRLR DC/DC 1PH HI EFF 32QFN
• Manufacturer: Linear Technology

Specifications of LTC3734EUH

• Applications: Controller, Intel Mobile CPU
• Voltage - Input: 4 ~ 30 V
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 1.71 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-QFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC3734
where
Rewriting equation (9) we can estimate the AVP resistor to
be:
We also adopt the current sense resistors as part of
voltage positioning slopes. So the total load line slope is
estimated to be:
20
AVP is the slope, in mV/A
R
m is the number of phases, m = 1 for LTC3734
R3 and R
g
it is about 4.5mmho for LTC3734.
R
AVP
if g
m
SENSE
AVP
is the transconductance gain for the error amplifier,
m
≅
•
≅
R
– . •
is the current sense resistor
R2
35 5
3
35 5
AVP
R1
Figure 6. Simplified Schematic
Diagram for AVP Design in LTC3734
V
>>
OUT+
. •
m AVP
R3
are defined in Figure 6
V
0 6
R
• |
V
V
R
VID
OUT
.
OA
OA
3
U
SENSE
+
–
V
•
m
R
SENSE
0.6V
|
U
•
FB
R
R
AVP
–
–
+
+
3
R
AVP
–
W
R
SENSE
m
OAOUT
,
I
TH
U
3735 F09
(10)
(11)
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 LTC3734 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
topside MOSFET and the synchronous MOSFET. If the two
MOSFETs have approximately the same R
resistance of one MOSFET can simply be summed with the
resistances of L, R
example, if each R
= 5mΩ, then the total resistance is 25mΩ. This results in
losses ranging from 2% to 8% as the output current
increases from 3A to 15A per output stage for a 5V output,
or a 3% to 12% loss per output stage for a 3.3V output.
IN
%Efficiency = 100% – (L1 + L2 + L3 + ...)
R
2
loss.
R losses are predicted from the DC resistances of the
AVP
≅
m AVP
R
35 5
• |
SENSE
. •
DS(ON)
SENSE
R
|
3
SENSE
–
1
and ESR to obtain I
= 10mΩ, R
, but is “chopped” between the
CC
2
R losses, 2) Topside
L
supply current and 4)
= 10mΩ, and R
DS(ON)
2
R losses. For
AVP
, then the
value to
SENSE
(12)
3734f