LTC3703EG-5#TR Linear Technology, LTC3703EG-5#TR Datasheet - Page 14

• Manufacturer Part Number: LTC3703EG-5#TR
• Description: IC BUCK/BOOST SYNC ADJ 5A 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Step-Up (Boost)r

Specifications of LTC3703EG-5#TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 55.8 V
• Current - Output: 5A
• Frequency - Switching: 100kHz ~ 600kHz
• Voltage - Input: 9.3 ~ 60 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
appropriate breakdown specification. Since most MOSFETs
in the 30V to 60V range have logic level thresholds
(V
with a 4.5V to 15V gate drive supply (DRV
For maximum efficiency, on-resistance R
capacitance should be minimized. Low R
conduction losses and low input capacitance minimizes
transition losses. MOSFET input capacitance is a combi-
nation of several components but can be taken from the
typical “gate charge” curve included on most data sheets
(Figure 8).
LTC3703-5
The curve is generated by forcing a constant input current
into the gate of a common source, current source loaded
stage and then plotting the gate voltage versus time. The
initial slope is the effect of the gate-to-source and the gate-
to-drain capacitance. The flat portion of the curve is the
result of the Miller multiplication effect of the drain-to-gate
capacitance as the drain drops the voltage across the
current source load. The upper sloping line is due to the
drain-to-gate accumulation capacitance and the gate-to-
source capacitance. The Miller charge (the increase in
coulombs on the horizontal axis from a to b while the curve
is flat) is specified for a given V
adjusted for different V
ratio of the application V
values. A way to estimate the C
change in gate charge from points a and b on a manufac-
turers data sheet and divide by the stated V
specified. C
for determining the transition loss term in the top MOSFET
but is not directly specified on MOSFET data sheets. C
and C
parameters are not included.
When the controller is operating in continuous mode the
duty cycles for the top and bottom MOSFETs are given by:
14
GS(MIN)
V
GS
OS
are specified sometimes but definitions of these
≥ 4.5V), the LTC3703-5 is designed to be used
C
MILLER
MILLER
a
Figure 8. Gate Charge Characteristic
MILLER EFFECT
= (Q
Q
IN
B
is the most important selection criteria
– Q
U
A
)/V
b
DS
DS
U
DS
voltages by multiplying by the
to the curve specified V
DS
MILLER
drain voltage, but can be
W
V
+
GS
–
V
term is to take the
DS(ON)
DS(ON)
CC
+
pin).
–
DS
U
minimizes
V
and input
37035 F08
DS
V
voltage
IN
RSS
DS
The power dissipation for the main and synchronous
MOSFETs at maximum output current are given by:
where δ is the temperature dependency of R
the effective top driver resistance (approximately 2Ω at
V
in drain potential in the particular application. V
data sheet specified typical gate threshold voltage speci-
fied in the power MOSFET data sheet at the specified drain
current. C
gate charge curve from the MOSFET data sheet and the
technique described above.
Both MOSFETs have I
equation includes an additional term for transition losses,
which peak at the highest input voltage. For V
high current efficiency generally improves with larger
MOSFETs, while for V
rapidly increase to the point that the use of a higher
R
efficiency. The synchronous MOSFET losses are greatest
at high input voltage when the top switch duty factor is low
or during a short circuit when the synchronous switch is
on close to 100% of the period.
The term (1 + δ) is generally given for a MOSFET in the
form of a normalized R
typically varies from 0.005/°C to 0.01/°C depending on
the particular MOSFET used.
GS
DS(ON)
P
P
MainSwitchDutyCycle
SynchronousSwitchDutyCycle
MAIN
SYNC
= V
MILLER
device with lower C
=
=
MILLER
V
⎡
⎢
⎢
⎣
V
V
IN
V
V
OUT
IN
CC
IN
2
), V
I
–
V
MAX
–
IN
is the calculated capacitance using the
(
2
IN
V
I
1
MAX
V
OUT
TH IL
is the drain potential and the change
2
(
R losses while the topside N-channel
R
( )
)
DS(ON)
DR
(
IN
2
I
MAX
(
1
)(
+
> 25V, the transition losses
MILLER
=
+
C
V
) (
V
MILLER
δ
2
TH IL
vs temperature curve, and
V
OUT
)
IN
1
R
1
( )
DR ON
+
actually provides higher
δ
(
⎤
⎥
⎥
⎦
=
) •
( )
)
R
f
V
)
DS N
IN
+
( )
–
0
V
IN
DS(ON)
V
IN
OUT
TH(IL)
< 25V, the
, R
is the
DR
37035fa
is