SC2544TSTRT Semtech, SC2544TSTRT Datasheet - Page 14

• Manufacturer Part Number: SC2544TSTRT
• Description: IC CTRL/REG SYNC BUCK 24-TSSOP
• Manufacturer: Semtech
• Type: Step-Down (Buck)r

Specifications of SC2544TSTRT

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: Adj to 0.75V
• Frequency - Switching: 100kHz ~ 300kHz
• Voltage - Input: 4.5 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Other names: SC2544TSTR

T T T T T op Switc
The RMS value of the top switch current is calculated
as
The conduction losses are then
R
voltage. Curves showing R
in manufacturers’ data sheet. From the Si4860
datasheet, R
than 10V. However R
junction temperature increases from 25
The switching losses can be estimated using the simple
formula
where t
switching process. Different manufactures have
different definitions and test conditions for t
t
switching characteristics under clamped inductive
mode in Figure 9.
POWER MANAGEMENT
Applications Information (Cont.)
f
op Switc
op Switc
op Switc
op Switch h h h h
ds(on)
. To clarify these, we sketch the typical MOSFET
2005 Semtech Corp.
V o lts
V o lts
varies with temperature and gate-source
Figure 9. MOSFET switching characteristics
r
t0
t0
V gs th
V gs th
is the rise time and t
Q gs1 Q gs2
Q gs1 Q gs2
V d s
V d s
ds(on)
t1
t1
I
P
t2
t2
Q
is less than 8m
P
, 1
tc
rms
ts
= I
Q gd
Q gd
Q1,rms
I
ds(on)
2
1
o
t (
D
r
2
ds(on)
1 (
R
increases by 50% as the
M iller plateau
M iller plateau
t3
t3
ds(on)
t
Ids
Ids
f
12
variations can be found
)(
f
2
. )
is the fall time of the
1
.
when V
2
V gs
V gs
I )
o
V
in
o
C to 110
. f
gs
s
G ate charge
G ate charge
is greater
r
and
o
C.
14
In Figure 9, Q
the gate-to-source voltage V
V
Q
switch current to reach its full-scale value I
is the charge needed to charge gate-to-drain (Miller)
capacitance when V
Switching losses occur during the time interval [t
t
where R
rail to the gate of the MOSFET. It includes the gate
driver internal impedance R
and the gate resistance R
V
Similarly an approximate expression for t
Only a portion of the total losses P
dissipated in the MOSFET package. Here Q
total gate charge specified in the datasheet. The
power dissipated within the MOSFET package is
The total power loss of the top switch is then
If the input supply of the power converter varies
over a wide range, then it will be necessary to
weigh the relative importance of conduction and
switching losses. This is because conduction losses
are inversely proportional to the input voltage.
Switching loss however increases with the input
voltage. The total power loss of MOSFET should be
calculated and compared for high-line and low-line
cases. The worst case is then used for thermal
design.
3
gsp
g s _ t h
gs2
]. Defining t
is the Miller plateau voltage shown in Figure 9.
is the additional gate charge required for the
.
gt
is the total resistance from the driver supply
r
gs1
= t
is the gate charge needed to bring
t
3
r
-t
R
P
t
1
ds
f
gt
tg
(
P
and t
Q
= R
is falling.
t
(
= P
gs
V
Q
R
R
2
cc
gi
gs
gt
g
g
+R
tc
r
2
gs
within the MOSFET :
Q
+P
Q
gi
can be approximated as
V
V
, external resistance R
g
ge
to the threshold voltage
gsp
gd
V
Q
gsp
ts
+R
cc
R )
+P
gd
. f
R )
s
gt
g
tg
.
.
.
gt
.
www.semtech.com
SC2544
g
= Q
f
is
ds
,
.
g
g
and Q
V
is the
cc
f
s
is
gd
1
ge
,