LTC3448EMS8E Linear Technology, LTC3448EMS8E Datasheet - Page 11

• Manufacturer Part Number: LTC3448EMS8E
• Description: IC CONV DC/DC SYNC STEPDWN 8MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3448EMS8E

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5.2 V
• Current - Output: 600mA
• Frequency - Switching: 1.5MHz ~ 2.25MHz
• Voltage - Input: 2.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP Exposed Pad, 8-HMSOP, 8-eMSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
Efficiency Considerations
The 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. 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, two main sources usually account for most of the
losses in LTC3448 circuits: V
losses. When in switching mode, V
worst, a sudden inrush of current through the long wires
can potentially cause a voltage spike at V
to damage the part.
When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage charac-
teristics of all the ceramics for a given value and size.
Output Voltage Programming
The output voltage is set by tying V
according to the following formula:
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 5.
Efficiency = 100% – (L1 + L2 + L3 + ...)
V
OUT
Figure 5. Setting the LTC3448 Output Voltage
=
0 6 1
.
V
⎛
⎜
⎝
LTC3448
+
U
R
R
GND
2
V
1
FB
⎞
⎟
⎠
U
IN
quiescent current and I
0.6V ≤ V
W
FB
IN
OUT
to a resistive divider
R2
R1
quiescent current
3448 F05
≤ 5.5V
IN
, large enough
U
(2)
2
R
loss dominates the efficiency loss at low load currents,
whereas the I
medium to high load currents. At very low load currents
with the part operating in LDO mode, efficiency can be
dominated by I
strong function of (V
the efficiency curve at very low load currents can be
misleading since the actual power lost is of little conse-
quence as illustrated in Figure 6.
1. The V
2. I
the DC bias current as given in the Electrical Character-
istics and the internal main switch and synchronous
switch gate charge currents. The gate charge current
results from switching the gate capacitance of the
internal power MOSFET switches. Each time the gate is
switched from high to low to high again, a packet of
charge, dQ, moves from V
dQ/dt is the current out of V
the DC bias current and proportional to frequency. Both
the DC bias and gate charge losses are proportional to
V
higher supply voltages.
internal switches, R
continuous mode, the average output current flowing
through inductor L is “chopped” between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
2
IN
R losses are calculated from the resistances of the
and thus their effects will be more pronounced at
0.0001
IN
0.001
0.01
0.1
0.0001
quiescent current is due to two components:
1
Figure 6. Power Loss vs Load Current
V
FREQ = 0V
LDOCNTRL = V
2
IN
R loss dominates the efficiency loss at
2
R losses in the pass transistor and is a
= 3.6V
0.001
IN
LOAD CURRENT (A)
– V
SW
OUT(AUTO)
OUT
, and external inductor R
0.01
IN
). In a typical efficiency plot,
IN
that is typically larger than
to ground. The resulting
0.1
1.2V
1.5V
1.8V
3448 F06
LTC3448
1
11
L
. In
3448f