LT1054CSW#TRMPBF Linear Technology, LT1054CSW#TRMPBF Datasheet - Page 9

• Manufacturer Part Number: LT1054CSW#TRMPBF
• Manufacturer: Linear Technology
• Type: Inverting/Step Upr

Specifications of LT1054CSW#TRMPBF

• Operating Supply Voltage (min): 3.5V
• Operating Supply Voltage (max): 15V
• Operating Temp Range: 0C to 100C
• Operating Temperature Classification: Commercial
• Package Type: SOIC W
• Pin Count: 16
• Mounting: Surface Mount
• Output Voltage: AdjV
• Output Current: 100mA
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS
where dV = peak-to-peak ripple and f = oscillator frequency.
For output capacitors with significant ESR a second term
must be added to account for the voltage step at the switch
transitions. This step is approximately equal to:
Power Dissipation
The power dissipation of any LT1054 circuit must be
limited such that the junction temperature of the device
does not exceed the maximum junction temperature rat-
ings. The total power dissipation must be calculated from
two components, the power loss due to voltage drops in the
switches and the power loss due to drive current losses.
The total power dissipated by the LT1054 can be calculated
from:
where both V
3) of the LT1054. For LT1054 regulator circuits, the power
dissipation will be equivalent to that of a linear regulator.
Due to the limited power handling capability of the LT1054
packages, the user will have to limit output current require-
ments or take steps to dissipate some power external to the
LT1054 for large input/output differentials. This can be
accomplished by placing a resistor in series with C
shown in Figure 6. A portion of the input voltage will then
be dropped across this resistor without affecting the output
regulation. Because switch current is approximately 2.2
times the output current and the resistor will cause a
voltage drop when C
the resistor should be chosen as:
(2I
P (V
OUT
)(ESR of C
IN
C
IN
–
+
IN
|
V
and V
RX
OUT
|
U
FB/SHDN
CAP
GND
CAP
OUT
)(I
OUT
IN
LT1054
OUT
+
–
)
is both charging and discharging,
are referred to the ground pin (Pin
INFORMATION
V
V
V
Figure 6
) + (V
OSC
U
OUT
REF
OUT
V
+
V
IN
IN
+
)(I
C
OUT
W
OUT
R1
R2
C1
LT1054 • F06
)(0.2)
U
IN
as
where
and I
1.3 will allow some operating margin for the LT1054.
For example: assume a 12V to – 5V converter at 100mA
output current. First calculate the power dissipation with-
out an external resistor:
At
would cause a junction temperature rise of 122 C so that
the device would exceed the maximum junction tempera-
ture at an ambient temperature of 25 C. Now calculate the
power dissipation with an external resistor (R
how much voltage can be dropped across R
mum voltage loss of the LT1054 in the standard regulator
configuration at 100mA output current is 1.6V, so
This resistor will reduce the power dissipated by the
LT1054 by (4.9V)(100mA) = 490mW. The total power
dissipated by the LT1054 would then be (940mW –
490mW) = 450mW. The junction temperature rise would
now be only 58 C. Although commercial devices are
guaranteed to be functional up to a junction temperature
of 125 C, the specifications are only guaranteed up to a
junction temperature of 100 C, so ideally you should limit
the junction temperature to 100 C. For the above example
this would mean limiting the ambient temperature to 42 C.
Other steps can be taken to allow higher ambient tempera-
tures. The thermal resistance numbers for the LT1054
packages represent worst case numbers with no heat
sinking and still air. Small clip-on type heat sinks can be
used to lower the thermal resistance of the LT1054 pack-
age. In some systems there may be some available airflow
which will help to lower the thermal resistance. Wide PC
board traces from the LT1054 leads can also help to
remove heat from the device. This is especially true for
plastic packages.
R
V
P = (12V –
P = 700mW + 240mW = 940mW
V
R
X
X
X
X
JA
OUT
= 12V – [(1.6V)(1.3) +
= V
= 4.9V/(4.4)(100mA) = 11
of 130 C/W for a commercial plastic device this
V
= maximum required output current. The factor of
X
IN
/(4.4 I
– [(LT1054 Voltage Loss)(1.3) +
|
– 5V
OUT
|
)
)(100mA) + (12V)(100mA)(0.2)
LT1054/LT1054L
|
– 5V
|
] = 4.9V and
X
|
X
V
. The maxi-
). First find
OUT
|
]
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