LT1054CSW Linear Technology, LT1054CSW Datasheet - Page 8

• Manufacturer Part Number: LT1054CSW
• Description: IC VOLT CONV SW-CAP W/REG 16SOIC
• Manufacturer: Linear Technology
• Type: Switched Capacitor (Charge Pump), Doubler, Invertingr

Specifications of LT1054CSW

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 100mA
• Frequency - Switching: 25kHz
• Voltage - Input: 3.5 ~ 15 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LT1054/LT1054L
APPLICATIONS INFORMATION
be 20k or greater because the reference output current
is limited to ≈100µA. R2 should be chosen to be in the
range of 100k to 300k. For optimum results the ratio of
C
good load regulation at light load currents, should be
0.002µF for all output voltages.
A new die layout was required to fit into the physical
dimensions of the S8 package. Although the new die
of the LT1054CS8 will meet all the specifications of the
existing LT1054 data sheet, subtle differences in the
layout of the new die require consideration in some ap-
plication circuits. In regulating mode circuits using the
1054CS8 the nominal values of the capacitors, C
C
at elevated junction temperatures. This is different from
the earlier part. Mismatches within normal production
tolerances for the capacitors are acceptable. Making the
nominal capacitor values equal will ensure proper opera-
tion at elevated junction temperatures at the cost of a
small degradation in the transient response of regulator
circuits. For unregulated circuits the values of C
C
tions assistance in unusual applications circuits, please
consult the factory.
It can be seen from the circuit block diagram that the
maximum regulated output voltage is limited by the supply
voltage. For the basic configuration,
8
R2
R1
R2 = 20k
WHERE V
FOR EXAMPLE: TO GET V
PIN OF THE LT1054, CHOOSE R1 = 20k, THEN
*CHOOSE THE CLOSEST 1% VALUE
IN
OUT
OUT
=
/C
)
RESTART SHUTDOWN
V
, must be approximately equal for proper operation
OUT
are normally equal for all packages. For S8 applica-
REF
2
R3
R4
)
|
REF
V
2.5V
OUT
– 40mV
2
= 2.5V NOMINAL
|
is recommended to be 1/10. C1, required for
–5V
|
– 40mV
|
+ 1
)
+ 1
≈
OUT
)
)
|
TANTALUM
1.21V
V
= –5V REFERRED TO THE GROUND
= 102.6k*
OUT
|
10µF
+ 1
C
Figure 5
IN
)
+
FB/SHDN
CAP
GND
CAP
|
LT1054
V
+
–
OUT
V
V
V
OSC
OUT
REF
OUT
V
|
+
referred to the
V
IN
+
C
100µF
TANTALUM
+
OUT
2.2µF
R1
R2
IN
C1
IN
LT1054 • F05
and
and
ground pin of the LT1054 must be less than the total of the
supply voltage minus the voltage loss due to the switches.
The voltage loss versus output current due to the switches
can be found in Typical Performance Characteristics. Other
configurations such as the negative doubler can provide
higher output voltages at reduced output currents (see
Typical Applications).
Capacitor Selection
For unregulated circuits the nominal values of C
should be equal. For regulated circuits see the section on
Regulation. While the exact values of C
noncritical, good quality, low ESR capacitors such as solid
tantalum are necessary to minimize voltage losses at high
currents. For C
be multiplied by four due to the fact that switch currents
are approximately two times higher than output current and
losses will occur on both the charge and discharge cycle.
This means that using a capacitor with 1Ω of ESR for C
will have the same effect as increasing the output imped-
ance of the LT1054 by 4Ω. This represents a significant
increase in the voltage losses. For C
less dramatic. C
at a current approximately equal to the output current and
the ESR of the capacitor will cause a step function to oc-
cur in the output ripple at the switch transitions. This step
function will degrade the output regulation for changes
in output load current and should be avoided. Realizing
that large value tantalum capacitors can be expensive, a
technique that can be used is to parallel a smaller tantalum
capacitor with a large aluminum electrolytic capacitor to
gain both low ESR and reasonable cost. Where physical
size is a concern some of the newer chip type surface
mount tantalum capacitors can be used. These capacitors
are normally rated at working voltages in the 10V to 20V
range and exhibit very low ESR (in the range of 0.1Ω).
Output Ripple
The peak-to-peak output ripple is determined by the value
of the output capacitor and the output current. Peak-to-
peak output ripple may be approximated by the formula:
dV =
2fC
I
OUT
OUT
IN
OUT
the effect of the ESR of the capacitor will
is alternately charged and discharged
OUT
the affect of ESR is
IN
and C
IN
and C
OUT
1054lff
OUT
are
IN