Electronic Components Datasheet Search
  English  ▼
ALLDATASHEET.NET

X  

LT1945 Datasheet(PDF) 6 Page - Linear Technology

Part # LT1945
Description  Dual Micropower DC/DC Converter with Positive and Negative Outputs
Download  8 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LT1945 Datasheet(HTML) 6 Page - Linear Technology

  LT1945_15 Datasheet HTML 1Page - Linear Technology LT1945_15 Datasheet HTML 2Page - Linear Technology LT1945_15 Datasheet HTML 3Page - Linear Technology LT1945_15 Datasheet HTML 4Page - Linear Technology LT1945_15 Datasheet HTML 5Page - Linear Technology LT1945_15 Datasheet HTML 6Page - Linear Technology LT1945_15 Datasheet HTML 7Page - Linear Technology LT1945_15 Datasheet HTML 8Page - Linear Technology  
Zoom Inzoom in Zoom Outzoom out
 6 / 8 page
background image
LT1945
6
1945fa
Current Limit Overshoot
For the constant off-time control scheme of the LT1945,
the power switch is turned off only after the 350mA current
limit is reached. There is a 100ns delay between the time
when the current limit is reached and when the switch
actually turns off. During this delay, the inductor current
exceeds the current limit by a small amount. The peak
inductor current can be calculated by:
II
VV
L
ns
PEAK
LIM
IN MAX
SAT
=+
⎝⎜
⎠⎟
()
100
Where VSAT=0.25V(switchsaturationvoltage).Thecurrent
overshoot will be most evident for regulators with high input
voltages and smaller inductor values. This overshoot can
be beneficial as it helps increase the amount of available
output current for smaller inductor values. This will be the
peak current seen by the inductor (and the diode) during
normaloperation.Fordesignsusingsmallinductancevalues
(especially at input voltages greater than 5V), the current
limit overshoot can be quite high. Although it is internally
current limited to 350mA, the power switch of the LT1945
can handle larger currents without problem, but the overall
efficiency will suffer. Best results will be obtained when IPEAK
is kept below 700mA for the LT1945.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
be used at the output to minimize the output ripple voltage.
X5R or X7R multilayer ceramic capacitors are the best
choice, as they have a very low ESR and are available in
very small packages. Y5V ceramics are not recommended.
Their small size makes them a good companion to the
LT1945’s MS10 package. Solid tantalum capacitors (like
the AVX TPS, Sprague 593D families) or OS-CON capacitors
can be used, but they will occupy more board area than a
ceramic and will have a higher ESR. Always use a capacitor
with a sufficient voltage rating.
Ceramic capacitors also make a good choice for the input
decoupling capacitor, which should be placed as close
as possible to the LT1945. A 4.7μF input capacitor is
sufficient for most applications. Table 2 shows a list of
severalcapacitormanufacturers.Consultthemanufacturers
for more detailed information and for their entire selection
APPLICATIONS INFORMATION
Inductor Selection—Inverting Regulator
The formula below calculates the appropriate inductor value
to be used for an inverting regulator using the LT1945 (or
at least provides a good starting point). This value provides
a good tradeoff in inductor size and system performance.
Pick a standard inductor close to this value (both inductors
should be the same value). A larger value can be used to
slightly increase the available output current, but limit it to
around twice the value calculated below, as too large of an
inductance will increase the output voltage ripple without
providing much additional output current. A smaller value
can be used (especially for systems with output voltages
greater than 12V) to give a smaller physical size. Inductance
can be calculated as:
L
VV
I
t
OUT
D
LIM
OFF
=
+
2
where VD = 0.4V (Schottky diode voltage), ILIM = 350mA
and tOFF = 400ns.
For higher output voltages, the formula above will give
large inductance values. For a 2V to 20V converter (typical
LCD bias application), a 47μH inductor is called for with the
above equation, but a 10μH or 22μH inductor could be used
without excessive reduction in maximum output current.
Inductor Selection—Inverting Charge Pump Regulator
For the inverting regulator, the voltage seen by the internal
power switch is equal to the sum of the absolute value of
the input and output voltages, so that generating high output
voltages from a high input voltage source will often exceed
the 36V maximum switch rating. For instance, a 12V to –30V
converter using the inverting topology would generate 42V
on the SW pin, exceeding its maximum rating. For this ap-
plication, an inverting charge pump is the best topology.
The formula below calculates the approximate inductor
value to be used for an inverting charge pump regulator
using the LT1945. As for the boost inductor selection,
a larger or smaller value can be used. For designs with
varying VIN such as battery powered applications, use the
minimum VIN value in the equation below.
L
VV
V
I
t
OUT
IN MIN
D
LIM
OFF
=
−+
()


Similar Part No. - LT1945_15

ManufacturerPart #DatasheetDescription
logo
Linear Technology
LT1945EMS LINER-LT1945EMS Datasheet
142Kb / 8P
   Dual Micropower DC/DC Converter with Positive and Negative Outputs
More results

Similar Description - LT1945_15

ManufacturerPart #DatasheetDescription
logo
Linear Technology
LT1945 LINER-LT1945 Datasheet
142Kb / 8P
   Dual Micropower DC/DC Converter with Positive and Negative Outputs
logo
Texas Instruments
TPS65130 TI-TPS65130 Datasheet
550Kb / 29P
[Old version datasheet]   POSITIVE AND NEGATIVE OUTPUT DC-DC CONVERTER
TPS65130RGER TI1-TPS65130RGER Datasheet
1Mb / 34P
[Old version datasheet]   POSITIVE AND NEGATIVE OUTPUT DC-DC CONVERTER
TPS65130 TI1-TPS65130_16 Datasheet
1Mb / 32P
[Old version datasheet]   Positive and Negative Output DC-DC Converter
TPS65130RGER TI-TPS65130RGER Datasheet
1Mb / 34P
[Old version datasheet]   POSITIVE AND NEGATIVE OUTPUT DC-DC CONVERTER
TPS65131-Q1 TI1-TPS65131-Q1 Datasheet
1Mb / 33P
[Old version datasheet]   Positive- and Negative-Output DC-DC Converter
TPS65130 TI-TPS65130_15 Datasheet
1Mb / 32P
[Old version datasheet]   TPS6513x Positive and Negative Output DC-DC Converter
logo
Maxim Integrated Produc...
MAX685 MAXIM-MAX685_V01 Datasheet
350Kb / 11P
   Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD
2003
logo
TOKO, Inc
TK11835 TOKO-TK11835 Datasheet
13Kb / 1P
   POSITIVE TO NEGATIVE DC-DC CONVERTER
TK11830 TOKO-TK11830 Datasheet
85Kb / 13P
   POSITIVE-TO-NEGATIVE DC-DC CONVERTER
More results


Html Pages

1 2 3 4 5 6 7 8


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.NET
Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Contact us   |   Privacy Policy   |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com