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PDF LT1931A Data sheet ( Hoja de datos )
| Número de pieza | LT1931A | |
| Descripción | 1.2MHz/2.2MHz Inverting DC/DC Converters in ThinSOT | |
| Fabricantes | Linear Technology | |
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LT1931/LT1931A
1.2MHz/2.2MHz Inverting
DC/DC Converters in ThinSOT
FEATURES
s Fixed Frequency 1.2MHz/2.2MHz Operation
s Very Low Noise: 1mVP-P Output Ripple
s – 5V at 350mA from 5V Input
s –12V at 150mA from 5V Input
s Uses Small Surface Mount Components
s Wide Input Range: 2.6V to 16V
s Low Shutdown Current: <1µA
s Low VCESAT Switch: 400mV at 1A
s Low Profile (1mm) ThinSOTTM Package
s Pin-for-Pin Compatible with the LT1611
U
APPLICATIO S
s Disk Drive MR Head Bias
s Digital Camera CCD Bias
s LCD Bias
s GaAs FET Bias
s Local Low Noise/Low Impedance Negative Supply
DESCRIPTIO
The LT®1931/LT1931A are the industry’s highest power
inverting SOT-23 current mode DC/DC converters. Both
parts include a 1A integrated switch allowing high current
outputs to be generated in a small footprint. The LT1931
switches at 1.2MHz while the LT1931A switches at 2.2MHz.
These high speeds enable the use of tiny, low cost
capacitors and inductors 2mm or less in height. The
LT1931 is capable of generating – 5V at 350mA or –12V
at 150mA from a 5V supply, while the LT1931A can
generate –5V at 300mA using significantly smaller induc-
tors. Both parts are easy pin-for-pin upgrades for higher
power LT1611 applications.
The LT1931/LT1931A operate in a dual inductor inverting
topology that filters both the input side and output side
current. Very low output voltage ripple approaching 1mVP-P
can be achieved when ceramic output capacitors are used.
Fixed frequency switching ensures a clean output free
from low frequency noise typically present with charge
pump solutions. The low impedance output remains within
1% of nominal during large load steps. The 36V switch
allows VIN to VOUT differential of up to 34V.
The LT1931/LT1931A are available in the 5-lead ThinSOT
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
L1A
10µH
C2
1µF
5V
C1
4.7µF
VIN SW
SHDN
LT1931
NFB
GND
R1
29.4k
R2
10k
C4
220pF
L1B
10µH
D1
VOUT
–5V
350mA
C3
22µF
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R LMK212BJ105MG
C3: TAIYO YUDEN X5R JMK325BJ226MM
D1: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-100
1931 F01
Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter
Efficiency
100
95
90
85
80
75
70
65
60
55
50
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
1931 TA01
1
1 page  
LT1931/LT1931A
APPLICATIO S I FOR ATIO
LT1931A AND LT1931 DIFFERENCES:
Switching Frequency
The key difference between the LT1931A and LT1931 is
the faster switching frequency of the LT1931A. At 2.2MHz,
the LT1931A switches at nearly twice the rate of the
LT1931. Care must be taken in deciding which part to use.
The high switching frequency of the LT1931A allows
smaller cheaper inductors and capacitors to be used in a
given application, but with a slight decrease in efficiency
and maximum output current when compared to the
LT1931. Generally, if efficiency and maximum output
current are critical, the LT1931 should be used. If applica-
tion size and cost are more important, the LT1931A will be
the better choice. In many applications, tiny inexpensive
chip inductors can be used with the LT1931A, reducing
solution cost.
Duty Cycle
The maximum duty cycle (DC) of the LT1931A is 75%
compared to 84% for the LT1931. The duty cycle for a
given application using the dual inductor inverting topol-
ogy is given by:
DC = | VOUT |
| VIN | + | VOUT |
For a 5V to –5V application, the DC is 50% indicating that
the LT1931A can be used. A 5V to –16V application has a
DC of 76.2% making the LT1931 the right choice. The
LT1931A can still be used in applications where the DC, as
calculated above, is above 75%. However, the part must
be operated in the discontinuous conduction mode so that
the actual duty cycle is reduced.
INDUCTOR SELECTION
Several inductors that work well with the LT1931 are listed
in Table 1 and those for the LT1931A are listed in Table 2.
Besides these, there are many other inductors that can be
used. Consult each manufacturer for detailed information
and for their entire selection of related parts. Ferrite core
inductors should be used to obtain the best efficiency, as
core losses at frequencies above 1MHz are much lower for
ferrite cores than for powdered-iron units. When using
coupled inductors, choose one that can handle at least 1A
of current without saturating, and ensure that the inductor
has a low DCR (copper-wire resistance) to minimize I2R
power losses. If using uncoupled inductors, each inductor
need only handle one-half of the total switch current so
that 0.5A per inductor is sufficient. A 4.7µH to 15µH
coupled inductor or a 15µH to 22µH uncoupled inductor
will usually be the best choice for most LT1931 designs.
For the LT1931A, a 2.2µH to 4.7µH coupled inductor or a
3.3µH to 10µH uncoupled inductor will usually suffice. In
certain applications such as the “Charge Pump” inverting
DC/DC converter, only a single inductor is used. In this
case, the inductor must carry the entire 1A switch current.
Table 1. Recommended Inductors—LT1931
PART
L Size
(µH) (L × W × H) mm VENDOR
CLS62-100
CR43-150
CR43-220
10 6.8 × 6.6 × 2.5 Sumida
15 4.5 × 4.0 × 3.2 (847) 956-0666
22 www.sumida.com
CTX10-1
CTX15-1
10 8.9 × 11.4 × 4.2 Coiltronics
15 (407) 241-7876
www. coiltronics.com
LQH3C100K24
LQH4C150K04
10 3.2 × 2.5 × 2.0 Murata
15 (404) 436-1300
www.murata.com
Table 2. Recommended Inductors—LT1931A
PART
L Size
(µH) (L × W × H) mm VENDOR
ELJPC3R3MF
ELJPC4R7MF
3.3 2.5 × 2.0 × 1.6 Panasonic
4.7 (408) 945-5660
www.panasonic.com
CLQ4D10-4R71
CLQ4D10-6R82
4.7 7.6 × 4.8 × 1.8 Sumida
6.8 (847) 956-0666
www.sumida.com
LB20164R7M
LB20163R3M
4.7 2.0 × 1.6 × 1.6 Taiyo Yuden
3.3 (408) 573-4150
www.t-yuden.com
LQH3C4R7K24
LQH4C100K24
4.7
10
1Use drawing #5382-T039
2Use drawing #5382-T041
3.2 × 2.5 × 2.0
Murata
(404) 436-1300
www.murata.com
5
5 Page 
LT1931/LT1931A
TYPICAL APPLICATIO S
SLIC Power Supply with – 21.6V and – 65V Outputs, Uses Soft-Start
VIN
5V
RSS
15k
VSS
L1
10µH
C1
4.7µF
16V VIN
SW
CSS
68nF
LT1931
SHDN
NFB
GND
R2
1k
R1
1Ω
R3
16.2k
C8
1000pF R4
2.7k
*TOTAL OUTPUT POWER NOT TO EXCEED 1.3W
C1 TO C7: X5R OR X7R
D1, D2: BAV99 OR EQUIVALENT
L1: SUMIDA CR43-100
C4
1µF
35V
C2
1µF
35V
D1
32
1
C3
1µF
35V
D2
32
1
D3
32
1
C5
4.7µF
25V
COM
VOUT1
–21.6V
48mA*
C6
4.7µF
25V
C7
4.7µF
25V VOUT2
– 65V
1931 TA09 20mA*
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
(LTC DWG # 05-08-1635)
2.80 – 3.10
(.110 – .118)
(NOTE 3)
.20
(.008)
DATUM ‘A’
A A2
L
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
.09 – .20
(.004 – .008)
(NOTE 2)
2.
DIMENSIONS
ARE
IN
MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
4. DIMENSIONS ARE INCLUSIVE OF PLATING
5. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
6. MOLD FLASH SHALL NOT EXCEED .254mm
7. PACKAGE EIAJ REFERENCE IS:
SC-74A (EIAJ) FOR ORIGINAL
JEDEL MO-193 FOR THIN
1.90
(.074)
REF
SOT-23
(Original)
A
.90 – 1.45
(.035 – .057)
A1
.00 – .15
(.00 – .006)
A2
.90 – 1.30
(.035 – .051)
L
.35 – .55
(.014 – .021)
SOT-23
(ThinSOT)
1.00 MAX
(.039 MAX)
.01 – .10
(.0004 – .004)
.80 – .90
(.031 – .035)
.30 – .50 REF
(.012 – .019 REF)
2.60 – 3.00
(.102 – .118)
1.50 – 1.75
(.059 – .069)
(NOTE 3)
A1
PIN ONE
.95
(.037)
REF
.25 – .50
(.010 – .020)
(5PLCS, NOTE 2)
S5 SOT-23 0501
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LT1931A.PDF ] | |
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