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Teilenummer | LD1117A |
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Beschreibung | Low drop fixed and adjustable positive voltage regulators | |
Hersteller | ST Microelectronics | |
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Gesamt 24 Seiten LD1117A
Low drop fixed and adjustable positive voltage regulators
Datasheet - production data
SOT-223
• Available in ± 2% (at 25 °C) and 4% in full
temperature range
• High supply voltage rejection:
– 80 dB typ. (at 25 °C)
• Temperature range: 0 °C to 125 °C
TO-220
Description
DPAK
Features
• Low dropout voltage:
– 1.15 V typ. @ IOUT = 1 A, 25 °C
• Very low quiescent current:
– 5 mA typ. @ 25 °C
• Output current up to 1 A
The LD1117A is a low drop voltage regulator able
to provide up to 1 A of output current, available
also in adjustable versions (VREF = 1.25 V). In
fixed versions, the following output voltages are
offered: 1.2 V, 1.8 V, and 3.3 V. The device is
supplied in: SOT-223, DPAK and TO-220. Surface
mounted packages optimize the thermal
characteristics while offering a relevant space
saving advantage. High efficiency is assured by
an NPN pass transistor. Only a very common 10
µF minimum capacitor is needed for stability. Chip
trimming allows the regulator to reach a very tight
output voltage tolerance, within ± 2% at 25 °C.
• Fixed output voltage of:
– 1.2 V, 1.8 V, 3.3 V
• Adjustable version availability (VREF = 1.25 V)
• Internal current and thermal limit
• Only 10 µF for stability
Table 1. Device summary
SOT-223
Order codes
DPAK
TO-220
Output voltage
LD1117AS12TR
LD1117AS18TR
LD1117AS33TR
LD1117ASTR
LD1117ADT12TR
LD1117ADT18TR
LD1117ADT33TR
LD1117ADT-TR
LD1117AV33
1.2 V
1.8 V
3.3 V
Adjustable from 1.25 V
July 2013
This is information on a product in full production.
DocID7194 Rev 26
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www.st.com
Schematic application
4 Schematic application
Figure 3. Application circuit (for fixed output voltages)
A
LD1117A
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6 Page LD1117A adjustable: application note
7 LD1117A adjustable: application note
LD1117A
The LD1117A adjustable has a thermal stabilized 1.25 ± 0.012 V reference voltage between
the OUT and ADJ pins. IADJ is 60 µA typ. (120 µA max.) and ΔIADJ is 1 µA typ. (5 µA max.).
R1 is normally fixed to 120 Ω. From Figure 6 the following is obtained:
VOUT = VREF + R2 (IADJ + IR1) = VREF + R2 (IADJ +VREF /R1) = VREF (1 + R2 / R1) + R2 x
IADJ.
In normal applications the R2 value is in the range of a few kΩ, so the R2 x IADJ product can
not be considered in the VOUT calculation; the above expression then becomes:
VOUT = VREF (1 + R2 / R1).
In order to have a better load regulation it is important to realize a good Kelvin connection of
R1 and R2 resistors. In particular, the R1 connection must be realized very close to the OUT
and ADJ pins, while the R2 ground connection must be placed as near as possible to the
negative load pin. Ripple rejection can be improved by introducing a 10 µF electrolytic
capacitor placed in parallel to the R2 resistor (see Figure 8).
Figure 8. Adjustable output voltage application
LD1117A
Figure 9. Adjustable output voltage application with improved ripple rejection
LD1117A
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12 Page | ||
Seiten | Gesamt 24 Seiten | |
PDF Download | [ LD1117A Schematic.PDF ] |
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