Datasheet
Table Of Contents
- FEATURES
- APPLICATIONS
- DESCRIPTION
- ABSOLUTE MAXIMUM RATINGS
- OPERATING RATINGS
- ELECTRICAL CHARACTERISTICS
- TYPICAL PERFORMANCE CHARACTERISTICS
- BLOCK DIAGRAM
- OPERATION DESCRIPTION
- GENERAL
- PRECISION ENABLE
- PEAK CURRENT MODE CONTROL
- CURRENT LIMIT
- SOFT-START AND VOLTAGE TRACKING
- PRE-BIAS START UP CAPABILITY
- POWER GOOD AND OVER VOLTAGE FAULT HANDLING
- UVLO
- THERMAL PROTECTION
- LIGHT LOAD OPERATION
- Design Guide
- INDUCTOR SELECTION (L)
- OUTPUT CAPACITOR SELECTION (COUT)
- INPUT CAPACITOR SELECTION (CIN)
- SETTING THE OUTPUT VOLTAGE (RFB1, RFB2)
- LOOP COMPENSATION (RC1, CC1)
- AVIN FILTERING COMPONENTS (CF and RF)
- SUB-REGULATOR BYPASS CAPACITOR (CVCC)
- SETTING THE START UP TIME (CSS)
- USING PRECISION ENABLE AND POWER GOOD
- TRACKING AN EXTERNAL SUPPLY
- THERMAL CONSIDERATIONS
- PCB LAYOUT CONSIDERATIONS
- Typical Application Circuit
- Bill of Materials (VIN = 5V, VOUT = 3.3V, IOUTMAX = 3A)
- Bill of Materials (VIN = 3.3V to 5V, VOUT = 1.2V, IOUTMAX = 3A)
- Revision History
PVIN
SW
AGND
FB
PGOOD
EN
SS/TRK
AVIN
COMP
LM20123
L
R
F
VCC
PGND
C
IN
R
C1
C
C1
V
IN
C
SS
C
VCC
C
OUT
V
OUT
R
FB2
R
FB1
C
F
(optional)
LM20123
SNVS524E –OCTOBER 2007–REVISED MARCH 2013
www.ti.com
Typical Application Circuit
This section provides several application solutions with a bill of materials. All bill of materials reference the below
figure. The compensation for these solutions were optimized to work over a wide range of input and output
voltages; if a faster transient response is needed reduce the value of C
C1
and calculate the new value for R
C1
as
outline in the design guide.
Bill of Materials (V
IN
= 5V, V
OUT
= 3.3V, I
OUTMAX
= 3A)
Designator Description Part Number Manufacturer Qty
U1 Synchronous Buck Regulator LM20123 Texas Instruments 1
C
IN
47 µF, 1210, X5R, 6.3V GRM32ER60J476ME20 Murata 1
C
OUT
47 µF, 1210, X5R, 6.3V GRM32ER60J476ME20 Murata 1
L 1.2 µH, 17 mΩ DO1813H-122ML Coilcraft 1
R
F
1Ω, 0603 CRCW06031R0J-e3 Vishay-Dale 1
C
F
100 nF, 0603, X7R, 16V GRM188R71C104KA01 Murata 1
C
VCC
1 µF, 0603, X5R, 6.3V GRM188R60J105KA01 Murata 1
R
C1
8.45 kΩ, 0603 CRCW06038451F-e3 Vishay-Dale 1
C
C1
1.5 nF, 0603, X7R, 25V VJ0603Y152KXXA Vishay-Vitramon 1
C
SS
33 nF, 0603, X7R, 25V VJ0603Y333KXXA Vishay-Vitramon 1
R
FB1
31.6 kΩ, 0603 CRCW06033162F-e3 Vishay-Dale 1
R
FB2
10.2 kΩ, 0603 CRCW06031022F-e3 Vishay-Dale 1
Bill of Materials (V
IN
= 3.3V to 5V, V
OUT
= 1.2V, I
OUTMAX
= 3A)
Designator Description Part Number Manufacturer Qty
U1 Synchronous Buck Regulator LM20123 Texas Instrumentsn 1
C
IN
47 µF, 1210, X5R, 6.3V GRM32ER60J476ME20 Murata 1
C
OUT
47 µF, 1210, X5R, 6.3V GRM32ER60J476ME20 Murata 1
L 0.68 µH, 5 mΩ IHLP2525CZER0R68M01 Vishay 1
R
F
1Ω, 0603 CRCW06031R0J-e3 Vishay-Dale 1
C
F
100 nF, 0603, X7R, 16V GRM188R71C104KA01 Murata 1
C
VCC
1 µF, 0603, X5R, 6.3V GRM188R60J105KA01 Murata 1
R
C1
5.76 kΩ, 0603 CRCW06035761F-e3 Vishay-Dale 1
C
C1
2.2 nF, 0603, X7R, 25V VJ0603Y222KXXA Vishay-Vitramon 1
C
SS
33 nF, 0603, X7R, 25V VJ0603Y333KXXA Vishay-Vitramon 1
R
FB1
4.99 kΩ, 0603 CRCW06034991F-e3 Vishay-Dale 1
R
FB2
10 kΩ, 0603 CRCW06031002F-e3 Vishay-Dale 1
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