LM2853MHX-1.8/NOPB National Semiconductor, LM2853MHX-1.8/NOPB Datasheet - Page 9

• Manufacturer Part Number: LM2853MHX-1.8/NOPB
• Description: IC REG SYNC BUCK 3A 1.8V 14TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®, SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2853MHX-1.8/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.8V
• Current - Output: 3A
• Frequency - Switching: 550kHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 14-TSSOP Exposed Pad, 14-eTSSOP 14-HTSSOP
• For Use With: LM2853-1.8EVAL - BOARD EVAL LM2853-1.8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM2853MHX-1.8

Applications Information
CHOOSING AN INDUCTANCE VALUE
The current ripple present in the output filter inductor is
determined by the input voltage, output voltage, switching
frequency and inductance according to the following equa-
tion:
where ∆I
cycle V
stage, V
switching frequency and L
filter inductor. Knowing the current ripple is important for
inductor selection since the peak current through the induc-
tor is the load current plus one half the ripple current. Care
must be taken to ensure the peak inductor current does not
reach a level high enough to trip the current limit circuitry of
the LM2853. As an example, consider a 5V to 1.2V conver-
sion and a 550 kHz switching frequency. According to Table
1, a 4.7 µH inductor may be used. Calculating the expected
peak-to-peak ripple,
OUTPUT FILTER CAPACITORS
The recommended capacitors that may be used in the output
filter with the LM2853 are limited in value and ESR range
according to Table 1.
Capacitance (µF)
OUT
OUT
L
Inductance
100
100
100
100
100
120
150
150
150
150
150
150
220
220
220
220
is the peak to peak current ripple, D is the duty
/V
4.7 µF
4.7 µF
4.7 µF
5.2 µF
5.6 µF
6.8 µF
6.8 µF
IN
is the output voltage of the switcher, f is the
, V
IN
is the input voltage applied to the output
O
is the inductance of the output
591D157X_6R3C2_20H
591D227X_6R3D2_20H
591D227X_010D2_20H
593D227X_6R3D2_E3
593D107X_010D2_E3
NOSD107M006#0080
NOSC107M004#0070
NOSD157M006#0070
TPSC107M006#0075
TPSD157M006#0050
TPSC157M004#0070
594D127X_6R3C2T
594D227X_6R3D2T
594D107X_010C2T
594D157X_010C2T
595D157X_010D2T
Part Number
TABLE 3. Recommended Capacitors
(Continued)
TABLE 2. Recommended Inductors
DO3308P-472ML
DO3316P-472ML
MSS1260-472ML
MSS1038-522NL
MSS1260-562ML
DO3316P-682ML
MSS1260-682ML
Part Number
9
The maximum inductor current for a 3A load would therefore
be 3A plus 177 mA, 3.177A. As shown in the ripple equation,
the current ripple is inversely proportional to inductance.
OUTPUT FILTER INDUCTORS
Once the inductance value is chosen, the key parameter for
selecting the output filter inductor is its saturation current
(I
turer as the current at which the inductance of the coil falls to
a certain percentage of the nominal inductance. The I
an inductor used in an application should be greater than the
maximum expected inductor current to avoid saturation. Be-
low is a table of inductors that are suitable in LM2853
applications.
Below are some examples of capacitors that can typically be
used in an LM2853 application.
Niobium Oxide
Niobium Oxide
Niobium Oxide
SAT
Chemistry
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
Tantalum
) specification. Typically I
SAT
Coilcraft
Coilcraft
Coilcraft
Coilcraft
Coilcraft
Coilcraft
Coilcraft
Vendor
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
Vishay-Sprague
is given by the manufac-
Vendor
AVX
AVX
AVX
AVX
AVX
AVX
www.national.com
SAT
of