LM26484SQEV National Semiconductor, LM26484SQEV Datasheet - Page 14

• Manufacturer Part Number: LM26484SQEV
• Description: BOARD EVALUATION FOR LM2684
• Manufacturer: National Semiconductor

Specifications of LM26484SQEV

• Main Purpose: DC/DC, Step Down with LDO
• Outputs And Type: 3, Non-Isolated
• Voltage - Output: 1V, 1.8V, 1V
• Current - Output: 2A, 2A, 1A
• Voltage - Input: 3 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM26484
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

www.national.com
I
I
SUGGESTED INDUCTORS AND THEIR SUPPLIERS
OUTPUT CAPACITOR SELECTION FOR SW1 AND SW2
A ceramic output capacitor of 10 µF, 6.3V is recommended
with an ESR of less than 500 mΩ.
Output ripple can be estimated from the vector sum of the
reactive (Capacitor) voltage component and the real (ESR)
voltage component of the output capacitor.
V
V
V
The output capacitor needs to be mounted as close as pos-
sible to the output pin of the device.
The output filter capacitor smooths out current flow from the
inductor to the load, helps maintain a steady output voltage
during transient load changes and reduces output voltage
ripple. These capacitors must be selected with sufficient ca-
pacitance and sufficiently low ESR to perform these functions.
Note that the output voltage ripple is dependent on the induc-
tor current ripple and the equivalent series resistance of the
output capacitor (ESR
dent as well as temperature dependent. The R
calculated with the applicable switching frequency and ambi-
ent temperature.
SAT
LPEAK
Inductor
L1 and L2
COUT
ROUT
PPOUT
Output Voltage Range
:
:
:
:
:
V
V
Inductor saturation current at operating tempera-
ture
Peak inductor current during worst case conditions
OUT
OUT
Estimated reactive output ripple
Estimated real output ripple
Estimated peak-to-peak output ripple
≥
< 2.0V
2.0V
Value
0.5
COUT
). ESR
COUT
Unit
µH
30066106
Coilcraft
Coilcraft
Vendor
is frequency depen-
ESR
Description
SW1 and SW2 inductor
should be
LPS4012–222ML
LPS4414–501ML
14
Part Number
I
I
V
V
L:
F:
D:
EFF:
I
transients, startup, high temperature, worst case conditions,
etc.
INPUT CAPACITOR SELECTION FOR SW1 AND SW2
It is required to use a ceramic input capacitor of at least 10
μF and 6.3V with an ESR of less than 500 mΩ.
The input power source supplies average current continu-
ously. During the PFET switch on-time, however, the de-
manded di/dt is higher than can be typically supplied by the
input power source. This delta is supplied by the input capac-
itor.
A simplified “worst case” assumption is that all of the PFET
current is supplied by the input capacitor. This will result in
conservative estimates of input ripple voltage and capacitor
RMS current. Input ripple voltage is estimated as follows:
V
I
C
ESR
This capacitor is exposed to significant RMS current, so it is
important to select a capacitor with an adequate RMS current
rating. Capacitor RMS current estimated as follows:
I
OUTMAX
RIPPLE
SAT
OUT
RSCIN
OUT
IN
PPIN
IN:
:
:
may not be exceeded during any operation, including
IN:
:
:
:
: Maximum average inductor current
Estimated input capacitor RMS current
Estimated peak-to-peak input ripple voltage
Output current, Amps
Input capacitor value, Farads
Input capacitor ESR, Ohms
Peak-to-Peak inductor current
Output voltage
Input voltage
Inductor value in Henries at I
Switching frequency, Hertz
Estimated duty factor
Estimated power supply efficiency
2.2 µH
0.5 µH
Value
Notes
D.C.R. 50 mΩ
OUTMAX
DCR (max)
100 mΩ
50 mΩ