SC121ULTRT Semtech, SC121ULTRT Datasheet - Page 19

• Manufacturer Part Number: SC121ULTRT
• Description: IC BOOST SYNC 1.2A MLPD-6
• Manufacturer: Semtech
• Type: Step-Up (Boost)r

Specifications of SC121ULTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 1.8 ~ 5 V
• Current - Output: 1.2A
• Frequency - Switching: 1.2MHz
• Voltage - Input: 0.7 ~ 4.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 6-MLPD-UT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC121ULTRTTR

Applications Information (continued)
Note that this is a negative quantity, since V
0 < D < 1. For a constant load in steady-state, the inductor
current must satisfy ΔI
expressions and solving for D, obtain D = 1 – V
Using this expression, and the positive valued expression
ΔI
expression for I
From this result, obtain an alternative expression for ΔI
The inductor selection should consider the n-channel FET
current limit for the expected range of input voltage and
output load current. The largest I
expected smallest V
largest expected ΔI
ensure that the n-channel FET current limit is not exceed.
That is, for the minimum n-channel FET current limit,
worst case inductor tolerance, highest expected output
current, and lowest expected V
Many of these equations include the parameter η, effi -
ciency. Effi ciency varies with V
Estimate η using the plots provided in this datasheet, or
from experimental data, at the operating condition of
interest.
Any chosen inductor should have low DCR compared to
the R
though for DCR << R
provide diminishing benefi t. The inductor I
exceed the expected I
quency should exceed 5×f
properties should provide satisfactory performance.
L = 4.7μH should perform well for most applications.
The following table lists the manufacturers of recom-
mended inductor options. The specifi cation values shown
are simplifi ed approximations or averages of many device
parameters under various test conditions. See manufac-
turers’ documentation for full performance data.
L
= ΔI
I
I
L
L-max
I
DS-ON
max,min
L
L-on
I
= I
L
for current ripple amplitude, obtain expanded
of the FET switches to maintain efficiency,
max
L-avg
V
OUT
V
L-max
I
+ ΔI
IN
L
min
I
and I
OUT
L
L
. Then for the largest expected I
/2 < I
IN
DS-ON
L-max
L-on
T
L
and largest I
L-min
2
+ ΔI
. The inductor self-resonant fre-
, further reduction in DCR will
T
V
LIM(N)
V
.
L
osc
OUT
IN
L-off
. Any inductor with these
.
IN
V
V
= 0. Substituting the two
, ensure that
IN
OUT
IN
V
, I
OUT
OUT
L-avg
OUT
V
, and temperature.
OUT
. Determine the
V
will occur at the
IN
SAT
V
value should
OUT
IN
> V
IN
IN
/V
and
L-avg
OUT
L
.
.
,
Capacitor Selection
Input and output capacitors must be chosen carefully to
ensure that they are of the correct value and rating. The
output capacitor requires a minimum capacitance value
of 10μF at the programmed output voltage to ensure sta-
bility over the full operating range. This must be consid-
ered when choosing small package size capacitors as the
DC bias must be included in their derating to ensure this
required value. For example, a 10μF 0805 capacitor may
provide suffi cient capacitance at low output voltages but
may be too low at higher output voltages. Therefore, a
higher capacitance value may be required to provide the
minimum of 10μF at these higher output voltages.
Low ESR capacitors such as X5R or X7R type ceramic
capacitors are recommended for input bypassing and
output filtering. Low-ESR tantalum capacitors are not
recommended due to possible reduction in capacitance
seen at the switching frequency of the SC121. Ceramic
capacitors of type Y5V are not recommended as their tem-
perature coeffi cients make them unsuitable for this appli-
cation. The following table lists recommended capacitors.
For smaller values and smaller packages, it may be neces-
sary to use multiples devices in parallel.
Manufacturer/
Part #
Murata
LQM31PN4R7M00
Coilcraft
XFL2006-472
Manufacturer/
Part Number
Murata
GRM21BR60J226ME39B
Murata
GRM31CR71A226KE15L
Murata
GRM185R60G475ME15
TDK
C2012X5R1A226M
Taiyo Yuden
JMK212BJ226MG-T
Value
(μH)
4.7
4.7
Value
(μF)
4.7
22
22
22
22
DCR
(Ω)
0.3
0.7
Rated Volt-
age (VDC)
Current
Rated
6.3
10
10
20
(mA)
4
700
500
Tolerance
Type
X5R
X7R
X5R
X5R
X5R
(%)
20
20
Case
0805
1206
0603
0805
0805
Size
3.2 x 1.6 x 0.95
SC121
Dimensions
2 x 2 x 0.6
LxWxH
(mm)
Height
(mm)
Case
1.25
0.85
1.25
1.6
0.5
19