LTC3615EFE-1#TRPBF Linear Technology, LTC3615EFE-1#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC3615EFE-1#TRPBF
• Description: IC REG SYNC BUCK 3A 24TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3615EFE-1#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5.5 V
• Current - Output: 3A
• Frequency - Switching: 400kHz ~ 4MHz
• Voltage - Input: 2.25 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP Exposed Pad, 24-eTSSOP, 24-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC3615/LTC3615-1
APPLICATIONS INFORMATION
Output Capacitor C
The selection of C
ESR to minimize voltage ripple and load step transients
(low-ESR ceramic capacitors are discussed in the next
section). Typically, once the ESR requirement is satisfi ed,
the capacitance is adequate for fi ltering. The output ripple
ΔV
where f
and ΔI
is highest at maximum input voltage since ΔI
with input voltage.
In surface mount applications, multiple capacitors may
have to be paralleled to meet the capacitance, ESR or RMS
current handling requirement of the application. Aluminum
electrolytic, special polymer, ceramic and dry tantalum
capacitors are all available in surface mount packages.
Tantalum capacitors have the highest capacitance density,
but can have higher ESR and must be surge tested for
use in switching power supplies. Aluminum electrolytic
capacitors have signifi cantly higher ESR, but can often
be used in extremely cost-sensitive applications provided
that consideration is given to ripple current ratings and
long term reliability.
Ceramic Input and Output Capacitors
Ceramic capacitors have the lowest ESR and can be cost
effective, but also have the lowest capacitance density,
high voltage and temperature coeffi cients, and exhibit
audible piezoelectric effects. In addition, the high-Q of
ceramic capacitors along with trace inductance can lead
to signifi cant ringing.
18
OUT
Δ
V
OUT
L
is determined by:
SW
= ripple current in the inductor. The output ripple
= operating frequency, C
≤
Δ
I
L
•
⎛
⎜
⎝
OUT
ESR
OUT
is typically driven by the required
+
Selection
8
•
f
SW
1
•
OUT
C
OUT
= output capacitance
⎞
⎟
⎠
L
increases
Capacitors are tempting for switching regulator use
because of their very low ESR. Great care must be taken
when using only ceramic input and output capacitors.
Ceramic caps are prone to temperature effects which re-
quire the designer to check loop stability over the operating
temperature range. To minimize their large temperature and
voltage coeffi cients, only X5R or X7R ceramic capacitors
should be used.
When a ceramic capacitor is used at the input, and the
power is being supplied through long wires, such as from
a wall adapter, a load step at the output can induce ringing
at the V
and be mistaken as loop instability. At worst, the ringing
at the input can be large enough to damage the part.
Since the ESR of a ceramic capacitor is so low, the input
and output capacitor must instead fulfi ll a charge storage
requirement. During a load step, the output capacitor must
instantaneously supply the current to support the load
until the feedback loop raises the switch current enough
to support the load. The time required for the feedback
loop to respond is dependent on the compensation com-
ponents and the output capacitor size. Typically, three to
four cycles are required to respond to a load step, but only
in the fi rst cycle does the output drop linearly. The output
droop, V
linear drop of the fi rst cycle. Thus, a good place to start
is with the output capacitor size of approximately:
More capacitance may be required depending on the duty
cycle and load step requirements. In most applications,
the input capacitor is merely required to supply high
frequency bypassing, since the impedance to the supply
is very low.
C
OUT
IN
DROOP
≈
pin. At best, this ringing can couple to the output
f
SW
2 5 . •
, is usually about two to three times the
•
V
Δ
DROOP
I
OUT
3615fa