LT3470AEDDB#TRMPBF Linear Technology, LT3470AEDDB#TRMPBF Datasheet - Page 10

• Manufacturer Part Number: LT3470AEDDB#TRMPBF
• Description: IC BUCK ADJ .25A 8DFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3470AEDDB#TRMPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.25 ~ 16 V
• Current - Output: 250mA
• Voltage - Input: 4 ~ 40 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -

APPLICATIONS INFORMATION
LT3470A
Input Capacitor
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
at the V
current into a tight local loop, minimizing EMI. The input
capacitor must have low impedance at the switching
frequency to do this effectively. A 1μF to 2.2μF ceramic
capacitor satisfies these requirements.
If the input source impedance is high, a larger value ca-
pacitor may be required to keep input ripple low. In this
case, an electrolytic of 10μF or more in parallel with a 1μF
ceramic is a good combination. Be aware that the input
capacitor is subject to large surge currents if the LT3470A
circuit is connected to a low impedance supply, and that
some electrolytic capacitors (in particular tantalum) must
be specified for such use.
Output Capacitor and Output Ripple
The output capacitor filters the inductor’s ripple current
and stores energy to satisfy the load current when the
LT3470A is quiescent. In order to keep output voltage
ripple low, the impedance of the capacitor must be low at
the LT3470A’s switching frequency. The capacitor’s equiva-
lent series resistance (ESR) determines this impedance.
10
Table 2. Inductor Vendors
VENDOR
Coilcraft
Sumida
Toko
Würth Elektronik
Coiltronics
Murata
IN
pin of the LT3470A and to force this switching
URL
www.coilcraft.com
www.sumida.com
www.tokoam.com
www.we-online.com
www.cooperet.com
www.murata.com
PART SERIES
DO1605
ME3220
DO3314
CR32
CDRH3D16/HP
CDRH3D28
CDRH2D18/HP
DB320C
D52LC
WE-PD2 Typ S
WE-TPC Typ S
SD10
LQH43C
LQH32C
Choose one with low ESR intended for use in switching
regulators. The contribution to ripple voltage due to the
ESR is approximately I
~150mΩ. The value of the output capacitor must be large
enough to accept the energy stored in the inductor without
a large change in output voltage. Setting this voltage step
equal to 1% of the output voltage, the output capacitor
must be:
Where I
cal Characteristics). For example, an LT3470A producing
3.3V with L = 33μH requires 22μF . The calculated value
can be relaxed if small circuit size is more important than
low output ripple.
Sanyo’s POSCAP series in B-case and provides very good
performance in a small package for the LT3470A. Similar
performance in traditional tantalum capacitors requires
a larger package (C-case). With a high quality capacitor
filtering the ripple current from the inductor, the output
voltage ripple is determined by the delay in the LT3470A’s
feedback comparator. This ripple can be reduced further
by adding a small (typically 22pF) phase lead capacitor
between the output and the feedback pin.
C
OUT
INDUCTANCE RANGE (μH)
10 to 47
10 to 47
10 to 47
10 to 47
10 to 33
10 to 47
10 to 15
10 to 27
10 to 47
10 to 47
10 to 22
10 to 47
10 to 47
10 to 15
LIM
> 50 • L •
is the top current limit with V
⎛
⎜
⎝
V
I
LIM
OUT
LIM
⎞
⎟
⎠
• ESR. ESR should be less than
2
SIZE (mm)
1.8 × 5.4 × 4.2
2.0 × 3.2 × 2.5
1.4 × 3.3 × 3.3
3.0 × 3.8 × 4.1
1.8 × 4.0 × 4.0
3.0 × 4.0 × 4.0
2.0 × 3.2 × 3.2
2.0 × 3.8 × 3.8
2.0 × 5.0 × 5.0
3.2 × 4.0 × 4.5
1.6 × 3.8 × 3.8
1.0 × 5.0 × 5.0
2.6 × 3.2 × 4.5
1.6 × 2.5 × 3.2
FB
= 0V (see Electri-
3470afb