LTC3546IUFD#PBF Linear Technology, LTC3546IUFD#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC3546IUFD#PBF
• Description: IC BUCK SYNC ADJ 1A/2A DL 28QFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3546IUFD#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5 V
• Current - Output: 1A, 2A
• Frequency - Switching: 2.25MHz, 0.75MHz ~ 4MHz
• Voltage - Input: 2.25 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Dc To Dc Converter Type: Step Down
• Pin Count: 28
• Input Voltage: 5.5V
• Output Voltage: 0.6 to 5V
• Switching Freq: 750 TO 4000/2900KHz
• Output Current: 2A
• Efficiency: 96%
• Package Type: QFN EP
• Output Type: Adjustable
• Switching Regulator: Yes
• Load Regulation: 0.2%
• Line Regulation: 0.2%/V
• Mounting: Surface Mount
• Input Voltage (min): 2.25V
• Operating Temperature Classification: Automotive
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Compliant

LTC3546
APPLICATIONS INFORMATION
14
A general LTC3546 application circuit is shown in Figure 7.
External component selection is driven by the load require-
ment, and begins with the selection of the inductors L1,
and L2. Once L1 and L2 are chosen, C
can be selected.
Operating Frequency
Selection of the operating frequency is a trade-off between
effi ciency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves effi ciency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output ripple voltage.
The operating frequency, f
by pulling the FREQ pin to V
connecting an external resistor from FREQ to ground, or
by driving an external clock signal into SYNC/MODE.
When using an external resistor to set the oscillator fre-
quency use the following equation:
for 0.75MHz ≤ f
value for R
The maximum operating frequency is also constrained
by the minimum on-time (typically 70ns) and duty cycle,
especially when forced continuous mode is selected.
R
T
=
2.51•10
T
.
f
O
O
11
≤ 4MHz. Or use Figure 1 to select the
( )
Ω
– 20kΩ
O
, of the LTC3546 is determined
IN
, for 2.25MHz operation, by
IN
, C
OUT1
500
450
400
350
300
250
200
150
100
50
0
0
, and C
Figure 1. Frequency vs R
0.5
1.0
OUT2
FREQUENCY (MHz)
1.5
2.0
Assuming a worst-case minimum on-time of 150ns, this
can be calculated as:
The minimum frequency is limited by leakage and noise
coupling due to the large resistance of R
Inductor Selection
Although the inductor does not infl uence the operat-
ing frequency, the inductor value has a direct effect on
ripple current. The inductor ripple current ΔI
with higher inductance and increases with higher V
V
Accepting larger values of ΔI
tances, but results in higher output voltage ripple, greater
core losses, and lower output current capability.
A reasonable starting point for setting ripple current is ΔI
= 0.35I
current. The largest ripple ΔI
input voltage. To guarantee that the ripple current stays
below a specifi ed maximum, the inductor value should be
chosen according to the following equation:
2.5
OUT
L
f
3.0
O(MAX)
.
I
L
LOAD(MAX)
f
3.5
=
O
T
V
V
f
OUT
• I
O
4.0
OUT
• L
3546 F01
6.67
L
4.5
1
1
, where I
V
V
V
V
IN(MAX)
IN(MAX)
OUT
V
V
IN
OUT
OUT
LOAD(MAX)
L
(
allows the use of low induc-
MHz
L
occurs at the maximum
is the maximum output
)
T
.
L
decreases
IN
3546fb
or
L