LTC3546IUFD#PBF Linear Technology, LTC3546IUFD#PBF Datasheet - Page 17

• 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

APPLICATIONS INFORMATION
density, but it has a larger ESR and it is critical that the
capacitors are surge tested for use in switching power
supplies. An excellent choice is the AVX TPS series of
surface tantalums, available in case heights ranging from
2mm to 4mm. Aluminum electrolytic capacitors have a
signifi cantly larger ESR, and are often used in extremely
cost-sensitive applications provided that consideration
is given to ripple current ratings and long term reliability.
Ceramic capacitors have the lowest ESR and cost but also
have the lowest capacitance density, high voltage and
temperature coeffi cient and exhibit audible piezoelectric
effects. In addition, the high Q of ceramic capacitors along
with trace inductance can lead to signifi cant ringing. Other
capacitor types include the Panasonic specialty polymer
(SP) capacitors.
Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Because the
LTC3546 control loop does not depend on the output
capacitor’s ESR for stable operation, ceramic capacitors
can be used freely to achieve very low output ripple and
small circuit size. When choosing the input and output
ceramic capacitors, choose the X5R or X7R dielectric
formulations. These dielectrics have the best temperature
and voltage characteristics of all the ceramics for a given
value and size.
Great care must be taken when using only ceramic input
and output capacitors. 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
couple to the output and be mistaken as loop instability.
At worst, the ringing at the input can be large enough to
disrupt circuit operation or 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
IN
pin. At best, this ringing can
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, 3 to 4
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
droop 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 impedance to
the supply is very low. A 10μF ceramic capacitor is usually
enough for these conditions.
Setting the Output Voltage
The LTC3546 generates a 0.6V reference voltage between
the feedback pin, V
The output voltage is set by a resistive divider according
to the following formula:
Resistor locations are shown in Figure 2.
C
V
V
OUT
OUT1
OUT2
DROOP
C
FF1
2.5
0.6V 1+
0.6V 1+
Figure 2. Setting Output Voltages
V
f
, is usually about 2 to 3 times the linear
O
OUT1
V
DROOP
I
OUT
R1
R2
FB1
R2
R1
R4
R3
V
and V
FB1
LTC3546
FB2
V
3546 F02
FB2
, and the signal ground.
R3
R4
V
LTC3546
OUT2
C
FF2
17
3546fb