LT3493EDCB#PBF Linear Technology, LT3493EDCB#PBF Datasheet - Page 11

• Manufacturer Part Number: LT3493EDCB#PBF
• Description: IC, STEP-DOWN PWM DC/DC CONVERTER, DFN-6
• Manufacturer: Linear Technology

Specifications of LT3493EDCB#PBF

• Primary Input Voltage: 36V
• No. Of Outputs: 1
• Output Current: 1.2A
• No. Of Pins: 6
• Operating Temperature Range: -40°C To +85°C
• Supply Voltage Range: 3.6V To 36V
• Switching Frequency Max: 815kHz
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
capacitor must be large to achieve low ESR. Table 2 lists
several capacitor vendors.
Figure 4 shows the transient response of the LT3493 with
several output capacitor choices. The output is 3.3V. The
load current is stepped from 250mA to 1A and back to
250mA, and the oscilloscope traces show the output volt-
age. The upper photo shows the recommended value. The
second photo shows the improved response (less voltage
drop) resulting from a larger output capacitor and a phase
lead capacitor. The last photo shows the response to a high
performance electrolytic capacitor. Transient performance
is improved due to the large output capacitance.
BOOST Pin Considerations
Capacitor C3 and diode D2 are used to generate a boost
voltage that is higher than the input voltage. In most cases
a 0.1μF capacitor and fast switching diode (such as the
1N4148 or 1N914) will work well. Figure 5 shows two
ways to arrange the boost circuit. The BOOST pin must
be at least 2.3V above the SW pin for best effi ciency. For
outputs of 3.3V and above, the standard circuit (Figure 5a)
is best. For outputs between 3V and 3.3V, use a 0.22μF
capacitor. For outputs between 2.5V and 3V, use a 0.47μF
capacitor and a small Schottky diode (such as the BAT-
54). For lower output voltages the boost diode can be tied
to the input (Figure 5b). The circuit in Figure 5a is more
Table 2. Capacitor Vendors
VENDOR
Panasonic
Kemet
Sanyo
Murata
AVX
Taiyo Yuden
PHONE
[phone]
[phone]
[phone]
[phone]
[phone]
URL
www.panasonic.com
www.kemet.com
www.sanyovideo.com
www.murata.com
www.avxcorp.com
www.taiyo-yuden.com
effi cient because the BOOST pin current comes from a lower
voltage source. You must also be sure that the maximum
voltage rating of the BOOST pin is not exceeded.
The minimum operating voltage of an LT3493 applica-
tion is limited by the undervoltage lockout (3.6V) and by
the maximum duty cycle as outlined above. For proper
start-up, the minimum input voltage is also limited by
the boost circuit. If the input voltage is ramped slowly,
or the LT3493 is turned on with its SHDN pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on the input and output voltages, and on the arrangement
of the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 6 shows a plot of
minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor
will present a load to the switcher which will allow it to
start. The plots show the worst-case situation where V
is ramping verly slowly. For lower start-up voltage, the
boost diode can be tied to V
input range to one-half of the absolute maximum rating
of the BOOST pin.
PART SERIES COMMENTS
Ceramic,
Polymer,
Tantalum
Ceramic,
Tantalum
Ceramic,
Polymer,
Tantalum
Ceramic
Ceramic,
Tantalum
Ceramic
EEF Series
T494, T495
POSCAP
TPS Series
IN
; however this restricts the
LT3493
11
3493fb
IN