SC173MLTRT Semtech, SC173MLTRT Datasheet - Page 19

• Manufacturer Part Number: SC173MLTRT
• Description: IC BUCK SYNC ADJ 3A MLPD-10
• Manufacturer: Semtech
• Series: EcoSpeed™r
• Type: Step-Down (Buck)r

Specifications of SC173MLTRT

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.75 ~ 5.23 V
• Current - Output: 3A
• Frequency - Switching: 200kHz ~ 1MHz
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MLPD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: SC173MLTR

Applications Information (continued)
The use of 1% feedback resistors may result in up to an
additional 1% error. If tighter DC accuracy is required, re-
sistors with lower tolerances should be used.
The output inductor value may change with current. This
will change the output ripple and therefore will have a
minor effect on the DC output voltage. The output ESR
also affects the output ripple and thus has a minor effect
on the DC output voltage.
Switching Frequency Variation
The switching frequency will vary depending on line and
load conditions. The line variations are a result of fixed
propagation delays in the on-time one-shot, as well as
unavoidable delays in the power FET switching. As V
increases, these factors make the actual DH on-time
slightly longer than the ideal on-time. The net effect is
that frequency tends to fall slightly with increasing input
voltage.
The switching frequency also varies with load current
as a result of the power losses in the MOSFETs and the
inductor. For a conventional PWM constant-frequency
converter, as load increases the duty cycle also increases
slightly to compensate for IR and switching losses in the
MOSFETs and inductor. A adaptive on-time converter
must also compensate for the same losses by increasing
the effective duty cycle (more time is spent drawing en-
ergy from V
ly constant for a given V
the losses the off-time will tend to reduce slightly as load
increases. The net effect is that switching frequency in-
creases slightly with increasing load.
Switching Node Voltage Spike
Due to parasitic board inductance, the transient LX pin
voltage at the point of measurement may appear larger
than that which exists on silicon. With an input multilay-
er ceramic capacitor of 10uF placed less than 3mm away
from the PVIN pin, the device is designed and guaranteed
to tolerate the short transient voltages, of maximum
20ns duration, that will appear on the LX pin due to the
© 2010 Semtech Corporation
IN
as losses increase). The on-time is essential-
OUT
and V
IN
combination, to offset
IN
deadtime diode conduction, as long as the transient volt-
age on PVIN is less than 6.0V. The time duration of the
transient LX pin voltage is measured on the voltage por-
tion which is either over 6.0V for positive voltage spike
or under -1V for negative voltage spike. The LX voltage
is measured from the LX pin to the PGND pin by using a
probing loop which is as short as possible to minimize or
eliminate the switching noise pick up.
SC173
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