![](http://datasheet.mmic.net.cn/90000/LT3573EMSE-TRPBF_datasheet_3495992/LT3573EMSE-TRPBF_5.png)
LT3573
3573fc
pin Functions
GND: Ground.
TEST: This pin is used for testing purposes only and must
be connected to ground for the part to operate properly.
SW: Collector Node of the Output Switch. This pin has
large currents flowing through it. Keep the traces to the
switching components as short as possible to minimize
electromagnetic radiation and voltage spikes.
VIN: Input Voltage. This pin supplies current to the internal
start-up circuitry and as a reference voltage for the DCM
comparatorandfeedbackcircuitry.Thispinmustbelocally
bypassed with a capacitor.
BIAS: Bias Voltage. This pin supplies current to the switch
driver and internal circuitry of the LT3573. This pin must
be locally bypassed with a capacitor. This pin may also be
connected to VIN if a third winding is not used and if VIN
≤ 15V. If a third winding is used, the BIAS voltage should
be lower than the input voltage for proper operation.
SHDN/UVLO:Shutdown/UndervoltageLockout.Aresistor
divider connected to VIN is tied to this pin to program the
minimum input voltage at which the LT3573 will operate.
At a voltage below ~0.7V, the part draws no quiescent
current. When below 1.25V and above ~0.7V, the part will
draw 10A of current, but internal circuitry will remain off.
Above 1.25V, the internal circuitry will start and a 10A
current will be fed into the SS pin. When this pin falls
below 1.25V, 2.5A will be pulled from the pin to provide
programmable hysteresis for UVLO.
RILIM: Maximum Current Limit Adjust Pin. A resistor
should be tied to this pin to ground to set the current
limit. Use a 10k resistor for the full current capabilities
of the switch.
SS: Soft-Start Pin. Place a soft-start capacitor here to
limit start-up inrush current and output voltage ramp
rate. Switching starts when the voltage at this pin reaches
~0.7V.
VC:CompensationPinforInternalErrorAmplifier.Connect
a series RC from this pin to ground to compensate the
switching regulator. A 100pF capacitor in parallel helps
eliminate noise.
RFB: Input Pin for External Feedback Resistor. This pin is
connected to the transformer primary (VSW). The ratio
of this resistor to the RREF resistor, times the internal
bandgap reference, determines the output voltage (plus
the effect of any non-unity transformer turns ratio). The
average current through this resistor during the flyback
period should be approximately 200A. For nonisolated
applications, this pin should be connected to VIN.
RREF: Input Pin for External Ground-Referred Reference
Resistor. This resistor should be in the range of 6k, but
for convenience, need not be precisely this value. For
nonisolated applications, a traditional resistor voltage
divider may be connected to this pin.
TC: Output Voltage Temperature Compensation. Connect
a resistor to ground to produce a current proportional to
absolute temperature to be sourced into the RREF node.
ITC = 0.55V/RTC.
Exposed Pad: Ground. The Exposed Pad of the package
providesbothelectricalcontacttogroundandgoodthermal
contact to the printed circuit board. The Exposed Pad must
should be well connected with many vias to an internal
ground plane.