Datasheet LTM8074 (Analog Devices) - 10

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PIN FUNCTIONS GND (Bank 1, A1):
Tie these GND pins to a local ground 2. Pulse-skipping mode. Float this pin for pulse-skipping plane below the LTM8074 and the circuit components. mode. This mode offers full frequency operation down In most applications, the bulk of the heat flow out of the to low output loads before pulse skipping occurs. LTM8074 is through these pads, so the printed circuit 3. Spread spectrum mode. Tie this pin high (between 2.9V design has a large impact on the thermal performance of and 4.2V) for pulse-skipping mode with spread spectrum the part. See the PCB Layout and Thermal Considerations modulation. sections for more details. 4. Synchronization mode. Drive this pin with a clock source
VIN (A3, A4):
VIN supplies current to the LTM8074’s in- to synchronize to an external frequency. During synchro- ternal regulator and to the internal power switches. These nization the part will operate in pulse-skipping mode. pins must be locally bypassed with an external, low ESR capacitor; see Table 1 for recommended values.
PG (Pin B1):
The PG pin is the open-collector output of an internal comparator. PG remains low until the FB pin volt-
VOUT (E1, E2):
Power Output Pins. Apply the output filter age is within about 10% of the final regulation voltage. The capacitor and the output load between these pins and PG signal is valid when V GND pins. IN is above 3.2V. If VIN is above 3.2V and RUN is low, PG will drive low. If this function is
RUN (Pin A2):
Pull the RUN pin below 0.9V to shut down not used, leave this pin floating. the LTM8074. Tie to 1.2V or more for normal operation. If
FB (Pin D1):
The LTM8074 regulates its FB pin to 0.774V. the shutdown feature is not used, tie this pin to the VIN pin. Connect the adjust resistor from this pin to ground.
RT (Pin B5):
The RT pin is used to program the switching The value of RFB is given by the equation RFB = 192.73/ frequency of the LTM8074 by connecting a resistor from (VOUT – 0.774), where RFB is in kΩ. this pin to ground. The Applications Information section of
TR/SS (Pin C1):
The TR/SS pin is used to provide a soft- the data sheet includes a table to determine the resistance start or tracking function. The internal 2μA pull-up current value based on the desired switching frequency. Minimize in combination with an external capacitor tied to this pin capacitance at this pin. Do not drive this pin. creates a voltage ramp. If TR/SS is less than about 0.77V,
SYNC (Pin D5):
External clock synchronization input and the FB voltage tracks to this value. The soft-start ramp time operational mode. This pin programs four different operat- is approximated by the equation t = 0.39 • C where C is ing modes: in μF. For tracking, tie a resistor divider to this pin from the 1. Burst Mode® Operation. Tie this pin to ground for Burst tracked output. This pin is pulled to ground with an internal Mode operation at low output loads—this will result in MOSFET during shutdown and fault conditions; use a series ultralow quiescent current. resistor if driving from a low impedance output. This pin may be left floating if the tracking function is not needed. Rev. 0 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Photo Package Description Typical Application Related Parts