LTM8027MPVPBF datasheet(9/20 Pages) LINER

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LTM8027

8027f

PIN FUNCTIONS

VIN (Bank 3): The VIN pin supplies current to the LTM8027’s

internal regulator and to the internal power switch. This

pin must be locally bypassed with an external, low ESR

capacitor (see Table 2).

VOUT (Bank 1): Power Output Pins. Apply the output ﬁlter

capacitor and the output load between these and the GND

pins.

AUX (Pin A7): Low Current Voltage Source for BIAS1and

BIAS2. In many designs, the BIAS pins are simply connected

to VOUT. The AUX pin is internally connected to VOUT and

is placed near the BIAS pins to ease printed circuit board

routing. Although this pin is internally connected to VOUT,

do NOT connect this pin to the load. If this pin is not tied

to BIAS1 and BIAS2, leave it ﬂoating.

BIAS1 (Pin A6): The BIAS1 pin connects to the internal

power bus. Connect to a power source greater than 8.5V.

If the output is greater than 8.5V, connect it to this pin. If

the output voltage is less, connect this to a voltage source

between 8.5V and 15V. For proper operation, connect this

pin to the same power source as BIAS2.

BIAS2 (Pin A3): Internal Biasing Power. This pin must be

connected to the same power source as BIAS1 for proper

operation. Always connect this pin to a voltage source

above 8.5V. Do not leave BIAS2 ﬂoating.

RUN (Pin A4): Tie the RUN pin to ground to shut down the

LTM8027. Tie to 1.4V or more for normal operation. The

RUN pin is internally clamped to 5V, so when it is pulled

up, be sure to use a pull-up resistor that limits the cur-

rent in to the RUN pin to less than 1mA. If the shutdown

feature is not used, tie this pin to the VIN pin through a

pull-up resistor.

GND (Bank 2): Tie these GND pins to a local ground plane

below the LTM8027 and the circuit components.

RT (Pin B1): The RT pin is used to program the switching

frequency of the LTM8027 by connecting a resistor from

this pin to ground. The Applications Information section of

the data sheet includes a table to determine the resistance

value based on the desired switching frequency. Minimize

capacitance at this pin.

SYNC (Pin C1): The SYNC pin provides an external clock

input for synchronization of the internal oscillator. The

RT resistor should be set such that the internal oscilla-

tor frequency is 10% to 25% below the external clock

frequency. If unused, the SYNC pin is connected to GND.

For more information see Oscillator Sync in the Application

Information section of this data sheet.

ADJ (Pin A2): The LTM8027 regulates its ADJ pin to 1.23V.

Connect the adjust resistor from this pin to ground. The

value of RADJ is given by the equation:

RADJ = 613.77/(VOUT – 1.23)

where RADJ is in kΩ.

SS (Pin A5): The soft-start pin is used to program the

supply soft-start function. Use the following formula to

calculate CSS for a given output voltage slew rate:

CSS = 2μA(tSS/1.231V)

The pin should be left unconnected when not using the

soft-start function.

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