ltm8027 Linear Technology Corporation, ltm8027 Datasheet - Page 9

• Manufacturer Part Number: ltm8027
• Description: 60v, 4a Dc/dc ?module Regulator
• Manufacturer: Linear Technology Corporation

PIN FUNCTIONS
V
internal regulator and to the internal power switch. This
pin must be locally bypassed with an external, low ESR
capacitor (see Table 2).
V
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 V
is placed near the BIAS pins to ease printed circuit board
routing. Although this pin is internally connected to V
do NOT connect this pin to the load. If this pin is not tied
to BIAS1 and BIAS2, leave it fl oating.
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 fl oating.
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 V
pull-up resistor.
IN
OUT
(Bank 3): The V
OUT
(Bank 1): Power Output Pins. Apply the output fi lter
. The AUX pin is internally connected to V
IN
pin supplies current to the LTM8027’s
IN
pin through a
OUT
OUT
and
,
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
R
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 R
where R
SS (Pin A5): The soft-start pin is used to program the
supply soft-start function. Use the following formula to
calculate C
The pin should be left unconnected when not using the
soft-start function.
T
R
C
resistor should be set such that the internal oscilla-
SS
ADJ
= 2μA(t
= 613.77/(V
ADJ
ADJ
SS
is in kΩ.
for a given output voltage slew rate:
is given by the equation:
SS
/1.231V)
OUT
– 1.23)
LTM8027
9
8027f