LT3439 LINER [Linear Technology], LT3439 Datasheet - Page 4

• Manufacturer Part Number: LT3439
• Description: Slew Rate Controlled Ultralow Noise1A Isolated DC/DC Transformer Driver
• Manufacturer: LINER [Linear Technology]

LT3439
PI FU CTIO S
PGND (Pins 1, 16): Power ground is connected to the
emitter of the power switches via an internal sense resis-
tor. It has large currents flowing through it and should be
connected to a good quality ground plane.
COL A, COL B (Pins 3, 14): These are the open collectors
of the output power switches. They are connected to the
outer terminals of the center tap transformer. Large cur-
rents flow into these pins so external traces should be kept
as short as possible.
R
current and voltage slew rate for the collectors A and B.
The minimum resistor value is 3.4k for fast slewing and the
maximum resistor is 34k for slow slewing. For more
details, see “Slew Rate Setting” in the Applications Infor-
mation section of this data sheet.
SYNC (Pin 5): The SYNC pin can be used to synchronize
the oscillator to an external clock. R
such that the oscillator clock frequency is approximately
10% below the external clock frequency. If unused, this
pin should be tied to GND. For more details, see “Oscillator
Sync” in the Applications Information section of this data
sheet.
C
tion with the R
R
The transformer operating frequency and the frequency
of each output is one half of the frequency of the oscillator.
4
T
SL
T
C
(Pin 6): The oscillator capacitor pin is used in conjunc-
U
= 16.9k, C
T
(Pin 4): The slew control resistor sets the maximum
(nF) = 70/f
U
T
can be calculated as follows:
T
OSC
pin to set the oscillator frequency. For
(kHz)
U
T
and C
T
should be set
R
charge and discharge currents of the oscillator capacitor.
The nominal value is 16.9k. The resistance can be adjusted
between 25% of nominal for better frequency accuracy.
SHDN (Pin 11): The SHDN pin is used to shut down the
part. Grounding this pin will disable all internal circuitry.
Increasing the SHDN voltage above the turn-on threshold
will enable the part. At the turn-on threshold, approxi-
mately 20 A of current is sourced out of the pin. This
current, in conjunction with the Thevenin resistance on the
pin, sets up the hysteresis. This allows the user to set the
undervoltage lockout (UVLO) of the supply and the amount
of start-up hysteresis with a resistor divider off of the input
voltage. Above 2.1V on the SHDN pin, the hysteresis
current is reduced to zero. If unused the pin can be left
floating or tied directly to the input voltage.
GND (Pin 10): Signal Ground. The oscillator, slew control
circuitry and the internal regulator are referred to signal
ground. Internally, signal ground is tied to substrate and
the exposed backside of the device. Connect the GND pin
to the ground plane and keep the connection free of large
currents.
V
be bypassed with a 4.7 F or greater, low ESR capacitor.
When V
will trip and turn both outputs off.
IN
T
(Pin 7): The oscillator resistor pin is used to set the
(Pin 13): This is the supply pin for the part and should
IN
2.5V, an internal undervoltage lockout circuit
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