Datasheet LT3439 (Analog Devices) - 4

LT3439
U U U PI FU CTIO S PGND (Pins 1, 16):
Power ground is connected to the
RT (Pin 7):
The oscillator resistor pin is used to set the emitter of the power switches via an internal sense resis- charge and discharge currents of the oscillator capacitor. tor. It has large currents flowing through it and should be The nominal value is 16.9k. The resistance can be adjusted connected to a good quality ground plane. between ±25% of nominal for better frequency accuracy.
COL A, COL B (Pins 3, 14):
These are the open collectors
SHDN (Pin 11):
The SHDN pin is used to shut down the of the output power switches. They are connected to the part. Grounding this pin will disable all internal circuitry. outer terminals of the center tap transformer. Large cur- Increasing the SHDN voltage above the turn-on threshold rents flow into these pins so external traces should be kept will enable the part. At the turn-on threshold, approxi- as short as possible. mately 20µA of current is sourced out of the pin. This current, in conjunction with the Thevenin resistance on the
RSL (Pin 4):
The slew control resistor sets the maximum pin, sets up the hysteresis. This allows the user to set the current and voltage slew rate for the collectors A and B. undervoltage lockout (UVLO) of the supply and the amount The minimum resistor value is 3.4k for fast slewing and the of start-up hysteresis with a resistor divider off of the input maximum resistor is 34k for slow slewing. For more voltage. Above 2.1V on the SHDN pin, the hysteresis details, see “Slew Rate Setting” in the Applications Infor- current is reduced to zero. If unused the pin can be left mation section of this data sheet. floating or tied directly to the input voltage.
SYNC (Pin 5):
The SYNC pin can be used to synchronize
GND (Pin 10):
Signal Ground. The oscillator, slew control the oscillator to an external clock. RT and CT should be set circuitry and the internal regulator are referred to signal such that the oscillator clock frequency is approximately ground. Internally, signal ground is tied to substrate and 10% below the external clock frequency. If unused, this the exposed backside of the device. Connect the GND pin pin should be tied to GND. For more details, see “Oscillator to the ground plane and keep the connection free of large Sync” in the Applications Information section of this data currents. sheet.
V C IN (Pin 13):
This is the supply pin for the part and should
T (Pin 6):
The oscillator capacitor pin is used in conjunc- be bypassed with a 4.7µF or greater, low ESR capacitor. tion with the RT pin to set the oscillator frequency. For When V R IN ≤ 2.5V, an internal undervoltage lockout circuit T = 16.9k, CT can be calculated as follows: will trip and turn both outputs off. CT(nF) = 70/fOSC(kHz) The transformer operating frequency and the frequency of each output is one half of the frequency of the oscillator. sn3439 3439fs 4