Datasheet LTC3861-1 (Analog Devices) - 10

LTC3861-1
pin FuncTions PGOOD1 (Pin 27), PGOOD2 (Pin 14):
Power Good Indi-
VINSNS (Pin 31):
VIN Sense Pin. Connects to the VIN cator Output for Each Channel. Open-drain logic out that power supply to provide line feedforward compensation. is pulled to SGND when either channel output exceeds a A change in VIN immediately modulates the input to the ±10% regulation window, after the internal 30µs power PWM comparator and changes the pulse width in an in- bad mask timer expires. versely proportional manner, thus bypassing the feedback
I
loop and providing excellent transient line regulation. An
AVG (Pin 28):
Average Current Output Pin. A capacitor tied to ground from this pin stores a voltage proportional external lowpass filter can be added to this pin to prevent to the instantaneous average current of the master when noisy signals from affecting the loop gain. multiple outputs are paralleled together in a master-slave
TRACK/SS1 (Pin 32), TRACK/SS2 (Pin 9):
Combined configuration. Only the master phase contributes infor- Soft-Start and Tracking Inputs. For soft-start operation, mation to this average through an internal resistor when connecting a capacitor from this pin to ground will control in current sharing mode. The IAVG pin ignores channels the voltage ramp at the output of the power supply. An configured for independent operation, hence the pin internal 2.5μA current source will charge the capacitor and should be connected to SGND when the controller drives thereby control an extra input on the reference side of the independent outputs. For single output converters using error amplifier. For tracking operation, this input allows the two or more ICs, tie all of the IAVG pins together. The total start-up of a secondary output to track a primary output capacitance on the IAVG bus should range from 47pF to according to a ratio established by a resistor divider from 220pF, inclusive, with the typical value being 100pF. the primary output to the secondary error amplifier track
SGND (Pin 29, Exposed Pad Pin 33):
Signal Ground. pin. For coincident tracking of both outputs at start-up, Pins 29 and 33 are electrically connected internally. The a resistor divider with values equal to those connected exposed pad must be soldered to the PCB ground for to the secondary VSNSP pin from the secondary output rated thermal performance. All soft-start, small-signal should be used to connect the secondary track input and compensation components should return to SGND. from the primary output. This pin is internally clamped to 1.2V, and is used to communicate over current events
CONFIG (Pin 30):
Line Feedforward Configuration Pin. in a master-slave configuration. This pin allows the user to configure the multiplier to achieve accurate modulator gain over varying VIN and switching frequencies. This pin can be connected to VCC or SGND. An internal resistor will pull this pin to SGND when it is floated. 38611fb 10 For more information www.linear.com/LTC3861-1 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Typical Applications Package Description Related Parts