Linear Technology LTC2920-1CS5, LTC2920-2CMS8 Quick Start Manual

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
DESCRIPTION
SINGLE AND DUAL MARGINING CONTROLLER
LTC2920-1CS5
LTC2920-2CMS8
QUICK START PROCEDURE
Referring to Figure 1, the Vcc1 and Gnd1 pins provide the power and ground connections for the LTC2920-1 (single). The Vcc2 and Gnd2 pins provide the power and ground connections for the LTC2920-2 (dual). The Vcc voltage can generally be varied between 2.2V and 6.0V. Vcc must be at least 0.6 volts higher than the voltage at the Im pin. See the LTC2920 Data Sheet for other design considerations on minimum Vcc voltage and Vcc filtering. Be sure to connect the ground pin(s) to the same ground as the power sup­ply(s) being margined.
For margining power supplies with external feedback resistors, the Im pins should be connected to the power supply feedback node. For margining power supplies using trim pins, the Im pin should be con­nected to the power supply trim pin.
The Imargin current sourced or sunk from each Im pin is individually programmed by its respective on board Rset resistor. For the LTC2920-1 circuit, there are two possible locations for the Rset resistor. Plac­ing the Rset resistor in the ‘RLOW’ position will pro­gram the Imargin current at 1V / Rset. Placing the Rset resistor in the ‘RHI’ position will program the Imargin current at 30 * 1V / Rset. See the LTC2920 Data Sheet for the specification limits of the high and low current ranges. On the LTC2920-2 circuit, there
capacitor, and pads for external connections. There are also component locations for adding 0805 resis­tors. These resistors are specific to each applica-
tion and must be installed to demonstrate Voltage Margining.
Design files for this circuit board are available. Call the LTC factory.
are two positions for each of the two Rset resistors. The ‘R1L’ and ‘R2L’ positions are similar to the ‘RLOW’ position described above. The ‘R1H’ and ‘R2H’ positions are similar to the ‘RHI’ position de­scribed above.
The In pins can be connected to a system controller that has a 3-state output, or manually connected as shown. When using a 3-state output to control the In pin, placing the (3-state) output in the high-Z state will ‘float’ the In pin, and cause the controlled Im pin to be in a high impedance state. Raising an In pin above 2.0 Volts will cause its respective Im pin to sink current. Lowering an In pin below 0.6 Volts will cause its respective Im pin to source current. See the LTC2920 Data Sheet for details. The In pins may also be controlled manually by connecting them to Vcc, ground, or left floating.
After calculating and inserting the Rset resistor(s) as described above, place the DC563 board as close as possible to the power supplie(s) being margined. The ground, Vcc, and Im pins should be connected with the shortest practical wires.
With power applied, the power supply output(s) should be at their nominal values with the In pin(s)
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
SINGLE AND DUAL MARGINING CONTROLLER
floating. Raising the In pin(s) above 2.0 V will cause the power supply output voltage to increase by the desired margin voltage. Lowering the In pin(s) below
0.6 V will cause the power supply output voltage to decrease by the desired margin voltage. When con-
nected to ‘trim’ pins on DC to DC modules, the po­larity of the voltage margining may be inverted.
If the LTC2920 Vcc pin is connected to power sup­plies that are compensated to be only ‘marginally sta­ble,’ oscillations may be observed. If oscillations are observed while margining a power supply, connect the Vcc pin to the power supply using an axial lead resistor instead of a wire. See the LTC2920 Data Sheet for calculating the value of this resistor.
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
SINGLE AND DUAL MARGINING CONTROLLER
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