Linear Technology LTC2920-1CS5 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
SINGLE AND DUAL MARGINING CONTROLLER
1
LTC2920-1CS5
LTC2920-2CMS8
DESCRIPTION
Demonstration circuit 563 contains two separate cir-
cuits: a (single channel) LTC2920-1 and a (dual chan-
nel) LTC2920-2 Power Supply Margining Controllers.
This board is meant to be connected to up to three
power supplies and demonstrates the voltage margin-
ing capabilities of the LTC2920. The board is scribed
for easy separation of the two circuits if desired.
Each circuit contains a Margining Controller, bypass
capacitor, and pads for external connections. There
are also component locations for adding 0805 resis-
tors. 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.
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 sup-
ply(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 con-
nected 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. Plac-
ing the Rset resistor in the ‘RLOW’ position will pro-
gram 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
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 de-
scribed 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)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
SINGLE AND DUAL MARGINING CONTROLLER
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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 po-
larity of the voltage margining may be inverted.
If the LTC2920 Vcc pin is connected to power sup-
plies that are compensated to be only ‘marginally sta-
ble,’ 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

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 563
SINGLE AND DUAL MARGINING CONTROLLER
3