Microchip Technology MCP1726, User Manual

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MCP1726 Evaluation Board User’s Guide
DS51550A-page 8
©
2005 Microchip Technology Inc.
2.4 TESTING CIRCUIT 1 OF THE MCP1726 1A LDO EVALUATION BOARD
2.4.1 Power Input and Output Connections
Powering the MCP1726 1A LDO Evaluation Board
Apply the input voltage to test points TP7 (VIN1) and TP8 (GND). Connect the positive
side of the input source (+) to test point TP7 (VIN1). Connect the negative, or return,
side (–) of the input source to the test point TP8 (GND). These two test points are
located on the upper left side of the board. The power supply input voltage must be in
the specified operating range for the board to operate correctly. The UVLO feature of
the MCP1726 prevents the device from operating when the input voltage is too low (see
data sheet for UVLO thresholds).
When input voltage is applied and is above the input UVLO threshold, the LDO output
will turn on automatically. The SHDN1 input has been pulled up to VIN1 which turns the
device on. The LDO output can be turned off by pulling the SHDN1 input (TP9) low
(short SHDN1 to GND).
When input voltage is applied, the red portion of the D2 LED will illuminate. As long as
input voltage is present, the red portion of this LED will be on.
Applying the load to the MCP1726 1A LDO Evaluation Board
To apply a load to VOUT1 of the MCP1726 1A LDO Evaluation Board, the positive-side
of the load (+) should be connected to test point TP12 (VOUT1). The negative side of
the load (–) should be connected to test point TP10 (GND).
The maximum output current of the MCP1726 is 1.0A. If the output load exceeds this
level, the MCP1726 will go into current limit at 1.7A. If, during the overload condition,
the device junction temperature exceeds the overtemperature limit of 150°C, the output
of the LDO will turn off and wait for the junction temperature to cool down before turning
the LDO output back on. Circuit 1 of the MCP1726 1A LDO Evaluation Board evaluates
the 3X3 DFN package. When operating at room ambient, this circuit will go into
overtemperature shutdown when the power dissipation in the device reaches about
2.1W.
2.4.2 Adjusting the Output Voltage of the LDO
The MCP1726 1A LDO Evaluation Board comes with the output voltage preset to 2.5V.
To adjust the output voltage (VOUT1) of circuit 1, the potentiometer, R10, is used. R10
is a top-side adjust potentiometer. If the desired output voltage is higher than 2.5V,
raise the input voltage to a level that is higher than your desired output voltage. Use a
small flathead screwdriver to adjust the R10 potentiometer and monitor the VOUT1
(TP12) voltage. If your desired output voltage is less than 2.5V, the input voltage of the
LDO must be set to a minimum of 2.3V, as this is the minimum input voltage of the LDO.
The output voltage of the LDO can then be adjusted using the R10 potentiometer.
The potentiometer will allow you to adjust the output voltage over the full range of 0.8V
to 5.0V. If you would like to use fixed resistor values to set the output voltage of the
LDO, the potentiometer can be removed and the pads for the potentiometer can be
used to solder your fixed value resistors into the circuit.