Datasheet

GSL

Drain Current

12V

Normal

Operation

Constant

Power

LIM

, 5.5A

Turn-on

Source VoltageGate-to-

Board Layout and Probing Cautions

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Figure 3. Power Up Using Power Limit and Current Limit

4 Board Layout and Probing Cautions

The Figure 1 shows the placement of the circuit components. The following should be kept in mind when

the board is powered:

1. High voltage, equal to VIN, is present on C3, C4, C7, Q1, and various points within the circuit. Use

CAUTION when probing the circuit to prevent injury, as well as possible damage to the circuit.

2. At maximum load current (5.5A), the wire size and length used to connect the power source and the

load become important. The wires connecting this evaluation board to the power source SHOULD BE

TWISTED TOGETHER to minimize inductance in those leads. The same applies for the wires

connecting this board to the load. This recommendation is made in order to minimize high voltage

transients from occurring when the load current is shut off.

5 Board Connections/Startup

The input voltage source is connected to the J1 connector, and the load is connected to the J2 connector

at the OUT and GND terminals. USE TWISTED WIRES. A voltmeter should be connected to the input

terminals, and one to the output terminals. The input current can be monitored with an ammeter or current

probe. To monitor the status of the PGD output, connect a voltmeter from PGOOD to GND on the J2

terminal block. Put the toggle switch in the ON position.

Increase the input voltage gradually. The input current should remain less than 2 mA until the upper UVLO

threshold is reached (≊34.4V). When the threshold is reached, Q1 is turned on as described in Section 3.

If viewed on an oscilloscope, the input current increases as shown in Figure 3 before settling at the value

defined by the load. The turn-on timing depends on the input voltage, power limit setting, current limit

setting, and the final load current, and is between ≊3.0 ms with no load current, and ≊7.5 ms with a 4A

load current, with VIN = 36V. See Figure 3, Figure 9, and Figure 10.

6 Circuit Parameter Changes

Current Limit

The current limit threshold is set by R10 according to the following equation:

LIM

= 55 mV/R10 (1)

If the load current increases such that the voltage across R10 reaches 55 mV, the LM5069 then

modulates Q1’s gate to limit the current to that level. This evaluation board is supplied with a 10 mohm

resistor for R10, resulting in a current limit of 5.5A. To change the current limit threshold replace R10 with

a resistor of the required value and power capability.

AN-1522 LM5069 Evaluation Board SNVA184B–September 2006–Revised May 2013

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