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Circuit Use and Modifications

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4 Circuit Use and Modifications

Besides the required circuitry to operate the TPS62366A (outlined in a white silk screen border on the

PCB), there are additional circuits present on the TPS62366AEVM-757 that assist in evaluating the

TPS62366A as a processor power supply solution. Additionally, there are modifications that can be made

to adapt the circuit's performance to the needs of a particular application.

4.1 Load Step Circuit

The TPS62366AEVM-757 contains a simple circuit that produces fast load current steps at the output of

the TPS62366A. This evaluates the response of the TPS62366A to various load transients. To operate

this circuit, connect a function generator to TP4. The output of the function generator should be a square

wave with a small duty cycle. The output high level controls the gate to source voltage of the power

transistor, Q1, and should be adjusted to generate the desired step current high level. The output low level

sets the step current low level. Good settings to start with are a square wave signal running at 100 Hz and

5% duty cycle going from 0V to 3V. These settings can be adjusted in order to generate the desired load

step.

Resistor R6 is present to observe the load step current by measuring the voltage across TP2 and TP3.

Oscilloscope settings of 100mV / div translate to a current in R6 of 1A / div.

4.2 Output Voltage Buffer

The output voltage buffer circuit simply buffers the SNS+/- output with a unity gain op amp. This

transforms SNS+ and SNS- to a lower impedance signal that can be measured by high impedance

measurement equipment, such as an oscilloscope. The op amp, U2, is powered from the USB-TO-GPIO

adaptor. The USB-TO-GPIO adaptor must be installed for the output voltage buffer circuit to operate.

C14 is provided to reduce the bandwidth and noise of the input signal to the operational amplifier.

4.3 Circuit Modifications

Modifications may be made to the circuit. Any modifications affect the performance of the EVM and must

remain within the limits of the TPS62366A IC, as detailed in the datasheet.

4.3.1 Output Capacitors

There are four locations for extra output capacitors to be installed in order to reduce output ripple or

lessen the voltage drop due to a load transient. C7 allows an extra capacitor to be installed near the

TPS62366A IC, while C10, C11, and C12 allow extra capacitors to be installed closer to the point of load,

which is simulated by the load step circuit. The total output capacitance must remain below the maximum

capacitance allowed in the datasheet. C10, C11, and C12 come pre-installed with typical capacitances

used at the processor's input.

4.3.2 Input Capacitors

C9 is provided to locate additional input capacitance near the TPS62366A input. Additional capacitance at

C9 decreases the input voltage ripple.

C8 is provided to form a complete 'PI'-type filter for the AVIN input. With the change of R1 to some small

value (around 10 Ω), the C-R-C filter is complete. This filter is not necessary for operation of the

TPS62366A.

4.3.3 I

C Pull-up Resistors

R2 and R3 are locations for optional pull-up resistors for the I

C signals. They are required when not using

the USB-TO-GPIO adaptor but are not recommended when using the adaptor. If used, their typical value

is around 2.2kΩ.

TPS62366AEVM-757 SLVU690–April 2012

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