JS202011SCQN datasheet(28/45 Pages) MICROCHIP

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PAC1934 Evaluation Board (ADM00805) User’s Guide

DS50002673A-page 28

 2017 Microchip Technology Inc.

nels are connected across 1Ω sense resistors R5-R8. This is called the DEMO mode

configuration. These connections are made by the first column of jumpers on the left

side of the board, J6-J13. Each jumper has a shorting shunt connected to the DEMO

side of the jumper, near the resistor string R5-R8. These resistors are all in series and

connected to the on-board current source that flows through the resistors and then

through the shunt on J5 (near the top of the board) to VDD. The shunt on J5 may be

removed to disable the on-board current source and see the noise performance of the

device with zero input. This current source generates a 0.5 Hz current square wave.

The amplitude is approximately 12.5 mA (J28 open) or 25 mA (J28 shorted, default

position). J28 is near the bottom of the board.

All of the plots in Chapter 3. “Software GUI Description” are made in DEMO mode

with the default connections.

4.3

VBUS AND VSENSE CONNECTIONS - USING EXTERNAL SOURCES FOR

SYTSTEM MODE

To use external sources for VBUS with an external load, the shunts J6 - J13 are moved

to the left (shunt position). In this configuration, connect VBUS sources to terminal 1

(top) of the screw terminal connectors J1-J4 and connect the loads to terminal 3 (bot-

tom) of these connectors. The center terminal of each connector is connected to

ground for a convenient return connection for the load. Each PAC1934 channel now

has an on-board current sense resistor of 4 mΩ connected between the positive (+)

input and negative (-) input pins, which gives 25A for the full scale current (VSENSE FSR

is fixed at 100 mV).

For options that use a different value for RSENSE than the default 1Ω, use the Settings

menu in the GUI to enter the correct sense resistor values so that ISENSE and Power

can be properly calculated (see Section 3.2 “Top Menu”).

The 4 mΩ resistors (R1-R4) can be unsoldered and replaced with a different value at

the discretion of the user. The 4 mΩ resistors have very wide metal connecting each

end to terminals 1 and 3 of the connector block, and it is challenging to remove them

cleanly. If they are removed, they will reveal a layout that facilitates soldering this wide

metal connection to each end of the new sense resistor and a kelvin connection for

each end that goes to the inputs of the PAC1934. Both the wide metal to the connector

block and the kelvin connection need to be soldered to the new sense resistor.

4.4

OTHER HARDWARE ON THE BOARD

The second columns of jumpers (J14-J17) are by default in the correct position for

either DEMO mode or System (shunt) mode. Their function is to enable measurement

of the current going into the VDD pin and the current going into the VDD_IO pin. This is

described in Section 4.7 “PAC1934 current measurements using the PAC1934.”

In the lower right corner are shorted jumpers J23 and J25 to connect the SLOW pin and

the ADDRSELECT pin to ground. Grounding the SLOW pin causes the PAC1934 to

function at the sample rate programmed by the GUI (default is 1024 samples per sec-

ond). Removing the shunt on J23 allows the SLOW pin to be pulled high, overriding the

programmed sample rate and setting the sampling rate to eight samples/second. The

ADDRSELECT pin sets the SMBus/I2C address to 20h when grounded. Removing the

shunt sets the address to 22h. Other addresses can be selected by removing the shunt

and changing the value of R22 (see the PAC1934 Data Sheet for values). Nearby is

J24 for connecting the PWRDWN to ground if desired.

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