PLN
LED
MNT
PLN
LED
MNT
PWR
EN
GND
PWR
EN
GND
1P8V
1P5V
LED MONITOR
JMP98
JMP99
U28
JMP100
JMP101
1P5V AND 1P8V LEDS CONNECTED TO
THE VOLTAGE MONITORING CIRCUIT
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Power Monitoring LEDs
5
Power Monitoring LEDs
Each plane of the TLK6002EVM has been equipped with a voltage monitoring circuit that monitors the
voltage on the plane and lights the LEDs when the voltage is within the minimum/maximum data sheet
limits for that power supply. A precision TI voltage reference chip is used along with 0.1% precision
resistors setting minimum and maximum reference levels providing a detection circuit that is accurate to
approximately ±10 mV. The LEDs serve as a basic indication that the status of power on the board is
within the acceptable minimum/maximum limits given in the data sheet, and not as a precise
measurement tool as some LED circuits may turn off at slightly different voltages when approaching the
limits due to the manufacturing tolerances and available component values.
The voltage monitor circuits can also be bypassed, and the LEDs driven directly from the voltage on the
individual planes such as when performing voltage tolerance tests. Instead of being lit only when the
voltage on the plane is within the minimum/maximum range, the LED is lit when the voltage is greater than
the voltage needed to turn on the LED drive circuit’s NPN transistor, allowing current to flow, and the LED
to be lit from the 5-V source. In the Direct Connect mode, the base resistors have been given extra margin
to allow the LEDs to light when the voltage on the plane is a little below the minimum limit of that supply in
order to provide a LED indicator of power on the plane during voltage tolerance tests near the lower
supply limits.
Placing the jumper on the PWR side of the Voltage Monitor Enable/Disable header connects the power
plane to the input of the voltage monitoring circuit. This input is high impedance and does not load down
the power source providing the voltage to the plane.
Placing the header on the MNT side of the LED Monitor/Direct Connect selection header connects the
LED drive circuit to the output of the voltage monitor circuit causing the LED to be lit only when the
voltage is within the acceptable range.
Figure 5. TLK6002 EVM Voltage Monitor LED Enabled Example
Placing the jumper on the GND side of the Voltage Monitor Enable/Disable header disconnects the power
plane to the input of the voltage monitoring circuit and instead ties the input to GND. This prevents the
output of the voltage monitoring circuit from floating and possibly causing the LED to flicker during contact
with the board.
Placing the jumper on the MNT side of the LED Monitor/Direct Connect selection header connects the
LED drive circuit to the output of the voltage monitor circuit causing the LED to be off because the voltage
monitor circuit senses that the plane voltage is GND, which is less than the acceptable plane voltage.
9
SLLU132 – October 2010
TLK6002 Dual-Channel, 0.47-Gbps to 6.25-Gbps, Multi-Rate Transceiver
Evaluation Module
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