5 How to Make a Propagation Delay Measurement With Latch

1. Set VCCI/VCCO Power Supply to 5.0 V and disable the power supply output
2. Since the same power supply is used for both VCCI and VCCO, connect positive terminal supply to TP1 and TP2, and negative terminal to TP3
3. Ensure that cables connecting to IN+, IN-, IN+SENSE, IN-SENSE, LE/HYST, LE/HYST SENSE, OUT+, and OUT- are matched length and impedance. Perform any deskewing if necessary. If IN- is a DC voltage reference, the cables used for IN- and IN- SENSE do not need to be matched.
   1. To make accurate measurements, match all forced input voltages (IN+, IN-, LE/HYST, SHDN) and match the cables for all sensed signals (IN+SENSE, IN-SENSE, LE/HYST SENSE, SHDN SENSE).
4. On one signal generator output, set the function generator to produce a square wave output with 100mVpp at 50MHz, with a DC offset of 0.300 V. On the other generator output, set the function generator to produce a square wave output with 5.0Vpp at 5MHz, with a DC offset of 0 V and 75% duty cycle. Disable the signal generator output. Connect the first output to IN+ and the second output to LE/HYST.
5. Set one of the outputs of the DC power supply to 300mV. Disable the power supply output. Connect the output to IN-.
6. Connect OUTP and OUTN to a 50Ω terminated scope. Alternatively, use a differential probe with a 100Ω termination and connect to the oscilloscope.
7. Connect IN+SENSE, IN-SENSE, and LE/HYST SENSE, to a 50Ω terminated scope channel.
8. Enable the VCCI/VCCO power supply.
9. Verify the supply current is < 17.5mA
10. Enable the IN- power supply.
11. Enable the signal generator.
12. Monitor and verify the inputs from IN+SENSE and IN-SENSE
13. Monitor and verify the outputs for OUT+ and OUT-

Next is a scope shot capture of the inputs and outputs described in the propagation delay procedure. This is defined as the time it takes for the output to respond when latch is disabled. Here, the propagation delay between LEB/HYST (LEB denotes active low) and the differential output is measured by taking the time delta between LEB/HYST 50% rising edge (disable latch), and when OUT (differential) reaches 50% of expected value (LOW). The propagation delay after latching was measured at 2.709ns with the setup described.