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Power Supply Configuration

4 Power Supply Configuration

Two power supplies are needed to bias the SN65LVDS4 – VCC, the core power supply, and VDD, the

output drive power supply. For proper device operation, it is recommended that VCC is powered up first

and then VDD or VCC applied at the same time as VDD (In the later case, VCC and VDD are tied

together). Further, it is also recommended that VCC is equal to or less than VDD as shown in Table 1.

Table 1. Power Supply Acceptable Combinations

VCC (V) VDD (V) Recommended

1.8 1.8 Yes

1.8 2.5 Yes

1.8 3.3 Yes

2.5 1.8 No

2.5 2.5 Yes

2.5 3.3 Yes

5 Test Setup

Measuring the output signal on J2 with a 50-Ω cable terminated into 50 Ω at the scope attenuates the

signal due to the 453-Ω resistor (R1) in series with the receiver output on the EVM board. The resistor is

installed as a current limit for termination into a 50-Ω load, thus providing a 10x attenuation on the

measured output signal.

Measuring the output signal with a high-impedance probe on JMP1 requires removing R1, the 453-Ω

resistor, and installing a 0-Ω resistor on R4 (0402). Measuring the output signal on JMP1 allows the user

to see absolute signal levels out of the device.

See Table 2 for input and output connections.

Table 2. EVM and Device Connections

EVM Connection I/O Description

Name No.

J1 A 2 I LVDS input, positive

J3 B 3 I LVDS input, negative

P2 GND 1, 7 — Ground

— NC 4, 6, 9 — No connect

J2 R 8 O 1.8/2.5 LVCMOS/3.3 LVTTL output

P1 VCC 5 — Core supply voltage

P3 VDD 10 — Output supply voltage

SLLU151– July 2011 SN65LVDS4 Evaluation Module

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