APPLICATION NOTE 402

Additional Pulse Amplitude Settings for DS2148, DS21348, DS21Q48, DS21Q348 and DS21448


Abstract: This application note shows how to use undocumented settings to modify output amplitudes.

Introduction

This application note provides the register settings for the DS2148/DS21348/DS21Q48/DS213Q48 and DS21448 to configure the transmitter for pulse amplitudes that are different than the line build-out (LBO) modes documented in the respective data sheets. The following tables list the register settings and define the resulting pulse amplitudes for the 3.3V (DS21348, DS21Q348) and 5V (DS2148, DS21Q48) devices.

Table 1. DS21348, DS21Q348 Register Settings
Operating Voltage: 3.3V (VSM pin wired low)
Applicable Devices: DS21348, DS21Q348
Applicable Device Revisions: A2, B1, C1, and C2 (DS21Q348)
Operating Mode: E1
L2
(CCR4.7)
L1
(CCR4.6)
L0
(CCR4.5)
APPLICATION TYPICAL CHANGE IN
PULSE AMPLITUDE
RETURN
LOSS (dB)
Rt (Ω)
0 1 0 75Ω normal 7% enhancement over LBO setting 0 N.M. 0
0 1 1 120Ω normal 8% enhancement over LBO setting 1 N.M. 0
1 1 0 120Ω normal with high return loss 8% attenuation over LBO setting 5 21 9.1
1 1 1 120Ω normal with high return loss 4% attenuation over LBO setting 5 21 10
N.M. = not meaningful

Table 2. DS2148, DS21Q48 Register Settings
Operating Voltage: 5V (VSM pin wired high)
Applicable Devices: DS2148, DS21Q48
Applicable Device Revisions: A2, B1, C1 and C2 (DS21Q48)
Operating Mode: E1
L2
(CCR4.7)
L1
(CCR4.6)
L0
(CCR4.5)
APPLICATION TYPICAL CHANGE IN
PULSE AMPLITUDE
RETURN
LOSS (dB)
Rt (Ω)
0 1 0 75Ω normal 10% enhancement over LBO setting 0 N.M. 0
0 1 1 120Ω normal 10% enhancement over LBO setting 1 N.M. 0
1 1 0 120Ω normal with high return loss 10% attenuation over LBO setting 5 21 22
1 1 1 120Ω normal with high return loss 10% enhancement over LBO setting 5 21 33

In addition to the these settings, additional pulse amplitudes can be obtained in the following devices by setting test register 2 (Address 14h) as per Table 3.

Table 3. Additional Pulse Amplitude Settings
OPERATING MODE APPLICABLE DEVICES APPLICABLE DEVICE REVISIONS TEST2 (ADDRESS 14h) REGISTER SETTINGS TYPICAL CHANGE IN
PULSE AMPLITUDE
E1 DS21348, DS21Q348 C1 D0 38% enhancement over LBO setting 0, 1, 2, and 3
DS21348, DS21Q348, DS2148, DS21Q48 C1 E0 19% enhancement over LBO setting 0, 1, 2, and 3
T1/J1 DS21348, DS21Q348 C1 D0 38% enhancement over LBO setting 0, 5, 6, and 7
DS21348, DS21Q348, DS2148, DS21Q48 C1 E0 19% enhancement over LBO setting 0, 5, 6, and 7
E1
DS21448 A1 D0 33% enhancement over LBO setting 0, 1, 2, and 3
T1/J1
DS21448 A1 D0 33% enhancement over LBO setting 0, 5, 6, and 7

In addition to the above settings, writing a HEX BO in address 14h (register TEST2) reduces any tendency of the waveform to ring.

To learn more about testing Dallas Semiconductor line interface units and transceivers for compliance to T1/J1 and E1 pulse mask specifications, refer to Application Note 397: Pulse Template Measurement
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APP 402:
APPLICATION NOTE 402,AN402, AN 402, APP402, Appnote402, Appnote 402