Le87213A
Data Sheet
DEVICE OPERATIONAL NOTES
Power Supplies
The Le87213A device is implemented in a high-voltage process that allows direct powering from the –42 V to –72 V battery supply
without the need for DC to DC converters. This saves significant power that would otherwise be wasted in the DC to DC converter.
The noise on (referenced to AGND) the battery supply (VBAT pin) and on the +3.3 V supply (VCC pin) should be below the limits
as shown in Figure 1, in order not to affect the data performance.
Figure 1. Allowed Noise on Power Supply Pins (Referenced to AGND)
140
120
100
80
60
40
20
0
VBAT
VCC
0
100
200
300
400
500
600
700
800
900
1000 1100 1200
frequency kHz
Line Transformer
A step-down transformer is used to interface the Le87213A device with the TIP (A) and RING (B) line terminals. The transformer
injects the data signal onto the loop and provides dielectric isolation and impedance matching between the loop and the line driver.
The turn ratio of the transformer can be optimized to match the loop signal level to the driver output swing (see Transformer Turns
Ratio, on page 11).
Transformer Specifics
Figure 2 represents a simplified transformer model in which the boxed block is an ideal transformer with an infinite bandwidth.
Figure 2. Le87213A Transformer
TIP(A)
RPRI
RSEC
LLEAK
Secondary
Primary
ZINTR
LPRI
ZSEC
RING(B)
`
CPRI
N : 1
10
Zarlink Semiconductor Inc.
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