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| 型号： | LUCL9219GAR-DT |
| 英文描述： | Low-Cost Line Interface with Reverse Battery and Dual Current Limit |
| 中文描述： | 低成本线接口，具有反向电池和双电流限制 |
| 文件页数： | 20/30页 |
| 文件大小： | 397K |
| 代理商： | LUCL9219GAR-DT |
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Agere Systems Inc.
27
Data Sheet
November 2001
with Reverse Battery and Dual Current Limit
L9219A/G Low-Cost Line Interface
Applications (continued)
Power Derating
Operating temperature range, maximum current limit,
maximum battery voltage, minimum dc loop, and pro-
tection resistor values will influence the overall thermal
performance. This section shows the relevant design
equations and considerations in evaluating the SLIC
thermal performance.
Consider the L9219 SLIC in a 28-pin PLCC package.
The still-air thermal resistance on a 2 layer board is
43 °C/W.
The SLIC will enter the thermal shutdown state at mini-
mally 150 °C. The thermal shutdown design should
ensure that the SLIC temperature does not reach
150
°C under normal operating conditions.
Assume a maximum ambient operating temperature of
85 °C, a maximum current limit of 25 mA (including tol-
erance), and a maximum battery of –52 V. Further-
more, assume a (worst case) minimum dc loop of
200
, and that 50 protection resistors are used at
both tip and ring.
1. TTSD – TAMBIENT(max) = allowed thermal rise.
150 °C – 85 °C = 65 °C
2. Allowed thermal rise = package thermal
impedance
SLIC power dissipation.
65 °C = 43 °C/W
SLIC power dissipation
SLIC power dissipation (PDISS) = 1.51 W
Thus, if the total power dissipated in the SLIC is less
than 1.51 W, it will not enter the thermal shutdown
state. Total SLIC power is calculated as:
Total PDISS = Maximum battery
Maximum
current limit (including effects of accuracy)
+ SLIC quiescent power.
For the L9219, SLIC quiescent power (PQ) is maximum
at 0.158 W. Thus,
Total PDISS = (–52 V
[25 mA 1.05]) + 0.158 W
Total PDISS = 1.365 W + 0.158 W
Total PDISS = 1.523 W
The power dissipated in the SLIC is the total power dis-
sipation minus the power that is dissipated in the loop.
SLIC PDISS = Total power – Loop power
Loop power = (ILIM)
2
(RdcLOOP min + 2RP)
Loop power = (25 mA
1.05)2
(200
+ 100 )
Loop power = 0.207 W
SLIC power = 1.523 W – 0.207 W = 1.28
SLIC power = 1.28 W < 1.51 W
Thus, in this example, the thermal design ensures that
the SLIC will not enter the thermal shutdown state.
Pin-for-Pin Compatibility with L9217/L9218
The L9219 is an exact pin-for-pin replacement for the
L9217/18. The one minor exception is L9219 has three
logic control inputs: B0, B1, and B2. The L9218 has
only two logic control inputs, B0 and B1. Pin 13 in
L9218 is NC, so a connection between the controller
and pin 13 will not affect L9218 operation. This allows
an exact footprint match with L9219.
PCB Layout Information
Make the leads to BGND and VBAT as wide as possible
for thermal and electrical reasons. Also, maximize the
amount of PCB copper in the area of (and specifically
on) the leads connected to this device for the lowest
operating temperature.
When powering the device, ensure that no external
potential creates a voltage on any pin of the device that
exceeds the device ratings. In this application, some of
the conditions that cause such potentials during pow-
erup are the following:
1. An inductor connected to PT and PR (this can force
an overvoltage on VBAT through the protection
devices if the VBAT connection chatters).
2. Inductance in the VBAT lead (this could resonate with
the VBAT filter capacitor to cause a destructive over-
voltage).
This device is normally used on a circuit card that is
subjected to hot plug-in, meaning the card is plugged
into a biased backplane connector. In order to prevent
damage to the IC, all ground connections must be
applied before, and removed after, all other connec-
tions.
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