參數(shù)資料
型號: LUCL9217GAR-D
英文描述: Aluminum Snap-In Capacitor; Capacitance: 10000uF; Voltage: 25V; Case Size: 25x30 mm; Packaging: Bulk
中文描述: 低成本線接口,具有反向電池和PPM
文件頁數(shù): 28/30頁
文件大小: 414K
代理商: LUCL9217GAR-D
28
Agere Systems Inc.
Data Sheet
November 2001
with Reverse Battery and PPM
L9217A/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 L9217 SLIC in a 28-pin PLCC package.
The thermal resistance on a 2-layer board with natural
convection is 43 °C/W.
The SLIC will enter the thermal shutdown state at a
minimum of 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 design current limit of 25 mA, and a maximum
battery of –52 V. Furthermore, assume a (worst-case)
minimum dc loop of 200
, and that 50
protection
resistors are used at both tip and ring.
1. T
TSD
– T
AMBIENT(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 (P
DISS
) = 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 P
DISS
= Maximum battery
maximum
current limit (including effects of accuracy)
+ SLIC quiescent power
For the L9217, SLIC quiescent power (P
Q
) is maximum
at 0.175 W. Thus,
Total P
DISS
= (–52 V
[25 mA
1.08])
+ 0.175 W
Total P
DISS
= 1.404 W + 0.175 W
Total P
DISS
= 1.579 W
The power dissipated in the SLIC is the total power dis-
sipation minus the power that is dissipated in the loop.
SLIC P
DISS
= Total power – loop power
Loop power = (I
LIM
)
2
(R
dcLOOP
min + 2R
P
)
Loop power = (25 mA
1.08)
2
(200
+ 100
)
Loop power = 0.219 W
SLIC power = 1.579 W – 0.219 W = 1.36
SLIC power = 1.36 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 L9218/L9219
The L9217 can be a pin-for-pin replacement for the
L9218/L9219. The exceptions are as follows: L9217
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 con-
troller and pin 13 will not affect L9218 operation. In
L9217, pin 28 is PPMOUT, pin 21 is PPMIN, and pin 27
is OVH. In L9218/9, pin 28 is NC, pin 21 is NC, and pin
27 is TSD
PCB
Layout Information
Make the leads to BGND and V
BAT
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, make certain that no exter-
nal 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 dur-
ing powerup are the following:
1. An inductor connected to PT and PR (this can force
an overvoltage on V
BAT
through the protection
devices if the V
BAT
connection chatters).
2. Inductance in the V
BAT
lead (this could resonate
with the V
BAT
filter capacitor to cause a destructive
overvoltage).
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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