參數(shù)資料
型號(hào)： TDE1898RDP
廠商： 意法半導(dǎo)體
英文描述： 0.5A HIGH-SIDE DRIVER INDUSTRIAL INTELLIGENT POWER SWITCH
中文描述： 0.5A的高邊驅(qū)動(dòng)器工業(yè)智能功率開(kāi)關(guān)
文件頁(yè)數(shù)： 6/12頁(yè)
文件大小： 121K
代理商： TDE1898RDP
WORST CONDITION POWER DISSIPATION IN
THE ON-STATE
In IPS applications the maximum average power
dissipation occurs when the device stays for a
long time in the ON state. In such a situation the
internal temperature depends on delivered cur-
rent (and related power), thermal characteristics
of the packageand ambient temperature.
At ambient temperature close to upper limit
(+85
°
C) and in the worst operating conditions,it is
possible that the chip temperaturecould increase
so much to make the thermal shutdown proce-
dure untimely intervene.
Our aim is to find the maximum current the IPS
can withstand in the ON state without thermal
shutdown intervention, related to ambient tem-
perature. To this end, we should consider the fol-
lowing points:
1) The ON resistance R
DSON
of the output
NDMOS (the real switch) of the device in-
creases with its temperature.
Experimentalresults showthat silicon resistiv-
ity increases with temperature at a constant
rate, risingof 60% from 25
°
C to 125
°
C.
The relationship between R
DSON
and tem-
peratureis therefore:
R
DSON
=
R
DSON0
(
1
+
k
)
(
T
j
±
25
)
where:
T
j
is the silicon temperature in
°
C
R
DSON0
is R
DSON
at T
j
=25
°
C
k is theconstant rate (k
=
4.711
10
±
3
)
(see fig.4).
2)
In the ON state the power dissipated in the
device is dueto three contributes:
a) power lost in the switch:
P
out
=
I
out2
R
DSON
(I
out
is theoutput cur-
rent);
b) power due to quiescent current in the ON
state Iq,sunk by the device in additionto
I
out
: P
q
=
I
q
V
s
(V
s
is the supplyvoltage);
c) an external LED could be used to visualize
the switchstate (OUTPUT STATUS pin).
Such a LEDis driven by aninternal current
source (delivering I
os
) and therefore,if V
os
is
the voltagedrop across the LED, the dissi-
pated power is: P
os
=
I
os
(
V
s
±
V
os
)
.
Thus the total ON statepower consumptionis
given by:
P
on
=
P
out
+
P
q
+
P
os
(1)
In the right side of equation 1, the secondand
the third element are constant, while the first
one increases with temperature because
R
DSON
increasesas well.
3) The chip temperature must not exceed
Θ
Lim
in orderdo not lose the control of the device.
The heat dissipation path is represented by
the thermal resistance of the system device-
board-ambient (R
th
). In steady state condi-
tions, this parameter relates the power dissi-
pated P
on
to the silicon temperature T
j
and
the ambienttemperatureT
amb
:
T
j
±
T
amb
=
P
on
R
th
(2)
From this relationship,the maximum power P
on
which can be dissipated without exceeding
Θ
Lim at a given ambient temperature T
amb
is:
P
on
=Θ
Lim
±
T
amb
R
th
Replacing the expression (1) in this equation
and solving for I
out
, we can find the maximum
current versus ambient temperature relation-
ship:
I
outx
=
√
Θ
Lim
±
T
amb
R
th
±
P
q
±
P
os
where R
DSON
x is R
DSON
at T
j
=
Θ
Lim. Of
course, I
outx
values are top limited by the
maximum operative current I
outx
(500mA
nominal).
From the expression (2) we can also find the
maximum ambient temperature T
amb
at which
a given power P
on
can be dissipated:
T
amb
= Θ
Lim
±
P
on
R th
=
= Θ
Lim
±
(
I
out
2
R
DSONx
+
P
q
+
P
os
)
R
th
In particular, this relation is useful to find the
maximum
ambient temperature T
ambx
which I
outx
can be delivered:
at
T
ambx
= Θ
Lim
± (
I
outx2
R
DSONx
+
+
P
q
+
P
os
)
R
th
(4)
Referring to application circuit in fig. 5, let us con-
sider the worstcase:
- The supply voltage is at maximumvalue of in-
dustrial bus (30V instead of the 24V nominal
value). This means also that I
outx
risesof 25%
TDE1897R - TDE1898R
6/12
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