TDE1890 ST Microelectronics, TDE1890 Datasheet - Page 7

• Manufacturer Part Number: TDE1890
• Description: 2A HIGH-SIDE DRIVER INDUSTRIAL INTELLIGENT POWER SWITCH
• Manufacturer: ST Microelectronics

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 package and ambient temperature.
At ambient temperature close to upper limit
(+85 C) and in the worst operating conditions, it is
possible that the chip temperature could 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
2)
a) power lost in the switch:
b) power due to quiescent current in the ON
c) an external LED could be used to visualize
NDMOS (the real switch) of the device in-
creases with its temperature.
Experimental results show that silicon resistiv-
ity increases with temperature at a constant
rate, rising of 60% from 25 C to 125 C.
The relationship between R
perature is therefore:
device is due to three contributes:
where:
Thus the total ON state power consumption is
given by:
In the right side of equation 1, the second and
In the ON state the power dissipated in the
P
rent);
state Iq, sunk by the device in addition to
I
the switch state (OUTPUT STATUS pin).
Such a LED is driven by an internal current
source (delivering I
the voltage drop across the LED, the dissi-
pated power is: P
out
T
R
k is the constant rate (k
(see fig. 4).
P
j
out
DSON0
: P
R
is the silicon temperature in C
on
DSON
q
I
out
P
is R
I
out
q
2
R
DSON
R
V
DSON0
P
s
DSON
(V
q
os
at T
os
s
) and therefore, if V
P
is the supply voltage);
(I
j
=25 C
I
1
out
os
DSON
os
is the output cur-
4.711
k
V
DSON
of the output
T
s
j
10
V
25
and tem-
(1)
os
3
)
.
os
is
3) The chip temperature must not exceed
Referring to application circuit in fig. 6, let us con-
sider the worst case:
- The supply voltage is at maximum value of in-
in order do not lose the control of the device.
The heat dissipation path is represented by
the thermal resistance of the system device-
ambient (R
parameter relates the power dissipated P
the silicon temperature T
temperature T
dustrial bus (30V instead of the 24V nominal
value). This means also that I
(2.5A instead of 2A).
the third element are constant, while the first
one increases with temperature because
R
From this relationship, the maximum power
P
ing
T
Replacing the expression (1) in this equation
and solving for I
current versus ambient temperature relation-
ship:
where R
course, I
maximum operative current I
From the expression (2) we can also find the
maximum ambient temperature T
a given power P
In particular, this relation is useful to find the
maximum ambient temperature T
which I
T
amb
on
DSON
I
T
Lim
outx
ambx
j
which can be dissipated without exceed-
P
is:
Lim at a given ambient temperature
q
T
outx
increases as well.
T
amb
amb
outx
DSON
I
P
can be delivered:
out
th
P
Lim
os
). In steady state conditions, this
on
amb
2
values are top limited by the
x is R
P
out
Lim
on
R
on
Lim P
R
:
, we can find the maximum
can be dissipated:
DSONx
I
th
Lim T
R
outx
R
th
TDE1890 - TDE1891
R
T
DSON
th
R
2
amb
th
on
DSONx
j
R
P
amb
and the ambient
outx
R th
DSONx
at T
q
outx
P
q
(2A nominal).
P
rises of 25%
amb
j
= Lim. Of
os
P
(4)
(2)
at which
ambx
os
R
on
th
Lim
7/12
to
at