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參數(shù)資料
| 型號(hào)： | MC33091A |
| 廠商： | Motorola, Inc. |
| 英文描述： | HIGH-SIDE TMOS DRIVER |
| 中文描述： | 高邊的TMOS驅(qū)動(dòng) |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 267K |
| 代理商： | MC33091A |
MC33091A
APPLICATION
12
MOTOROLA ANALOG IC DEVICE DATA
The following design approach will simplify application of
the MC33091A and will insure the components chosen to be
optimal for a specific application.
1. Characterize the load impedance and determine
the maximum load current possible for the load supply
voltage used.
2. Select a TMOS device capable of handling the
maximum load current. Though the MC33091A will equally
drive our competitors products, it is hoped you will select one
of the many TMOS devices listed in Motorola’s Power
MOSFET Transistor Data Book
3. Determine the maximum steady state VDS voltage the
TMOS device will experience under normaloperating
conditions. Typically, this is the maximum load current
multiplied by the specified RDS(on) of the TMOS device.
Junction temperature considerations should be taken into
account for the RDS(on) value since it is significantly
temperature dependent. Normally, TMOS data sheets depict
the effect of junction temperature on RDS(on) and an RDS(on)
value at some considered maximum junction temperature
should be used. Various graphs relating to RDS(on) are
depicted in Motorola TMOS data sheets. Though Motorola
TMOS devices typically specify a maximum allowable
junction temperature of 150
°
C, in a practical sense, the user
should strive to keep junction temperature as low as possible
so as to enhance the applications long term reliability. The
maximum steady state VDS voltage the TMOS device will
experience under normaloperating conditions is thus:
VDS(norm) = IL(max)RDS(on)
(14)
4. Calculate the maximum power dissipation of the TMOS
device under normaloperating conditions:
PD(max) = VDS(on)IL(max)
(15)
5. The calculated maximum power dissipation of the
TMOS device dictates the required thermal impedance for
the application. Knowing this, the selection of an appropriate
heatsink to maintain the junction temperature below the
maximum specified by the TMOS manufacture for operation
can be made. The required overall thermal impedance is:
TRJA = (TJ(max) – TA(max))/PD(max)
(16)
Where TJ(max), the maximum allowable junction
temperature, is found on the TMOS data sheet and TA(max),
the maximum ambient temperature, is dictated by the
application itself.
6. The thermal resistance, TRJA, represents the maximum
overall or total thermal resistance, from junction to the
surrounding ambient, allowable to insure the TMOS
manufactures maximum junction temperature will not be
exceeded. In general, this overall thermal resistance can be
considered as being made up of several separate minor
thermal resistance interfaces comprised of TRJC, TRCS and
TRSA such that:
TRJA = TRJC + TRCS + TRSA
(17)
Where TRJC, TRCS and TRSA represent the junction–to–
case, case–to–heatsink and heatsink–to–ambient thermal
resistances respectively. TRCS and TRSA are the only
parameters the device user can influence.
The case–to–heatsink thermal resistance, TRCS, is
material dependent and can be expressed as:
TRCS =
ρ
Where “
ρ
” is the thermal resistivity of the heatsink material
(expressed in
°
C/Watt/Unit Thickness), “t” is the thickness of
heatsink material, and “A” is the contact area of the
case–to–heatsink. Heatsink manufactures specify the value
of TRCS for standard heatsinks. For nonstandard heatsinks,
the user is required to calculate TRCS using some form of the
basic Equation 18.
The required heatsink–to–ambient thermal resistance,
TRSA, can easily be calculated once the terms of Equation 17
are known. Substituting TRJA of Equation 16 into Equation 17
and solving for TRSA produces:
TRSA = (TJ(max)–TA(max))/PD(max)–(TRJC+TRCS) (19)
t/A
(18)
Consulting the heatsink manufactures catalog will provide
TRCS information for various heatsinks under various
mounting conditions so as to allow easy calculation of TRSA
in units of
°
C/W (or when multiplied by the power dissipation
produces the heatsink mounting surface temperature rise).
Furthermore, heatsink manufactures typically specify for
various heatsinks, heatsink efficiency in the form of mounting
surface temperature rise above the ambient conditions for
various power dissipation levels. The user should insure that
the heatsink selected will provide a surface temperature rise
somewhat less than the maximum capability of the heatsink
so that the device junction temperature will not be exceeded.
The user should consult the heatsink manufacturers catalog
for this information.
7. Set the value of VDS(min) to something greater than the
normal operatingdrain to source voltage, VDS(norm), the
TMOS device will experience as calculated in Step 3 above
(Equation 14). From a practical standpoint, a value two or
three times VDS(norm) expected under normal operation will
prove to be a good starting point for VDS(min).
8. Select a value of RT less than 1.0 M
for minimal timing
error whose value is compatible with RX (RX will be selected
in Step 9 below). A recommended starting value to use for RT
would be 470 k. The consideration here is that the input
impedance of the threshold comparators are approximately
10 M
and if RT values greater than 1.0 M
are used,
significant timing errors may be experienced as a result of
input bias current variations of the threshold comparators.
9. Select a value of RX which is compatible with RT. The
value of RX should be between 50 k and 100 k. Recall in
Equation 5 that VDS(min) was determined by the combined
selection of RX and RT. Low values of RX will give large
values for K (K = 4.0
μ
A/V2 for RX = 50 k) causing ISQ to be
very sensitive to VDS variations (see Equation 1). This is
desirable if a minimum VDS trip point is needed in the 1.0 V
range since small VDS values will generate measurable
currents. However, at high VDS values, TMOS device
currents become excessively large and the current squaring
function begins to deviate slightly from the predicted value
due to high level injection effects occurring in the output PNP
of the current squaring circuit. These effects can be seen
when ISQ exceeds several hundred microamps. See
Figure 22 for graphical aid in the selection of RT and RX.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| MC33091AD | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:HIGH-SIDE TMOS DRIVER |
| MC33091AP | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:HIGH-SIDE TMOS DRIVER |
| MC33092 | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:LINEAR INTEGRATED CIRCUIT |
| MC33092A | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:ALTERNATOR VOLTAGE REGULATOR |
| MC33092ADW | 制造商:Motorola Inc 功能描述:AUTOMOTIVE, AUTOMOTIVE VOLTAGE REGULATOR, 20 Pin, Plastic, SOP 制造商:Freescale Semiconductor 功能描述:IC |
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