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参数资料
| 型号： | MSK5200ZU |
| 厂商： | Electronic Theatre Controls, Inc. |
| 英文描述： | DUAL POSITIVE/NEGATIVE 3 AMP, ULTRA LOW DROPOUT FIXED VOLTAGE REGULATORS |
| 中文描述： | 双正/负3安培，低压差电压调节器超定额 |
| 文件页数： | 3/5页 |
| 文件大小： | 250K |
| 代理商： | MSK5200ZU |
APPLICATION NOTES
HEAT SINKING:
To determine if a heat sink is required for your application
and if so, what type, refer to the thermal model and governing
equation below.
Governing Equation: Tj = Pd x (R
θ
jc + R
θ
cs + R
θ
sa) + Ta
WHERE
Tj = Junction Temperature
Pd = Total Power Dissipation
R
θ
j = Junction to Case Thermal Resistance
R
θ
cs = Case to Heat Sink Thermal Resistance
R
θ
sa = Heat Sink to Ambient Thermal Resistance
Tc = Case Temperature
Ta = Ambient Temperature
Ts = Heat Sink Temperature
EXAMPLE:
This example demonstrates an analysis where each regulator is
at one-half of its maximum rated power dissipation, which oc-
curs when the output currents are at 1.5 amps each.
Conditions for MSK 5202:
Vin = ±7.0V; Iout = ±1.5A
1.) Assume 45° heat spreading model.
2.) Find positive regulator power dissipation:
Pd = (Vin - Vout)(Iout)
Pd = (7-5)(1.5)
Pd = 3.0W
3.) For conservative design, set Tj = +125°C Max.
4.) For this example, worst case Ta = +90°C.
5.) R
θ
jc = 2.5°C/W from the Electrical Specification Table.
6.) R
θ
cs = 0.15°C/W for most thermal greases.
7.) Rearrange governing equation to solve for R
θ
sa:
R
θ
sa= ((Tj - Ta)/Pd) - (R
θ
jc) - (R
θ
cs)
= (125°C - 90°C)/3.0W - (2.5°C/W) - ( 0.15°C/W)
= 9.15°C/W
The same exercise must be performed for the negative regula-
tor. In this case the result is 9.15°C/W. Therefore, a heat sink
with a thermal resistance of no more than 9.1°C/W must be
used in this application to maintain both regulator circuit junc-
tion temperatures under 125°C.
OVERLOAD SHUTDOWN:
The regulators feature both current and thermal overload
protection. When the maximum power dissipation is not ex-
ceeded, the regulators will current limit slightly above their 3
amp rating. As the Vin-Vout voltage increases, however, shut-
down occurs in relation to the maximum power dissipation curve.
If the device heats enough to exceed its rated die junction tem-
perature due to excessive ambient temperature, improper heat
sinking etc., the regulators also shutdown until an appropriate
junction temperature is maintained. It should also be noted
that in the case of an extreme overload, such as a sustained
direct short, the device may not be able to recover. In these
instances, the device must be shut off and power reapplied to
eliminate the shutdown condition.
LOAD REGULATION:
For best results the ground pin should be connected directly
to the load as shown below. This effectively reduces the ground
loop effect and eliminates excessive voltage drop in the sense
leg. It is also important to keep the output connection between
the regulator and the load as short as possible since this di-
rectly affects the load regulation. If 20 gauge wire were used
as an example, which has a resistance of about .008 ohms per
foot, this would result in a drop of 8mV/ft at 1Amp of load
current. It is also important to follow the capacitor selection
guidelines to achieve best performance. Refer to Figure 2 for
connection diagram.
FIGURE 2
Avoiding Ground Loops
BYPASS CAPACITORS:
For most applications a 20uF, tantalum capacitor should be
attached as close to the regulator's output as possible. This
will effectively lower the regulator's output impedance, improve
transient response and eliminate any oscillations that may be
normally associated with low dropout regulators. Additional
bypass capacitors can be used at the remote load locations to
further improve regulation. These can be either of the tantalum
or the electrolytic variety. Unless the regulator is located very
close to the power supply filter capacitor(s), a 4.7uF minimum
tantalum capacitor should also be added to the regulator's in-
put. An electrolytic may also be substituted if desired. When
substituting electrolytic in place of tantalum capacitors, a good
rule of thumb to follow is to increase the size of the electrolytic
by a factor of 10 over the tantalum value.
Low Dropout Positive and Negative Power Supply
MSK 5202 TYPICAL APPLICATION:
FIGURE 1
3
Rev. C 7/00
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