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參數(shù)資料
| 型號： | AMS2027S |
| 廠商： | Advanced Monolithic Systems, Inc. |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | SINGLE POWER DISTRIBUTION SWITCH |
| 中文描述： | 單電源配置開關(guān) |
| 文件頁數(shù)： | 4/5頁 |
| 文件大小： | 46K |
| 代理商： | AMS2027S |
Advanced Monolithic Systems, Inc.
6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS2027
APPLICATION HINTS
Power Supply Considerations
A 0.047
μ
F ceramic bypass capacitor close to the device, between
input and ground is recommended. When the output load is heavy
or has large paralleled capacitors, a high value electrolytic
capacitor should be used. To improve the immunity of the device
to ESD, use a 0.1
μ
F ceramic capacitor to bypass the output.
Current Limit
A sense FET monitors overcurrent conditions. When an
overcurrent condition is detected the device maintains a constant
output current and decreases the voltage accordingly. If the
condition is present long enough to activate the thermal limiting
the result is the shutdown of the device.
There are three situation in which overload can occur. In the first
case, the output has been shorted before the device is enabled or
before V
I
has been applied. The device senses the short and
switches into a constant-current output.
In the second case, the short occurs while the device is enabled.
When this happens, very high currents flow for a short time
before the current-limit circuit can react. After the current-limit
circuit has tripped, the device limits normally.
In the third case, the load has been gradually increased beyond
the recommended operating current. The current will rise until
the current-limit threshold is reached. The AMS2027 is able to
deliver current up to the current-limit threshold without damage.
When the threshold has been reached the device switches into the
constant current mode. When over current condition is detected
the error flag logic output remains low until the condition is
removed.
Power Dissipation and Junction Temperature
The thermal resistance of the surface-mount packages such as
SOIC is high compared to that of power packages. The use of the
N-cannel MOSFET which has low on-resistance, makes it
possible for small surface-mount packages to pass large currents.
To determine the power dissipation and junction temperature the
first step is to find r
ON
at the input voltage and operating
temperature.
As an initial estimate use the highest operating ambient
temperature of interest and read r
ON
from Figure1. Power
dissipation is equal to:
P
D
= r
ON
X I
2
Calculate the junction temperature:
T
J
= P
D
X R
θ
JA
+ T
A
Where R
θ
JA
is the thermal resistance and is 172
°
C/W for the
SOIC package. Compare the calculated junction temperature with
the initial estimate and if they don’t mach within a few degrees,
repeat the calculations using the calculated value as the new
estimate. A few repetitions will be sufficient to give a reasonable
answer.
Thermal Protection
Thermal protection prevents damage to the device when over
load or short circuits conditions are present for extended periods
of time. These conditions force the AMS2027 into the constant
current mode. As a result the voltage across the high-side switch
will increase. Under short-circuit conditions the voltage across
the switch is equal to the input voltage. Continuous heavy over
loads and short circuits increase the power dissipation in the
switch and causes the junction temperature to rise to dangerously
high levels. The protection circuit shuts off the switch when it
senses the high junction temperature. The switch remains off
until the device has cooled about 20
°
C. The switch continues to
cycle off and on until the fault is removed.
Undervoltage Lock-out
An undervoltage lock-out is provided to insure that the switch is
in the off state at start-up. When the input voltage falls below
3.2V the switch will be turned off immediately. This will make it
easy for designers of hot plug-in systems that may not be able to
turn the switch off before removing the input power. In such
cases when the device is reinserted, the turn on will have a
controlled rise time to reduce EMI and voltage overshoots.
Figure 1
TYPICAL APPLICATIONS
POWER SUPPLY
4.0V - 5.0V
0.1
μ
F
1
μ
F
1
2
3
10k
EXTERNAL LOAD
0.1
μ
F
ENABLE
ERROR FLAG
7
8
6
IN
OUT
OUT
EN
ERROR
GND
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