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参数资料
| 型号： | MAX1838 |
| 厂商： | Maxim Integrated Products, Inc. |
| 英文描述： | Dual USB Switch with Fault Blanking and Autoreset |
| 中文描述： | 双路USB开关，带有故障屏蔽及自复位功能 |
| 文件页数： | 9/12页 |
| 文件大小： | 639K |
| 代理商： | MAX1838 |
Output Fault Protection
The MAX1838 senses the switch output voltage and
selects 0.9A continuous current limiting when V
OUT
is
greater than 1V or short-circuit current limiting when
V
OUT
is less than 1V (see
Behavior During Current Limit
and Fault Blanking
).
Autoreset Mode
The MAX1838 monitors the output to detect an over-
load condition. If an output fault is detected for more
than the 20ms blanking time, OUT_ latches,
FAULT
goes low, and OUT sources 25mA to the load. If the
voltage at OUT exceeds 0.5V for 20ms, the fault resets,
the 25mA current source shuts down, and the channel
turns back on. For proper autoreset function, the output
load current must remain below 25mA when the output
voltage is lower than 0.5V. Toggle
ON
to manually reset
the output.
Thermal Shutdown
The MAX1838 features independent thermal shutdown
for each channel, allowing one channel to deliver
power even if the other channel has a fault condition.
When the junction temperature exceeds +160
°
C, the
switch turns off and
FAULT_
goes low immediately.
Fault blanking does not occur during thermal limit.
When the junction cools by 15
°
C, the channel turns on
again. If the fault overload condition continues, the
channel cycles on and off, resulting in a pulsed output.
Fault Indicators
The MAX1838 provides an open-drain fault output
(
FAULT
) for each channel. For most applications, con-
nect
FAULT
to AUX through a 100k
pullup resistor.
FAULT
goes low when any one of the following condi-
tions occurs:
V
AUX
_ is below the undervoltage-lockout (UVLO)
threshold.
V
IN
_ is below the undervoltage-lockout threshold
and SEL = AUX.
The switch junction temperature exceeds the thermal
shutdown temperature limit of +160
°
C.
The switch is in current-limit or short-circuit limit
mode after the fault-blanking period is exceeded
(autoreset).
After the fault condition is removed, the
FAULT
output
deasserts after a 20ms delay. Ensure that the MAX1838
has adequate input bypass capacitance to prevent
glitches from triggering
FAULT
outputs. Input glitches
greater than 0.2V/μs may cause erroneous
FAULT
indi-
cations.
Programmable Current Limit
When using the auxiliary input (AUX), each channel has
an adjustable current limit. For maximum current limit
(0.9A), open ADJ. For current limits below 0.9A, con-
nect a resistor from ADJ to GND according to the fol-
lowing equation:
I
OUT
_ = 0.9A
×
R
ADJ
/ (200k
+ R
ADJ
)
Behavior During Current Limit
and Fault Blanking
The MAX1838 limits switch current in the following
ways. When
ON
is high, both channels are off. When
ON
is low, both channels can supply a continuous out-
put current of at least 500mA. When the output current
exceeds the 0.9A threshold, the MAX1838 will limit the
current depending on the output voltage. If V
OUT
is
greater than 1V (current-limit mode), the MAX1838 reg-
ulates the output current to 0.9A. If V
OUT
is less than 1V
(short-circuit mode), the MAX1838 pulses the output,
decreasing the current to 0.35A
RMS
(Table 2). Note that
a thermal overload may result from either of these high-
current conditions.
The MAX1838 switches may enter current limit in nor-
mal operation when powering up or driving heavy
capacitive loads. To differentiate these conditions from
short circuits or sustained overloads that may damage
the device, the MAX1838 has an independent fault-
blanking circuit in each channel. When a load transient
causes the device to enter current limit, an internal
counter starts to monitor the duration of the fault. If the
load fault persists beyond the 20ms fault-blanking time,
the channel turns off,
FAULT
asserts low, and the chan-
nel enters autoreset mode (see
Autoreset Mode
). Only
current-limit and short-circuit faults are blanked.
Thermal overload faults and input undervoltage imme-
diately cause the channel to turn off and
FAULT
to
assert low.
Fault blanking allows the MAX1838 to accommodate
USB loads that may not be fully compliant with the USB
specifications. USB loads with additional bypass
capacitance and/or large startup currents can be suc-
cessfully powered while protecting the upstream power
source. If the switch is able to bring up the load within
the 20ms blanking period, no fault is indicated.
Switching Supplies
To select IN as the source for both channels, drive SEL to
a logic high. To select AUX, drive SEL low. To minimize
switching transients, the MAX1838 switches between
input supplies (IN and AUX) with a make-before-break
sequence. Both switches are on simultaneously for up to
9ms before the initial supply is disconnected. When
switching from IN to AUX, a significant current may flow
M
Dual USB Switch with Fault Blanking
and Autoreset
_______________________________________________________________________________________
9
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| MAX1838EEE+T | 功能描述:电源开关 IC - USB Dual USB Switch w/Fault Blank RoHS:否 制造商:Micrel 电源电压-最小:2.7 V 电源电压-最大:5.5 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:SOIC-8 封装:Tube |
| MAX1838EEE-T | 功能描述:电源开关 IC - USB Dual USB Switch w/Fault Blank RoHS:否 制造商:Micrel 电源电压-最小:2.7 V 电源电压-最大:5.5 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:SOIC-8 封装:Tube |
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