MIC2537-1YM TR Micrel Inc, MIC2537-1YM TR Datasheet - Page 8

• Manufacturer Part Number: MIC2537-1YM TR
• Description: Quad USB Switch ( )
• Manufacturer: Micrel Inc
• Type: USB Switchr

Specifications of MIC2537-1YM TR

• Number Of Outputs: 4
• Rds (on): 700 mOhm
• Internal Switch(s): Yes
• Current Limit: 250mA
• Voltage - Input: 3 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MIC2537-1YMTR; MIC2537-1YMTR

MIC2537
Functional Description
The MIC2537-1 and MIC2537-2 are quad high-side switches
with active-high and active-low enable inputs, respectively.
Fault conditions turn off or inhibit turn-on of one or more of the
output transistors, depending upon the type of fault, and
activate the open-drain error flag transistors making them
sink current to ground.
Input and Output
IN (input) is the power supply connection to the logic circuitry
and the drain of each output MOSFET. OUTx (output) is the
source of each respective MOSFET. In a typical circuit,
current flows through the switch from IN to OUTx toward the
load. If V
to IN since the MOSFET is bidirectional when on.
The output MOSFET and driver circuitry are also designed to
allow the MOSFET source to be externally forced to a higher
voltage than the drain (V
this situation, the MIC2537 prevents reverse current flow.
Thermal Shutdown
Thermal shutdown shuts off the affected output MOSFET
and signals the corresponding fault flags if the die tempera-
ture exceeds 135 C. 10 C of hysteresis prevents the switch
from turning on until the die temperature drops to 125 C.
Overtemperature detection functions only when at least one
switch is enabled.
Current-Limit Induced Thermal Shutdown
Internal circuitry increases the output MOSFET on-resis-
tance until the series combination of the MOSFET on-resis-
tance and the load impedance limits output current to ap-
proximately 200mA. The resulting increase in power dissipa-
tion may cause the shorted channel to go into thermal
shutdown. In addition, even though individual channels are
thermally isolated, it is possible they may shut down when an
adjacent channel is shorted. When this is undesirable, shut-
down of the channels not shorted can be avoided by exter-
nally responding to the fault and disabling the current limited
channel before the shutdown temperature is reached. The
delay between the flag indication of a current limit fault and
thermal shutdown will vary with ambient temperature, board
layout, and load impedance, but is typically several seconds.
The USB controller must therefore recognize a fault and
disable the appropriate channel within this time.
December 1999
OUT
is greater than V
OUTx
> V
IN
, current will flow from OUT
IN
) when the output is off. In
8
Current Sensing and Limiting
The current-limit threshold is preset internally. The preset
level prevents damage to the output MOSFET and external
load but allows a minimum current of 0.15A through the
output MOSFET of each channel.
The current-limit circuit senses a portion of the output FET
switch current. The current sense resistor shown in the block
diagram is virtual and has no voltage drop. The reaction to an
overcurrent condition varies with the following three sce-
narios:
Switch Enabled into Short Circuit
If a switch is powered on or enabled into an excessive load or
short circuit, the switch immediately goes into a constant-
current mode, slowly increasing the output voltage. The fault
flag goes low until the load is reduced.
Short Circuit Applied to Output
When a heavy load or short circuit is applied to an enabled
switch, a large transient current may flow until the current-
limit circuitry responds. Once this occurs, the device limits
current to less than the short circuit current-limit specification.
See the “Functional Characteristics: Current-Limit Transient
Response graph for details.
Current-Limit Response
The MIC2537 current-limit profile exhibits a small foldback
effect of approximately 100mA. Once this current-limit thresh-
old is exceeded the device enters constant-current mode.
This constant current is specified as the short-circuit current
limit in the “Electrical Characteristics” table. It is important to
note that the MIC2537 will deliver load current up to the
current-limit threshold. See the “Functional Characteristics:
Current-Limit Response” graph for details.
Fault Flag
FLGx is an open-drain N-channel MOSFET output. Fault
flags are active (low) for current limit or thermal shutdown.
Each flag output MOSFET is capable of sinking a 10mA load
to approximately 200mV above ground. Several FLGx pins
may be wired-NOR connected to a common pull-up resistor.
MIC2537
Micrel