MIC2010_05 Datasheet, PDF (7/13 Pages) Micrel Semiconductor – USB Power Controller

MIC2010/2070
Functional Diagram
EN
S3#
MAIN
Current
Limit
MAIN
FET
Charge Pump
+
Gate Control
AUX
FET
Thermal
Sense
Current
Limit
OUT
AUX
RSET
Micrel
*MIC2070-1/2 Only
To Other Channel
Latch
10ms
Timer
AUX
*
* 'P' options only
/FAULT
Functional Description
The MIC2010/2070 are designed to support the power distri-
bution requirements for USB wakeup from the ACPI S3 state.
It integrates two independent channels under control of input
S3#. When S3# is asserted LOW (ACPI S3 state) the MIC2010/
2070 will switch a 500mΩ MOSFET switch from the AUX
input to each of its two outputs. In addition the current-limit
threshold will be set to a value specified by a resistor
connected to the RSET inputs. Conversely when the S3#
input is HIGH the MIC2010/2070 will switch a 100mΩ MOSFET
switch from the MAIN inputs to each of its two outputs. The
current-limit threshold is preset to 500mA in this state. The
lower current limit during the ACPI S3 state helps to ensure
that the standby supply maintains regulation even during fault
conditions.
Thermal Shutdown
Thermal shutdown is employed to protect the device from
damage should the die temperature exceed safe margins
due mainly to short circuit faults. Thermal shutdown shuts off
the output MOSFET and asserts the FAULT output if the die
temperature reaches 140°C and the overheated channel is in
current limit. The other channel is not affected. If however, the
die temperature exceeds 160°C, both channels will be shut
off even if neither channel is in current limit.
Power Dissipation
The device’s junction temperature depends on several fac-
tors such as the load, PCB layout, ambient temperature and
package type. The power dissipated in each channel is
P_D = R_DS(on) × I_OUT2 where R_DS(on) is the on-resistance of the
internal MOSFETs and I_OUT is the continuous output current.
Total power dissipation of the device will be the summation of
P_D for both channels. To relate this to junction temperature,
the following equation can be used:
TJ = P_D × θ_JA + T_A
where:
T_J = junction temperature
T_A = ambient temperature
θ_JA = is the thermal resistance of the package
Current Sensing and Limiting
The current-limit threshold of each channel is preset inter-
nally at 500mA when S3# is deasserted. When S3# is
asserted the current-limit threshold is specified by a resistor
connected to the RSET input. The value of the current-limit
threshold is determined by the equation 18/R_SET ohms where
R_SET is the resistance connected between the RSET pin and
ground. The current-limit threshold should be set at 1.2X of
the applications continous output current requirement.
When an overcurrent condition lasts longer than t_DLY the
MIC2070 will activate an internal circuit breaker that will latch
the output off and assert FAULT. The output will remain off
until either the load is removed or EN is toggled. When the
MIC2070 enters a latched output condition a 1mA pull-up
current source is activated. This provides a way to automati-
cally reset the output once the load is removed without the
need to toggle the enable input. Please refer to Figure 7 for
timing details.
The MIC2010 will automatically reset its output when the die
temperature cools down to 120°C. The MIC2010 output and
FAULT signal will continue to cycle on and off until the device
is disabled or the fault is removed. Figure 6 depicts typical
timing. Depending on PCB layout, package, ambient tem-
perature, etc., it may take several hundred milliseconds from
the incidence of the fault to the output MOSFET being shut
January 2005
7
M9999-101104