MIC2012 Datasheet, PDF (8/10 Pages) Micrel Semiconductor – USB Power Controller Advance Information

MIC2012
Functional Diagram
EN
S3#
MAIN
Current
Limit
MAIN
FET
Charge Pump
+
Gate Control
AUX
FET
Thermal
Sense
Current
Limit
OUT
AUX
Micrel
*MIC2070-1/2 Only
To Other Channel
Latch
10ms
Timer
AUX
*
* 'P' options only
/FAULT
Functional Description
The MIC2012/2072 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 (S3 state) the MIC2012/
2072 will switch a 500mΩ, 100mA MOSFET switch from the
AUX input to each of its two outputs. Conversely when the
S3# input is HIGH (S0 state) the MIC2012/72 will switch a
100mΩ, 500mA MOSFET switch from the MAIN input to each
of its two outputs. 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 thresholds are preset internally for each
state. The preset level prevents damage to the device and
external load but still allows a minimum current of 100mA or
500mA to be delivered to the load depending on the state of
the device according to the S3# input. When S3# is LOW the
current-limit is set at 100mA minimum. When S3# is HIGH the
current-limit is set at 500mA minimum.
Should an over-current condition last longer than t_DLY, the
MIC2072 will latch the faulty output off. The output will remain
off until either the load is removed or the EN signal (MIC2072-
1, -2) is toggled. When the MIC2072 enters a latched output
condition a 1mA pull-up current source is activated. This
provides a way to automatically reset the output once the load
is removed without the need to toggle the enable input such
as in the MIC2072. Please refer to Figure 7 for timing details.
The MIC2012 will automatically reset its output when the die
temperature cools down to 120°C. The MIC2012 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
off. This time duration will be shortest in the case of a dead
short on the output.
MIC2012/2072
8
September 2000