January 2005

7

M9999-101104

MIC2010/2070

Micrel

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

internal MOSFETs and I

Total power dissipation of the device will be the summation of

P

the following equation can be used:

Functional Diagram

Current

Limit

10ms

Timer

Charge Pump

+

Gate Control

S3#

EN

Current

Limit

MAIN

OUT

AUX

RSET

/FAULT

AUX

Latch

To Other Channel

*

MAIN

FET

AUX

FET

*MIC2070-1/2 Only

Thermal

Sense

* 'P' options only

TJ = P

where:

T

T

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

R

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

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