MIC2025(2000) View Datasheet(PDF) - Micrel

Part Name

Description

MFG CO.

MIC2025
(Rev.:2000)

Single-Channel Power Distribution Switch

Micrel 

MIC2025/2075

Block Diagram

Micrel

EN

OSC.

THERMAL

SHUTDOWN

UVLO

1.2V

REFERENCE

IN

CHARGE

PUMP

GATE

CONTROL

CURRENT

LIMIT

FLAG

RESPONSE

DELAY

OUT

FLG

GND

Functional Description

Input and Output

IN is the power supply connection to the logic circuitry and the

drain of the output MOSFET. OUT is the source of the output

MOSFET. In a typical circuit, current flows from IN to OUT

toward the load. If VOUT is greater than VIN, current will flow

from OUT to IN since the switch is bidirectional when en-

abled. 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 (VOUT > VIN) when the

switch is disabled. In this situation, the MIC2025/75 avoids

undesirable current flow from OUT to IN.

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. Each channel employs its

own thermal sensor. Thermal shutdown shuts off the output

MOSFET and asserts the FLG output if the die temperature

reaches 140°C. The MIC2025 will automatically reset its

output should the die temperature cool down to 120°C. The

MIC2025 output and FLG signal will continue to cycle on and

off until the device is disabled or the fault is removed. Figure

2 depicts typical timing. If the MIC2075 goes into thermal

shutdown, its output will latch off and a pull-up current source

is activated. This allows the output latch to automatically reset

when the load (such as a USB device) is removed. The output

can also be reset by toggling EN. Refer to Figure 1 for details.

Depending on PCB layout, package, ambient temperature,

etc., it may take several hundred milliseconds from the

incidence of the fault to the output MOSFET being shut off.

The worst-case scenario of thermal shutdown is that of a

short-circuit fault and is shown in the in the “Function Char-

acteristics: Thermal Shutdown Response” graph.

Power Dissipation

The device’s junction temperature depends on several fac-

tors such as the load, PCB layout, ambient temperature and

package type. Equations that can be used to calculate power

dissipation of each channel and junction temperature are

found below.

PD = RDS(on) × IOUT2

Total power dissipation of the device will be the summation of

PD for both channels. To relate this to junction temperature,

the following equation can be used:

TJ = PD × θJA + TA

where:

TJ = junction temperature

TA = ambient temperature

θJA = is the thermal resistance of the package

Current Sensing and Limiting

The current-limit threshold is preset internally. The preset

level prevents damage to the device and external load but still

allows a minimum current of 500mA to be delivered to the

load.

The current-limit circuit senses a portion of the output MOS-

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 three scenarios:

Switch Enabled into Short-Circuit

If a switch is enabled into a heavy load or short-circuit, the

switch immediately enters into a constant-current mode,

reducing the output voltage. The FLG signal is asserted

indicating an overcurrent condition. See the Short-Circuit

Response graph under Functional Characteristics.

March 2000

9

MIC2025/2075

Share Link: