 2002-2012 Microchip Technology Inc.

DS21446D-page 15

TC646

FIGURE 5-8:

Power the Fan from a -12V Supply.

TABLE 5-2:

5.6

Latch-up Considerations

As with any CMOS IC, the potential exists for latch-up

if signals are applied to the device which are outside

the power supply range. This is of particular concern

during power-up if the external circuitry (such as the

powered by a supply different from that of the TC646.

supply powers up first. If possible, the networks

ply at the same physical location as the IC itself. Even

if the IC and any external networks are powered by the

same supply, physical separation of the connecting

points can result in enough parasitic capacitance and/

or inductance in the power supply connections to delay

one power supply “routing” versus another.

5.7

Power Supply Routing and

Bypassing

erroneous operation of the FAULT output. As a result,

these inputs should be bypassed with a 0.01 µF

capacitor mounted as close to the package as possible.

from a high impedance source (such as a thermistor).

1 µF capacitor. Grounds should be kept as short as

possible. To keep fan noise off the TC646 ground pin,

individual ground returns for the TC646 and the low

side of the fan current sense resistor should be used.

Device

Package

(V)

(V)

Fan Current

(mA)

Suggested

MMBT2222A

SOT-23

1.2

50

40

150

800

MPS2222A

TO-92

1.2

50

40

150

800

MPS6602

TO-92

1.2

50

40

500

301

SI2302

SOT-23

2.5

NA

20

500

Note 1

MGSF1N02E

SOT-23

2.5

NA

20

500

Note 1

SI4410

SO-8

4.5

NA

30

1000

Note 1

SI2308

SOT-23

4.5

NA

60

500

Note 1

Note 1: A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.

GND

+5V

-12V

TC646

Fan

2.2 k

Ω

2.2

Ω

10 k

Ω

12.0V

Zener

NOTE: *Value depends on the specific application and is shown for example only.