LTC1155 查看數據表（PDF） - Linear Technology

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LTC1155

Dual High Side Micropower MOSFET Driver

Linear Technology 

LTC1155

APPLICATI S I FOR ATIO

VS = 5.0V

VS

DS1

IN1 LTC1155

CDLY

0.22µF

RDLY

270k

D1

1N4148

RSEN

0.025Ω

GND

G1

IRLZ34

GND

LOAD

1155 F03

Figure 3. Using a Speed-Up Diode

sense pin and dramatically reducing the amount of time

the MOSFET is in an overload condition. The drain sense

resistor value is selected to limit the maximum DC current

to 4A. Above 28A, the delay time drops to 10µs.

Switched Supply Applications

Large inductive loads, such as solenoids, relays and

motors store energy which must be directed back to either

the power supply or to ground when the supply voltage is

interrupted (see Figure 4). In normal operation, when the

switch is turned OFF, the energy stored in the inductor is

harmlessly absorbed by the MOSFET; i.e., the current

flows out of the supply through the MOSFET until the

inductor current falls to zero.

If the MOSFET is turned ON and the power supply (battery)

removed, the inductor current is delivered by the supply

capacitor. The supply capacitor must be large enough to

deliver the energy demanded by the discharging inductor.

If the storage capacitor is too small, the supply lead of the

LTC1155 may be pulled below ground, permanently

destroying the device.

Consider the case of a load inductance of 1mH which is

supporting 3A when the 6V power supply connection is

interrupted. A supply capacitor of at least 250µF is

required to prevent the supply lead of the LTC1155 from

being pulled below ground (along with any other circuitry

tied to the supply).

Any wire between the power MOSFET source and the load

will add a small amount of parasitic inductance in series

with the load (approximately 0.4µH/foot). Bypass the

power supply lead of the LTC1155 with a minimum of

10µF to ensure that this parasitic load inductance is

discharged safely, even if the load is otherwise resistive.

Large Inductive Loads

Large inductive loads (>0.1mH) may require diodes con-

nected directly across the inductor to safely divert the

stored energy to ground. Many inductive loads have these

diodes included. If not, a diode of the proper current rating

should be connected across the load to safely divert the

stored energy.

+

+

CS

CDLY

RSEN

0.025Ω

VS

DS1

IN1 LTC1155

G1

GND

RDLY

GND

Figure 4. Switched Supply

IRLZ34

L LOAD

1155 F04

Reverse-Battery Protection

The LTC1155 can be protected against reverse-battery

conditions by connecting a resistor in series with the

ground lead as shown in Figure 5. The resistor limits the

supply current to less than 50mA with –12V applied. Since

the LTC1155 draws very little current while in normal

operation, the drop across the ground resistor is minimal.

The TTL or CMOS driving logic is protected against

reverse-battery conditions by the 100k input current lim-

iting resistor. The addition of 100k resistance in series

with the input pin will not affect the turn ON and turn OFF

times which are dominated by the controlled gate charge

and discharge periods.

8

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