LTC1255C View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1255C

Dual 24V High-Side MOSFET Driver

Linear Technology 

UU W U

APPLICATIO S I FOR ATIO

18V

VS

DS1

1/2 LTC1255

IN1

G1

GND

+

CDELAY

0.01µF RDELAY

100k

100µF

1N4148

RSENSE

0.036Ω

IRF530

12V

LOAD

LTC1255 • F06

Figure 6. Using a Speed-Up Diode

Current Limited Power Supplies

The LTC1255 requires at least 3.5V at the supply pin to

ensure proper operation. It is therefore necessary that

the supply to the LTC1255 be held higher than 3.5V at

all times, even when the output of the switch is short

circuited to ground. The output voltage of a current

limited regulator may drop very quickly during short

circuit and pull the supply pin of the LTC1255 below

3.5V before the shutdown circuitry has had time to

respond and remove drive from the gate of the power

MOSFET. A supply filter should be added as shown in

Figure 7 which holds the supply pin of the LTC1255

high long enough for the overcurrent shutdown cir-

cuitry to respond and fully discharge the gate.

Linear regulators with small output capacitors are the

most difficult to protect as they can “switch” from a

voltage mode to a current limited mode very quickly.

15V

+

12V/2A

REGULATOR

10µF

+

47µF*

10Ω*

0.01µF

VS

DS1

1/2 LTC1255

IN1

G1

GND

+

100k

10µF

RSENSE

0.1Ω

1N4148

12V

MTP12N06E

*SUPPLY FILTER COMPONENT

LTC1255 • F07

SHORT

CIRCUIT

Figure 7. Supply Filter for Current Limited Supplies

LTC1255

The large output capacitors on many switching regula-

tors, on the other hand, may be able to hold the supply

pin of the LTC1255 above 3.5V sufficiently long that this

extra filtering is not required.

Because the LTC1255 is micropower in both the standby

and ON state, the voltage drop across the supply filter

is very small (typically < 6mV) and does not signifi-

cantly alter the accuracy of the drain sense threshold

voltage which is typically 100mV.

AUTOMOTIVE APPLICATIONS

Reverse Battery Protection

The LTC1255 can be protected against reverse battery

conditions by connecting a resistor in series with the

ground lead as shown in Figure 8. The resistor limits the

supply current to less than 120mA with – 12V applied.

Since the LTC1255 draws very little current while in

normal operation, the drop across the ground resistor

is minimal. The 5V µP (or controlling logic) is protected

by the 10k resistors in series with the input.

5V

µp OR

CONTROL

LOGIC

14V

+

28V

10µF

VS

DS1

1/2 LTC1255

10k

IN1

G1

GND

12V

RSENSE

0.036Ω

MTP12N06E

100Ω

LOAD

LTC1255 • F08

Figure 8. Reverse Battery Protection

Transient Overvoltage Protection

A common scheme used to limit overvoltage transients

on a 14V nominal automotive power bus is to clamp the

supply to the module containing the high-side MOSFET

switches with a large transient suppressor diode, D1 in

Figure 9. This diode limits the supply voltage to 40V

under worse case conditions. The LTC1255 is designed

to survive short (10ms) 40V transients and return to

normal operation after the transient has passed.

9

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