SC283EVB datasheet(13/20 Pages) SEMTECH

13 / 20 page

SC283

Applications Information (continued)

and 3b show the maximum allowable load current based

upon the limit of maximum loss for V

IN=3.3V and VIN=5.0V,

respectively. The curves are drawn for high duty-cycle

operation. If the operating duty-cycle is lower, the loss is

lower allowing higher load current.

SC283 Maximum Loss for T

J=125°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Loss of Channel A (W)

TA= 25°C

TA= 85°C

TA= 55°C

Figure 2 — Maximum allowable loss for each channel

for a maximum junction temperature of 125°C

Protection Features

The SC283 provides the following protection features:

Current Limit

Over-Voltage Protection

Soft-Start Operation

Thermal Shutdown

Current Limit and Protection

The internal PMOS power device in the switching stage

is protected by a current limit feature. If the inductor

current is above the PMOS current limit for 16 consecutive

cycles, the part enters foldback current limit mode and

the output current is limited to the current limit holding

current (I

CL_HOLD) of a few hundred milliampere. Under

this condition, the output voltage will be the product

of I

CL_HOLD and the load resistance. The

current limit

holding current will decrease when the output voltage

increases. The load presented must fall below the current

limit holding current for the part to exit foldback current

limit mode. Figure 4 shows how the typical current limit

holding current varies with output voltage. The SC283 is

capable of sustaining an indefinite short circuit without

damage and will resume normal operation when the fault

is removed. The foldback current limit mode is disabled

during soft-start. Current limit functionality is shown in

Figure 6.

•

SC283 Maximum Load Current for T

J=125°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Load Current of Channel A (A)

TA  42°C

TA= 85°C

TA= 60°C

VIN= 3.3V

VOUT= 2.5V

(a) V

IN= 3.3V, VOUT=2.5V

SC283 Maximum Load Current for T

J=125°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Load Current of Channel A (A)

TA  47°C

TA= 85°C

TA= 70°C

VIN= 5.0V

VOUT= 3.3V

(b) V

IN= 5.0V, VOUT=3.3V

Figure 3 — Maximum allowable Load Current for each

channel for a maximum junction temperature of 125°C

Current Limit Holding Current over Vout

100

150

200

250

300

1.0

1.5

2.0

2.5

3.0

3.5

Output Voltage (V)

TA= 25°C

VIN= 5.0V

VIN= 3.6V

VIN= 3.3V

Figure 4 — Typical Current Limit Holding Current

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