ramps down for 800µs. Under fault conditions, the output

of the switches turns off rapidly to provide maximum safe-

ty for the upstream power source and downstream

devices. Internal blocks shut down to minimize supply

current when the switch is off.

Layout and Thermal Dissipation

Keep all traces as short as possible to reduce the effect

of undesirable parasitic inductance and optimize the

switch response time to output short-circuit conditions.

Place the input and output capacitors no more than

5mm from the device leads. Connect IN and OUT to the

power bus with short traces. Wide power bus planes at

IN and OUT provide superior heat dissipation.

Calculate the power dissipation for a normal loaded

condition as follows:

At a 3A operating current and the maximum on-resis-

tance of the switch (50m

Ω), the power dissipation is:

Ω = 450mW

The worst-case power dissipation occurs when the out-

put current is just below the current-limit threshold (set

to 3A in this example) with an output voltage greater

than +1V. In this case, the power dissipated in the

switch is the voltage drop across the switch multiplied

by the current limit:

For a +5V input and +1V output, the maximum power

dissipation is:

P = 3A x (5V - 1V) = 12W

Because the package power dissipation is 471mW for

the MAX1562/MAX1562H and 1.35W for the MAX1563,

the devices’ die temperature exceeds the +160°C ther-

mal-shutdown threshold, and the switch output shuts

down until the junction temperature cools by 15°C. The

duty cycle and period are strong functions of the ambi-

ent temperature and the PC board layout.

If the output current exceeds the current-limit threshold,

or the output voltage is pulled below the short-circuit

detect threshold, the MAX1562/MAX1562H/MAX1563

enter a fault state for 20ms, after which autoreset mode

is enabled and 25mA is sourced by the output. For a

+5V input, OUT short-circuited to GND, and autoreset

mode active, the power dissipation is as follows:

P = 0.025A x 5V = 0.125W

Programmable 4A USB Current-Limited

Switches with Autoreset and Fault Blanking

10

______________________________________________________________________________________

MAX1563

FAULT

OUT

OUT

ISET

SEL

ON

IN

IN

USB

PORT

GND

INPUT

+4V TO +5.5V

OFF

ON

1

µF

4.7

µF*

100k

Ω

*USB APPLICATIONS MAY REQUIRE

ADDITIONAL BULK CAPACITANCE.

Typical Application Circuit

CHARGE

PUMP

THERMAL

SHUTDOWN

FAULT LOGIC

20ms TIMERS

ILIM

25mA

ULVO

OSC

25kHz

REF

BIAS

ON

SEL

IN

MAX1563

OUT

GND

FAULT

IN

MAX1563 Functional Diagram

TOP VIEW

() FOR MAX1562H.

OUT

IN

ISET

1

2

8

7

OUT

IN

FAULT

GND

ON (ON)

SO

3

4

6

5

MAX1562

MAX1562H

IN

N.C.

OUT

IN

N.C.

ISET

ON

FAULT

GND

OUT

N.C.

SEL

12

11

10

45

6

1

+

+

2

3

9

8

7

MAX1563

THIN QFN

4 mm x 4 mm

Pin Configurations