Triple 1.2A USB Switch in 4mm x 4mm

Thin QFN

8

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device operates in continuous current-limit mode and

limits output current to a user-programmable level.

short-circuit current-limit mode and pulses the output

current to levels that are 30% (typ) higher than the

selected current limit. When either fault condition per-

sists for 20ms (typ), the output turns off and its fault flag

is asserted. The output automatically restarts 20ms

after the short or overload is removed.

Auto-Restart Mode

The MAX1564 detects short-circuit removal by sourcing

25mA from the output and monitoring the output volt-

age. When the voltage at the output exceeds 0.5V for

20ms, the fault flag resets, the output turns back on,

and the 25mA current source turns off. Active loads are

not expected to draw measurable current when sup-

plied with less than 0.5V. The MAX1564 can also be

reset from a fault by toggling the ON_ input for the

offending channel.

Reverse Current Blocking

The USB specification does not allow an output device

to source current back into the USB port. However, the

MAX1564 is designed to safely power noncompliant

devices. During normal operation with the channel

enabled, the IC immediately turns off the switch if the

output voltage rises above the input voltage sufficiently

to create a reverse current in excess of 0.9A (typ). If the

output voltage condition persists for longer than 20ms

(typ), the switch remains off and the FLT_ flag is assert-

ed. When any channel is disabled, the output is

switched to a high-impedance state, blocking reverse

current flow from the output back to the input.

Thermal Shutdown

Independent thermal shutdown of each channel per-

mits delivering power to normal loads even if one load

has a fault condition. The thermal limit does not have

the 20ms fault blanking but sets the same fault latch

that is used for other faults. Exiting this latched state is

described in the Auto-Restart Mode section.

Fault Indicators and Fault Blanking

The MAX1564 provides an independent open-drain

fault output (FLT_) for each switch. Connect FLT_ to IN_

through a 100k

Ω pullup resistor for most applications.

FLT_ asserts low when any of the following conditions

occur:

• The input voltage is below the UVLO threshold.

• The switch junction temperature exceeds the +160°C

thermal-shutdown temperature limit.

• The switch is in current-limit or short-circuit current-

limit mode after the fault-blanking period (20ms typ)

expires.

• The reverse current condition exists after the fault-

blanking period expires.

The FLT_ output goes high impedance after a 20ms

delay once the fault condition is removed. Ensure that

the MAX1564 input bypass capacitance prevents

glitches from triggering the FLT_ outputs. To differenti-

ate large capacitive loads from short circuits or sus-

tained overloads, the MAX1564 has an independent

fault-blanking circuit for each switch. When a load tran-

sient causes the output to enter current limit, an internal

counter monitors the duration of the fault. For load

faults exceeding the 20ms fault-blanking time, the

switch turns off, FLT_ asserts low, and the output enters

auto-restart mode (see the Current-Limit Fault

Protection and Auto-Restart Mode sections). Only cur-

rent-limit and short-circuit faults are blanked. Thermal-

overload faults and input voltages below the UVLO

threshold immediately turn off the offending output and

assert FLT_ low.

Fault blanking allows the MAX1564 to handle USB

loads that might not be fully compliant with USB

specifications. The MAX1564 successfully powers USB

MAX1564

INA

1

3

4

2

5

16

15

14

6

11

9

10

12

8

7

13

INB

INC

VCC

SEL

OUTA

OUTB

OUTC

ONA

ONB

ONC

FLTA

FLTB

FLTC

R2

100k

Ω

R3

100k

Ω

R1

26.1k

Ω

R4

100k

Ω

C2

1

µF

C1

0.1

µF

C3

1

µF

C4

1

µF

SETI

INPUT

2.75V TO 5.5V

USB

PORT A

USB

PORT B

USB

PORT C

GND

ACTIVE-HIGH/

ACTIVE-LOW

SELECT INPUT

Figure 1. Typical Application Circuit