MAX1922 Maxim, MAX1922 Datasheet - Page 7

• Manufacturer Part Number: MAX1922
• Description: The MAX1922 current-limited 70mΩ switch with built-in fault blanking provides an accurate, preset 1
• Manufacturer: Maxim

outputs. Input voltage glitches less than 150mV do not
cause a spurious OC output. Load-transient faults less
than 10ms (typ) will not cause an OC output assertion.
Only current-limit faults are blanked. Die overtempera-
ture faults and input voltage droops below the UVLO
threshold will cause an immediate OC output.
To limit the input voltage drop during momentary output
short-circuit conditions, connect a capacitor from IN to
GND. A 1µF ceramic capacitor is adequate for most
applications; however, higher capacitor values further
reduce the voltage drop at the input (Figure 2).
Connect a 0.1µF capacitor from OUT to GND. This
capacitor helps to prevent inductive parasitics from
pulling OUT negative during turn-off.
Figure 2. Typical Application Circuit
OVERCURRENT
* USB SPECIFICATIONS REQUIRE
INPUT
1μF
A HIGHER VALUE CAPACITOR.
OUTPUT
ON
1A Current-Limited Switch for 2 USB Ports
OFF
100kΩ
Applications Information
_______________________________________________________________________________________
IN
EN
OC
MAX1922
GND
Output Capacitor
Input Capacitor
OUT
0.1μF *
OUTPUT
Important: Optimize the switch response time to output
short-circuit conditions by keeping all traces as short
as possible to reduce the effect of undesirable parasitic
inductance. Place input and output capacitors as close
as possible to the device (no more than 5mm away). All
IN and OUT pins must be connected with short traces
to the power bus. Wide power-bus planes provide
superior heat dissipation through the MAX1922’s IN
and OUT pins. Under normal operating conditions, the
package can dissipate and channel heat away.
Calculate the maximum power dissipation as follows:
where I
R
When the output is short circuited, foldback-current lim-
iting activates and the voltage drop across the switch
equals the input supply voltage. The power dissipated
across the switch increases, as does the die tempera-
ture. If the fault condition is not removed, the thermal-
overload protection circuitry activates (see Thermal
Shutdown section). Wide power-bus planes connected
to IN and OUT and a ground plane in contact with the
device help dissipate additional heat.
A wide variety of devices (mice, keyboards, cameras,
and printers) can load the USB port. These devices
commonly connect to the port with cables, which can
add an inductive component to the load. This induc-
tance causes the output voltage at the USB port to ring
during a load step. The MAX1922 is capable of driving
inductive loads, but avoid exceeding the device’s
absolute maximum ratings. Usually the load inductance
is relatively small, and the MAX1922 input includes a
substantial bulk capacitance from an upstream regula-
tor as well as local bypass capacitors, limiting over-
shoot. If severe ringing occurs due to large load
inductance, clamp the MAX1922 output below 6V and
above -0.3V.
ON
is the on-resistance of the switch (125mΩ max).
LIMIT
is the preset current limit (2.1A max) and
Layout and Thermal Dissipation
P = (I
LIMIT
Driving Inductive Loads
)
2

R
ON
7