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MAX4914B/MAX4915A/B/MAX4917A/B
Latchoff
(MAX4914B/MAX4915B/MAX4917B)
When the forward or reverse current-limit threshold is
exceeded, the tBLANK timer begins counting. The timer
resets if the overcurrent condition disappears before
tBLANK has elapsed. The switch is shut off if the over-
current condition continues up to the end of the blank-
ing time. Reset the switch by either toggling ON (Figure
3a) or cycling the input voltage below UVLO, typically
2V (Figure 3b).
Fault Blanking
All devices feature 14ms (min) fault blanking. Fault
blanking allows current-limit faults, including momentary
short-circuit faults that occur when hot-swapping a
capacitive load, and also ensures that no fault is issued
during power-up. When a load transient causes the
device to enter current limit, an internal counter starts. If
the load-transient fault persists beyond the fault-blank-
ing timeout,
FLAG asserts low. Load-transient faults less
than tBLANK do not cause a FLAG output assertion. Only
current-limit faults are blanked.
A thermal fault and input voltage drops below the UVLO
threshold cause
FLAG to assert immediately and not
wait for the blanking time.
Thermal Shutdown
The MAX4914B/MAX4915A/B/MAX4917A/B have a ther-
mal-shutdown feature to protect the devices from over-
heating. The switch turns off and
FLAG goes low
immediately (no fault blanking) when the junction temper-
ature exceeds +150°C. The switch turns back on when
the device temperature drops approximately by 15°C.
Applications Information
Input Capacitor
To limit the input-voltage drop during momentary output
short-circuit conditions, connect a capacitor from IN to
GND. A 0.1F ceramic capacitor is adequate for most
applications; however, higher capacitor values further
reduce the voltage drop at the input and are recom-
mended for lower voltage applications.
Output Capacitance
Connect a 0.1F capacitor from OUT to GND. This
capacitor helps prevent inductive parasitics from
pulling OUT negative during turn-off, thus preventing
the devices from tripping erroneously. If the load
capacitance is too large, the current may not have
enough time to charge the capacitance and the device
assumes that there is a faulty load condition. The maxi-
mum capacitive load value that can be driven from
OUT is obtained by the following formula:
Layout and Thermal Dissipation
To optimize the switch response time to output short-
circuit conditions, it is very important to keep 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).
IN and OUT pins must be connected with short traces
to the power bus.
During normal operation, the power dissipation is small
and the package temperature change is minimal. If the
output is continuously shorted to ground at the maximum
C
It
V
MAX
FWD MIN
BLANK MIN
IN
<
×
__
100mA/200mA/300mA Current-Limit Switches
with Low Shutdown Reverse Current
8
_______________________________________________________________________________________
LOAD
CURRENT
SWITCH
STATUS
ON PIN
VOLTAGE
tBLANK
OFF
ON
UVLO
LOAD
CURRENT
SWITCH
STATUS
IN PIN
VOLTAGE
OFF
ON
tBLANK
FLAG PIN
STATUS
FLAG PIN
STATUS
FIGURE 3a
FIGURE 3b
Figure 3. MAX4914B/MAX4915B/MAX4917B Latchoff Fault
Blanking