MAX4914B Maxim, MAX4914B Datasheet - Page 7

• Manufacturer Part Number: MAX4914B
• Description: The MAX4914B/MAX4915A/B/MAX4917A/B family of switches feature internal current limiting to prevent damage to host devices due to faulty load conditions
• Manufacturer: Maxim

drain output transistor and requires an external pullup
resistor from FLAG to IN. During shutdown (V
the pulldown on the FLAG output is released in order to
limit power dissipation. FLAG goes low when any of the
following conditions occur:
• The die temperature exceeds the thermal-shutdown
• The device is in current limit for more than the fault-
• V
For the MAX4915A/MAX4917A (autoretry versions),
FLAG stays low until the overcurrent condition is
removed (See Figure 2).
When the forward or reverse current-limit threshold is
exceeded, t
The timer resets if the overcurrent condition disappears
Table 1. MAX4914B/MAX4915A/B/MAX4917A/B Switch Truth Table
Figure 2. MAX4915A/MAX4917A Autoretry Fault-Blanking Diagram
temperature limit of +150°C.
blanking period.
High
High
High
Low
IN
ON
100mA/200mA/300mA Current-Limit Switches
is below the UVLO threshold.
Autoretry (MAX4915A/MAX4917A)
Undervoltage lockout
BLANK
Current limit
_______________________________________________________________________________________
Thermal
FAULT
timer begins counting (Figure 2).
X
with Low Shutdown Reverse Current
SWITCH
STATUS
STATUS
OFF
FLAG
ON
OFF
OFF
OFF immediately (t
OFF after t
ON during t
MAX4915A/MAX4917A (autoretry versions); cycle repeats
until fault is removed
t
BLANK
BLANK
BLANK
ON
t
RETRY
< V
period has elapsed
period, OFF during t
BLANK
IL
SWITCH ON/OFF
),
t
period does not apply)
BLANK
before t
is started immediately after t
during that time, the switch is latched off. At the end of
t
exists, the cycle is repeated. If the fault has been
removed, the switch stays on.
The autoretry feature saves system power in the case
of an overcurrent or short-circuit condition. During
t
the current limit. During t
the current through the switch is zero. Instead of
observing the full load current, the switch sees the
equivalent load current times duty cycle or I
I
t
cycle is 6%, which results in a 94% power savings over
the switch being on the entire time. The duty cycle is
consistent across the process and devices.
RETRY
BLANK
LOAD
BLANK
, the switch is turned on again. If the fault still
, when the switch is on, the supply current is at
RETRY
✕
BLANK
= 37ms and typical t
t
BLANK
t
period for the
BLANK
has elapsed. A retry time delay, t
/ (t
CURRENT
CONDITION
REMOVED
LIMIT
SHORT
BLANK
RETRY
+ t
RETRY
BLANK
SUPPLY CURRENT MODE
, when the switch is off,
(MAX4915A/MAX4917A)
RETRY
See the Autoretry
= 555ms, the duty
has elapsed, and
Shutdown
Shutdown
). With a typical
Latchoff
Latchoff
section
SUPPLY
RETRY
7
=
,