Datasheet

MAX4785–MAX4788
The switches with autoretry feature turn back on when
the device temperature drops approximately 15°C. The
switches with latchoff feature require ON cycling.
Applications Information
Input Capacitor
To limit the input voltage drop during momentary output
short-circuit conditions, connect a capacitor from IN to
GND. A 0.1µF 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 0.1µF capacitor from OUT to GND. This
capacitor helps prevent inductive parasitics from
pulling OUT negative during turn-off, thus preventing
the MAX4785–MAX4788 from tripping erroneously. If
the load capacitance is too large, then current may not
have enough time to charge the capacitance and the
device assumes that there is a faulty load condition.
The maximum 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 maxi-
mum supply voltage, the operation of the switches with
the autoretry option does not cause problems because
the total power dissipated during the short is scaled by
the duty cycle:
where V
IN
= 5.5V, I
OUT
= 240mA, t
BLANK
= 14ms, and
t
RETRY
= 98ms.
Attention must be given to the MAX4785 and MAX4787
where the latch-off condition must be manually reset by
toggling ON from high to low. If the latch-off time dura-
tion is not sufficiently high, it is possible for the device
to reach the thermal-shutdown threshold and never be
able to turn the device on until it cools down.
P
VI t
tt
mW
MAX
IN MAX OUT MAX BLANK
RETRY BLANK
=
××
+
=
__
161
C
It
V
MAX
FWD MIN BLANK MIN
IN
<
×
__
50mA/100mA Current-Limit Switches
8 _______________________________________________________________________________________
LOAD
CURRENT
SWITCH
STATUS
t
BLANK
t
BLANK
OFF
ON
ON PIN
VOLTAGE
(a)
(b)
UVLO
FLAG
PIN STATUS
LOAD
CURRENT
SWITCH
STATUS
OFF
ON
IN PIN
VOLTAGE
FLAG
PIN STATUS
t
BLANK
t
BLANK
Figure 3. MAX4785/MAX4787 Latch Off Fault Blanking
Selector Guide
PART
CURRENT
LIMIT (mA)
FLAG
FUNCTION
AUTO-
RETRY
MAX4785EXS
50 No No
MAX4785EXK
50 Yes No
MAX4786EXS
50 No Yes
MAX4787EXS
100 No No
MAX4787EXK
100 Yes No
MAX4788EXS
100 No Yes