MAX14575A Datasheet, PDF (8/11 Pages) Maxim Integrated Products – 250mA to 2.5A Adjustable Current-Limit Switches

MAX14575A/MAX14575AL/
MAX14575B/MAX14575C
250mA to 2.5A Adjustable Current-Limit Switches
Functional Diagram
REVERSE-CURRENT
PROTECTION
IN
OUT
THERMAL
SHUTDOWN
MAX14575A
MAX14575AL
MAX14575B
MAX14575C
BUFFER
CONTROL
LOGIC
FLAG
TIMING
CIRCUITRY
EN(EN)*
BANDGAP
CURRENT
REFERENCE
LIMIT
BUFFER
SETI
*PARENTHESES ARE FOR THE MAX14575AL ONLY
Detailed Description
The MAX14575A/MAX14575AL/MAX14575B/MAX14575C
programmable current-limit switches operate from +2.3V
to +5.5V and provide internal current limiting adjust-
able from 250mA to 2.5A. These devices feature a fixed
blanking time and a FLAG output that notifies the proces-
sor when a fault condition is present.
Programmable Current-Limit Threshold
A resistor from SETI to GND sets the current-limit thresh-
old for the switch (see the Setting the Current-Limit
Threshold section). If the output current is limited at the
current threshold value for a time equal to or longer than
tBLANK with VIN - VOUT higher than the FLAG assertion
drop voltage threshold (VFA.), then the FLAG asserts,
and the MAX14575A/MAX14575AL enter the autoretry
mode, the MAX14575B latches off the switch, and the
MAX14575C enters the continuous current-limit mode.
Autoretry (MAX14575A/MAX14575AL)
When the forward current reaches the current thresh-
old, the tBLANK timer begins counting (Figure 2). FLAG
asserts if the overcurrent condition is present for tBLANK.
The timer resets if the overcurrent condition disappears
8  
before the blanking time (tBLANK) has elapsed. A retry
time delay (tRETRY) starts immediately after the blanking
time has elapsed and during that time, the switch latches
off. At the end of tRETRY, the switch turns on again. If the
fault still exists, the cycle repeats. If the fault has been
removed, the switch stays on. During this cycle, FLAG
stays low. In autoretry, if the die temperature exceeds
+160NC (typ) due to self-heating, the MAX14575A/
MAX14575AL go into thermal-shutdown mode until the
die temperature drops by approximately 20NC.
The autoretry feature saves system power in case of
an overcurrent or short-circuit condition. During tBLANK
time, when the switch is on, the supply current is held at
the current limit. During time tRETRY, when the switch is
off, the current through the switch is zero. Thus, the aver-
age output current is much less than the programmed
current limit. Calculate the average output current using
the following equation:
I_LO= _AD
I_LIM
×
t
t _BLANK
BLANK ^{+ t}RETRY
For example, if tBLANK = 15ms and tRETRY = 500ms, the
duty cycle is 3%, resulting in a 97% power savings over
the switch being on the entire time.
Maxim Integrated