MAX14691 Datasheet, PDF (12/19 Pages) Maxim Integrated Products – High-Accuracy, Adjustable Power Limiter

MAX14691–MAX14693
High-Accuracy, Adjustable Power Limiter
Table 1. Enable Inputs
HVEN
EN
0
0
0
1
1
0
1
1
SWITCH STATUS
ON
ON
OFF
ON
Input Debounce
The devices feature a built-in input debounce time (t_DEB).
The debounce time is a delay between a POR event and
the switch being turned on. If the input voltage rises above
the UVLO threshold voltage or if, with a voltage greater
than V_UVLO present on IN, the enable pins toggle to the
on state, the switch turns on after t_DEB. In cases where
the voltage at IN falls below V_UVLO before t_DEB has
passed, the switch remains off (Figure 2). If the voltage
at OUT is already above V_{UVLO_OUT} when the device
is turned on through either enable pin or coming out of
OVLO, there is no debounce interval. This is due to the
device already being out of the POR condition with OUT
above V_{UVLO_OUT}.
Reverse-Current Blocking
The devices feature current-blocking functionality. To
enable the reverse-current blocking feature, pull RIPEN
high. With RIPEN high, if a reverse-current condition is
detected, the internal nFET and the external pFET are
turned off for 2.4ms. After this time, the switches are briefly
switched back on to determine whether the reverse cur-
rent is still present. Once the reverse-current condition has
been removed, the nFET and pFET are turned back on and
the dual-stage startup control mechanism, defined in the
Startup Control section above, is applied.
Current-Limit Type Select
The MAX14691–MAX14693 feature three selectable cur-
rent-limiting modes. During power-up, all devices default
to continuous mode and follow the procedure defined in
the Startup Control section. Once the part has been suc-
cessfully powered on and t_STO has expired, the device
Table 2. Current-Limit Type Select
CLTS2
0
0
1
1
CLTS1
0
1
0
1
CURRENT-LIMIT TYPE
LATCHOFF MODE
AUTORETRY MODE
CONTINUOUS MODE
CONTINUOUS USED
senses the condition of CLTS1 and CLTS2. The condition
of CLTS1 and CLTS2 sets the current-limit mode type
according to Table 2.
Autoretry Mode (Figure 3)
In autoretry current-limit mode, when current through the
device reaches the threshold, the t_BLANK timer begins
counting. The FLAG output asserts low when the voltage
drop across the switch rises above V_FA. If the overcurrent
condition is present for t_BLANK, the switch is turned off.
The timer resets if the overcurrent condition disappears
before t_BLANK has elapsed. A retry time delay (t_RETRY)
starts immediately once t_BLANK has elapsed. During the
retry time, the switch remains off and, once t_RETRY has
elapsed, the switch is turned back on. If the fault still
exists, the cycle is repeated and FLAG remains low. If the
fault has been removed, the switch stays on.
The autoretry feature reduces system power in case of
overcurrent or short-circuit conditions. When the switch is
on during t_BLANK time, the supply current is held at the cur-
rent limit. When the switch is off during t_RETRY time, there
is no current through the switch. Thus, the output current
is much less than the programmed current limit. Calculate
the average output current using the following equation:
I _LOAD
=
I_LIM

_t
t _BLANK + t _STI
BLANK ^{+ t} RETRY
×K
+t
STI



where K is the multiplication factor of the initial current
limit (1x, 1.5x or 2x). With a 24ms (typ) t_BLANK, 24ms
t_STI, K = 1 and 720ms (typ) t_RETRY, the duty cycle is
3.1%, resulting in 97% power saving when compared to
the switch being on the entire time.
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