MAX14721 datasheet(13/20 Pages) MAXIM

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accepting signals up to 60V. EN is a low-voltage input,

accepting a maximum voltage of 5V. In case of a fault

condition, toggling HVEN or EN resets the fault. The

enable inputs control the state of the switch based on the

truth table (Table 1).

Input Debounce

The MAX14721–MAX14723 feature a built-in input

debounce time (tDEB). 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 VUVLO present on IN,

the enable pins toggle to the on state, the switch turns on

after tDEB. In cases where the voltage at IN falls below

VUVLO before tDEB has passed, the switch remains

off (Figure 2). If the voltage at OUT is already above

VUVLO_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 VUVLO_OUT.

Current-Limit Type Select

The MAX14721–MAX14723 feature three selectable

current-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 successfully powered on and tSTO has expired,

the device senses the condition of CLTS1 and CLTS2.

The condition of CLTS1 and CLTS2 sets the current-limit

mode type according to Table 2. CLTS1,2 are internally

pulled up to an internal 5V supply. Therefore, the device is

in continuous current-limit mode when CLTS1 and CLTS2

are open. To set CLTS_ state to low, connect a 10kΩ

resistor or below to ground.

In addition to the selectable current-limiting modes, the

device has a protection feature against a severe over

load condition. If the output current exceeds 2 times the

set current limit, the device will turn off the internal nFET

and external pFET immediately and will attempt to restart

to allow the overcurrent to last for tBLANK time. The OFF

duration depends on fault condition occurred after the

FETs turn off, with the shortest duration of 420µs (tON_FET)

if there is no fault. In Latchoff mode, the device will latch

off if the overcurrent fault last longer than tBLANK.

Autoretry Mode (Figure 3)

In autoretry current-limit mode, when current through the

device reaches the threshold, the tBLANK timer begins

counting. The FLAG output asserts low when the voltage

drop across the switch rises above VFA. If the overcurrent

condition is present for tBLANK, the switch is turned off.

The timer resets if the overcurrent condition disappears

before tBLANK has elapsed. A retry time delay (tRETRY)

starts immediately once tBLANK has elapsed. During the

retry time, the switch remains off and, once tRETRY 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 tBLANK time, the supply current is held at the

currentlimit.WhentheswitchisoffduringtRETRYtime,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.

BLANK

STI

LOAD

LIM

BLANK

RETRY

STI







where K is the multiplication factor of the initial current

limit (1x, 1.5x or 2x). With a 24ms (typ) tBLANK, 24ms

tSTI, K = 1 and 720ms (typ) tRETRY, the duty cycle is

3.1%, resulting in 97% power saving as compared to the

switch being on the entire time.

Latchoff Mode (Figure 4)

In latchoff current-limit mode, when current through the

device reaches the threshold, the tBLANK timer begins

counting. The FLAG asserts when the voltage drop across

the switch rises above VFA. The timer resets if the overcurrent

condition disappears before tBLANK has elapsed. The

switch turns off if the overcurrent condition remains for the

blanking time. The switch remains off until the control logic

(EN or HVEN) is toggled or the input voltage is cycled.

Table 1. Enable Inputs

HVEN

SWITCH STATUS

OFF

Table 2. Current-Limit Type Select

CLTS2

CLTS1

CURRENT-LIMIT TYPE

LATCHOFF MODE

AUTORETRY MODE

CONTINUOUS MODE

MAX14721/

MAX14722/

MAX14723

High-Accuracy, Adjustable Power Limiter

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