LTC4230IGN datasheet(28/36 Pages) LINER

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LTC4230

4230f

APPLICATIO S I FOR ATIO

AUTORETRY AFTER A FAULT

To configure the LTC4230 to automatically retry after a

fault condition, the FAULT (which has an internal 2

µA pull-

up current source) and ON pins can be connected to-

gether, as shown in Figure 18. In this case, the autoretry

circuitry will attempt to restart the LTC4230 with an 7%

duty cycle, as shown in the timing diagram of Figure 19. To

prevent overheating the external MOSFET and other com-

ponents during the autoretry sequence, adding a capacitor

(CAUTO) to the circuit introduces a delay at the ON pin that

adjusts the autoretry duty cycle. Equation 14 gives the

autoretry duty cycle, modified by the external time con-

stant CAUTO:

Autoretry Duty Cycle

TIMER

OFF

TIMER

14 5

100

.•

•% (14)

where tTIMER = LTC4230 system time constant (see TIMER

function) and

OFF

AUTO

•.

1 314

For the values shown, the external delay equals 65.7ms

and the autoretry duty cycle drops from 7% to 4%.

To increase the RC delay, the user may either increase

CAUTO or RAUTO.

OVERVOLTAGE TRANSIENT PROTECTION

Good engineering practice calls for bypassing the supply

rail of any analog circuit. Bypass capacitors are often

placed at the supply connection of every active device, in

addition to one or more large value bulk bypass capacitors

per supply rail. If power is connected abruptly, the large

bypass capacitors slow the rate of rise of the supply

voltage and heavily damp any parasitic resonance of lead

or PC track inductance working against the supply bypass

capacitors.

CHECK FOR

TIMER < 0.3V

FIRST TIMING CYCLE

4230 F19

SECOND TIMING CYCLE

DISCHARGING MODE

NORMAL MODE

CHECK FOR FILTER LOW (< VREF)

CHECK FOR FAULT HIGH (> VREF + 50mV)

CHECK FOR GATE

n < 0.25V

FAST COMPARATOR

ARMED

SLOW COMPARATOR

ARMED

ONCE VFILTER > 1.26V, CIRCUIT BREAKER TRIPS,

ALL GATE

n PINS PULL LOW IMMEDIATELY

µA PULL-UP

1.6

µA PULL-DOWN

µA PULL-UP

VFILTER > 1.26V

VREF

µA PULL-DOWN

LOAD CURRENT < 150mV/RSENSEn

µA PULL-UP

ON/

TIMER

GATE

VOUTn

ILOADn

FILTER

FAULT

GATE

VOUTn

VSENSEn = 50mV

REGULATED

LOAD

CURRENT

Figure 19. Autoretry Timing

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