LTC4230IGN datasheet(15/36 Pages) LINER

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LTC4230

4230f

Ensuring a proper start-up sequence is also dependent on

selecting the most appropriate value for CTIMER for the

application. Long timing periods affect overall system

start-up times. A timing period set too short and the

system may never start up. A good starting point is to set

CTIMER = 1µF and then adjust its value accordingly for the

application.

OPERATING SEQUENCE

Power-Up, Start-Up Check and Plug-In Timing Cycle

The sequence of operations for the LTC4230 is illustrated

in the timing diagram of Figure 5. When a PC board is first

inserted into a live backplane, the LTC4230 first performs

4 5

FIRST TIMING CYCLE

µA PULL-UP

4230 F05

NORMAL MODE

SECOND TIMING

CYCLE

CHECK FOR FILTER LOW (< VREF)

CHECK FOR FAULT HIGH (> VREF + 50mV)

CHECK FOR GATE

n < 0.2V

FAST COMPARATOR

ARMED

IF ON IS LOW AND

VFBn < 1.234V,

RESET 1, RESET 2 AND RESET 3

PULL LOW, RESPECTIVELY

TIMER

GATE

VOUTn

RESET 1

RESET 2,

RESET 3

µA PULL-UP

200

µA PULL-DOWN

SLOW COMPARATOR ARMED

POWER GOOD

(VFBn > 1.237V)

POWER BAD

(VFBn < 1.234V)

200

µA PULL-DOWN

Figure 5. Normal Power-Up Sequence

Table 1. tTIMER vs CTIMER

CTIMER

tTIMER

0.1

µF

6.2ms

0.22

µF

13.6ms

0.33

µF

20.4ms

0.47

µF

29ms

0.68

µF

42ms

0.82

µF

50.6ms

µF

61.7ms

2.2

µF

136ms

3.3

µF

204ms

4.7

µF

290ms

6.8

µF

420ms

8.2

µF

506ms

µF

617ms

APPLICATIO S I FOR ATIO

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