LTC4210-2CS6#TRM【PDF 15/20 页】IC CONTROLLER HOT SWAP TSOT23-6

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Sheet目录41

11页 12页 13页 14页 [15页]16页 17页 18页 19页

LTC4210-1/LTC4210-2

421012f

Normal Mode/External Timer Control

Whenever the TIMER pin voltage drops below the COMP1

threshold, but is not in reset mode, the TIMER enters

normal (100礎 source) mode with an equivalent 7k resis-

tive pull-down. Table 1 shows the relationship of t

INITIAL

CBDELAY

, t

COOLOFF

vs C

TIMER

If the TIMER pin is pulled beyond the COMP2 threshold,

the GATE pin is pulled to ground immediately. This allows

the TIMER pin to be used for overvoltage detection, see

Figure 11.

Externally forcing the TIMER pin below the COMP1 thresh-

old will reset the TIMER to normal mode. During overvolt-

age detection, the TIMERs 100礎 pull-down current will

continue to be on if (V

SENSE) voltage is below 50mV.

If the (V

SENSE) voltage exceeds 50mV during the

overvoltage detection, the TIMER current will be the same

as described for latched-off or autoretry mode. See the

section OVERVOLTAGE DETECTION USING TIMER PIN

for details of the application.

Power-Off Cycle

The system can be reset by toggling the ON pin low for

more than 30祍 as shown at time point 7 of Figure 3. The

GATE pin is pulled to ground. The TIMER capacitor is also

discharged to ground. C

LOAD

discharges through the load.

Alternatively, the TIMER pin can be externally driven above

the COMP2 threshold to turn off the GATE pin.

POWER MOSFET SELECTION

Power MOSFETs can be classified by R

DSON

at V

gate

drive ratings of 10V, 4.5V, 2.5V and 1.8V. Use the typical

curves VGATE vs Supply Voltage and VGATE vs Tem-

perature to determine whether the gate drive voltage is

adequate for the selected MOSFET at the operating volt-

age.

In addition, the selected MOSFET should fulfill two V

criteria:

1. Positive V

absolute maximum rating > LTC4210

maximum V

GATE

, and

2. Negative V

absolute maximum rating > supply

voltage. The gate of the MOSFET can discharge faster

than V

OUT

when shutting down the MOSFET with a large

LOAD

If one of the conditions cannot be met, an external Zener

clamp shown on Figure 10a or Figure 10b can be used. The

selection of R

should be within the allowed LTC4210

package dissipation when discharging V

OUT

via the Zener

clamp.

APPLICATIO S I FOR ATIO

Table 1. t

INITIAL

, t

CBDELAY

, t

COOLOFF

vs C

TIMER

(?/SPAN>F)

INITIAL

(ms)

CBDELAY

(ms)

COOLOFF

(ms)

0.033

9.0

0.7

18.2

0.047

12.8

25.9

0.068

18.6

1.5

37.4

0.082

22.4

1.8

45.1

0.1

27.3

2.2

0.22

60.0

4.8

121

0.33

90.1

7.2

181.5

0.47

128.3

10.2

258.5

0.68

185.6

14.7

374

0.82

223.8

17.8

451

272.9

21.7

550

2.2

600.5

47.7

1210

3.3

900.7

71.5

1815

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