MAX4917BELT-T 查看數據表（PDF） - Maxim Integrated

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MAX4917BELT-T

100mA/200mA/300mA Current-Limit Switches with Low Shutdown Reverse Current

Maxim Integrated 

100mA/200mA/300mA Current-Limit Switches

with Low Shutdown Reverse Current

FIGURE 3a

tBLANK

tBLANK

LOAD

CURRENT

ON

SWITCH

STATUS

OFF

ON PIN

VOLTAGE

FLAG PIN

STATUS

FIGURE 3b

LOAD

CURRENT

ON

SWITCH

STATUS

OFF

IN PIN

VOLTAGE

FLAG PIN

STATUS

tBLANK

tBLANK

UVLO

Figure 3. MAX4914B/MAX4915B/MAX4917B Latchoff Fault

Blanking

Latchoff

(MAX4914B/MAX4915B/MAX4917B)

When the forward or reverse current-limit threshold is

exceeded, the tBLANK timer begins counting. The timer

resets if the overcurrent condition disappears before

tBLANK has elapsed. The switch is shut off if the over-

current condition continues up to the end of the blank-

ing time. Reset the switch by either toggling ON (Figure

3a) or cycling the input voltage below UVLO, typically

2V (Figure 3b).

Fault Blanking

All devices feature 14ms (min) fault blanking. Fault

blanking allows current-limit faults, including momentary

short-circuit faults that occur when hot-swapping a

capacitive load, and also ensures that no fault is issued

during power-up. When a load transient causes the

device to enter current limit, an internal counter starts. If

the load-transient fault persists beyond the fault-blank-

ing timeout, FLAG asserts low. Load-transient faults less

than tBLANK do not cause a FLAG output assertion. Only

current-limit faults are blanked.

A thermal fault and input voltage drops below the UVLO

threshold cause FLAG to assert immediately and not

wait for the blanking time.

Thermal Shutdown

The MAX4914B/MAX4915A/B/MAX4917A/B have a ther-

mal-shutdown feature to protect the devices from over-

heating. The switch turns off and FLAG goes low

immediately (no fault blanking) when the junction temper-

ature exceeds +150°C. The switch turns back on when

the device temperature drops approximately by 15°C.

Applications Information

Input Capacitor

To limit the input-voltage drop during momentary output

short-circuit conditions, connect a capacitor from IN to

GND. A 0.1µF ceramic capacitor is adequate for most

applications; however, higher capacitor values further

reduce the voltage drop at the input and are recom-

mended for lower voltage applications.

Output Capacitance

Connect a 0.1µF capacitor from OUT to GND. This

capacitor helps prevent inductive parasitics from

pulling OUT negative during turn-off, thus preventing

the devices from tripping erroneously. If the load

capacitance is too large, the current may not have

enough time to charge the capacitance and the device

assumes that there is a faulty load condition. The maxi-

mum capacitive load value that can be driven from

OUT is obtained by the following formula:

CMAX < IFWD_MIN

× tBLANK _MIN

VIN

Layout and Thermal Dissipation

To optimize the switch response time to output short-

circuit conditions, it is very important to keep all traces

as short as possible to reduce the effect of undesirable

parasitic inductance. Place input and output capacitors

as close as possible to the device (no more than 5mm).

IN and OUT pins must be connected with short traces

to the power bus.

During normal operation, the power dissipation is small

and the package temperature change is minimal. If the

output is continuously shorted to ground at the maximum

8 _______________________________________________________________________________________

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