LTC4366 datasheet(11/22 Pages) AD

11 / 22 page

LTC4368

Rev. B

For more information www.analog.com

The external resistive divider allows the user to select

an input supply range that is compatible with the load

at VOUT. Furthermore, the UV and OV inputs have very

low leakage currents (typically < 1nA at 100°C), allow-

ing for large values in the external resistive divider. In

the application of Figure 4, the load is connected to the

supply only if VIN lies between 3.5V and 18V. In the event

that VIN goes above 18V or below 3.5V, the gate of the

external N-channel MOSFET is immediately discharged

with a 60mA current sink, thus isolating the load from

the supply.

Figure 5 shows the timing associated with the UV pin.

Once a UV fault propagates through the UV comparator

(tFAULT), the FAULT output is asserted low and a 60mA

current sink discharges the GATE pin. As VOUT falls, the

GATE pin tracks VOUT.

Figure 6 shows the timing associated with the OV pin.

Once an OV fault propagates through the OV comparator

(tFAULT), the FAULT output is asserted low and a 60mA

current sink discharges the GATE pin. As VOUT falls, the

GATE pin tracks VOUT.

APPLICATIONS INFORMATION

VIN

12V

UVTH = 3.5V

OVTH = 18V

4368 F04

DISCHARGE GATE

WITH 60mA SINK

LTC4368

COMPARATOR

1820k

0.5V

243k

59k

–

25mV

Figure 4. UV, OV Comparators Monitor 12V Supply

As VOUT ramps up from 0V, the absolute value of the GATE

voltage remains fixed until VOUT is greater than the lower

of (VIN – 1V) or 5V. Once VOUT crosses this threshold,

gate drive begins to increase up to a maximum of 13.1V.

The curves of Figure 3 were taken with a GATE load of

–1µA. If there were no DC load on GATE, the gate drive

for each VIN would be slightly higher.

Note that when VIN is at the lower end of the operating

range, the external N-channel MOSFET must be selected

with a correspondingly lower threshold voltage.

Overvoltage and Undervoltage Protection

The LTC4368 provides two accurate comparators to moni-

tor for overvoltage (OV) and undervoltage (UV) conditions

at VIN. If the input supply rises above the user adjust-

able OV threshold, the gates of the external MOSFETs

are quickly turned off, thus disconnecting the load from

the input. Similarly, if the input supply falls below the

user adjustable UV threshold, the gates of the external

MOSFETs are quickly turned off. Figure 4 shows a UV/OV

application for an input supply of 12V.

4368 F05

FAULT

GATE

tFAULT

tD(FAST)

VUV

VUV + VUVHYST

tD(ON)

EXTERNAL N-CHANNEL MOSFETS

TURN OFF

Figure 5. UV Timing (OV < (VOV – VOVHYST), SHDN > 1.2V)

4368 F06

tFAULT

tD(FAST)

VOV

VOV – VOVHYST

tD(ON)

EXTERNAL N-CHANNEL MOSFET

TURNS OFF

FAULT

GATE

Figure 6. OV Timing (UV > (VUV + VUVHYST), SHDN > 1.2V)

LTC4366 датащи(PDF) 11 Page - Analog Devices

LTC4366 датащи(HTML) 11 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

датащи скачать

ссылки URL