LTC4151 datasheet(20/82 Pages) AD

20 / 82 page

LTC4284

Rev. B

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APPLICATIONS INFORMATION

For applications at very high voltages (>300V), a high

voltage MOSFET can be used. Figure 3 shows an appli-

cation circuit with a depletion mode N-channel MOSFET

that can withstand up to 1000V drain-to-source voltage.

In this case RZ is chosen according to

RZ ≤

VS(MIN)–VIN(MAX) – VGS

20µA

where VGS is the gate-to-source voltage of the MOSFET

(positive for an enhancement mode and negative for a

depletion mode transistor) . When using an enhancement

mode transistor, VZ voltage must be kept lower than its

absolute maximum of 16V:

VZ(MAX) = VIN(MAX) + VGS < 16V

In Figures 2b and 3, the voltage drop and power dissipa-

tion in the NPN or the MOSFET may be augmented by

the use of one or more resistors in series with the col-

lector or drain. If an external 12V supply is available on

the application board, it may be used to drive the VIN pin

directly as shown in Figure 4.

Turn-On Sequence

The following conditions must be satisfied before the

turn-on sequence is started. First the voltage at VIN must

exceed the undervoltage lockout level of 8.1V. Next the

internal supply INTVCC must cross its 4V undervoltage

lockout level. This generates a 1.3ms power-on-reset

delay. After the delay times out, the voltages at UVH, UVL

and OV must satisfy UVH > 2.048V, UVL > 1.833V and

OV < 1.406V to indicate that the input power is within the

acceptable range, and EN# must be pulled low. All the

above conditions must be satisfied throughout the dura-

tion of the startup debounce delay of 128ms. If any of the

above conditions is violated during the delay, the delay is

reset and restarted. After the delay expires, if the ON bit

in CONTROL_1 register 0x0A is high, the LTC4284 turns

on the MOSFETs. Otherwise, the MOSFET will be turned

Figure 2a. –48V/1200W Dual-Feed Hot Swap Controller with LTC4284 in Parallel Mode (Part One)

750

0.5m

RS1

0.5m

RS2

20k

10k

CE1

4.7nF

CE2

68nF

RE1

18.2k

RE2

1.13M

CUV

100nF

2N5401

100k

100A

10k

100k

CEN

1µF

R10

100k

HZS5C1

100A

10k

RRT

200k

RRB

5.11k

499k

2N5401

R11

5.62k

R12

20k

RTN A

UVH

UVL

–48V B

ADIN1-4

TMR

VEE

SENSE1–

SENSE1+

RAMP

SENSE2–

ADIO1-4

LTC4284

ADC–

SENSE2+

ADC+

DVDT = 0

THERM_TMR = 1

PWRGD_RESET_CNTRL = 1

ILIM = 0001

FB = 11

FB_DIS = 1

LPFB = 1

4284 F02a

EN#

UV = 32.4V

UV RELEASE AT 35.3V

OV = 74.5V

OV RELEASE AT 73.2V

VEE

LTC4371

RTN B

–48V A

LTC4355

1N4148

×2

RTNS

BACKPLANE PLUG-IN

CARD

MODE

VEE

4×

VOUTTH

VREF

VEE

RA1–

RA2–

RA1+

RA2+

BATTERY OPERATED

(SUBJECT TO –36V INPUT STEPS)

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