MAX5948BESA+T【PDF 13/18 页】IC CNTRLR HOT SWAP 8-SOIC

A separate resistor-divider must be used for the over-

voltage lockout setting. The supply overvoltage lockout

threshold is:

where V

OVH

is typically 1.223V.

Using R1 = 562k&, R2 = 16.9k&, R3 = 1.62M&, R4 =

506k&, R5 = 8.87k&, and the typical value of V

GATE

=

13.5V results in the following thresholds:

V

UV,HL

= 37.6V

V

UV,LH

= 43V

(with hysteresis now increased to 5.4V), and V

OV

= 71V

(with 1.2V hysteresis).

PWRGD/PWRGD Output

The PWRGD (PWRGD) output can be used directly to

enable a power module after hot insertion. The

MAX5948A (PWRGD) can be used to enable modules

with an active-low enable input (Figure 13), while the

MAX5948B (PWRGD) is used to enable modules with

an active-high enable input (Figure 12).

The PWRGD signal is referenced to the DRAIN termi-

nal, which is the negative supply of the power module.

The PWRGD signal is referenced to V

EE

.

When the DRAIN voltage of the MAX5948A is high with

respect to V

EE

, the internal pulldown MOSFET Q2 is off

and the PWRGD pin is in a high-impedance state

(Figure 13). PWRGD is pulled high by the modules

internal pullup current source, turning the module off.

When the DRAIN voltage drops below V

PG

, Q2 turns on

and PWRGD pulls low, enabling the module.

The PWRGD signal can also be used to turn on an LED

or optoisolator to indicate that the power is good

(Figure 13) (see the Component Selection Procedure

section).

V V

R R

R

OV

OVH

=

+

?/DIV>

4 5

5

-48V Hot-Swap Controllers

with External R

SENSE

______________________________________________________________________________________ 13

PWRGD

I1

V

EE

V

PG

-48V

R1

R2

C1

Q1

R3

C2

MAX5948B

V

IN+

V

IN-

C4

Q2

Q3

V

OUT+

V

OUT-

ON/OFF

VICOR

VI-J3D-CY

DRAIN

GATE

SENSE

V

EE

V

DD

R4

R5

R6

*

*DIODES INC. SMAT70A.

-48V RTN

(SHORT PIN)

UV

OV

Figure 12. Active-High Enable Module

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