MAX5949BESA+T Datasheet MAX5949AESA+, MAX5949AESA+T, MAX5949BESA+ | P13-P15

MAX5949A/MAX5949B

-48V Hot-Swap Controllers

with External R

SENSE

______________________________________________________________________________________ 13

PWRGD

GATE

∆V

GATE

-48V

R3 C2

MAX5949B

IN+

IN-

OUT+

OUT-

ON/OFF

ACTIVE-HIGH

ENABLE MODULE

DRAIN

GATESENSEV

*DIODES INC. SMAT70A.

-48V RTN

(SHORT PIN)

Figure 13. Active-High Enable Module

PWRGD

GATE

∆V

GATE

-48V

R3 C2

MAX5949A

IN+

IN-

OUT+

OUT-

ON/OFF

ACTIVE-LOW

ENABLE MODULE

DRAIN

GATESENSEV

*DIODES INC. SMAT70A.

-48V RTN

(SHORT PIN)

Figure 14. Active-Low Enable Module

MAX5949A/MAX5949B

When the DRAIN voltage of the MAX5949A is high with

respect to V

or the GATE voltage is low, the internal

pulldown MOSFET Q2 is off and the PWRGD pin is in a

high-impedance state (Figure 14). The PWRGD pin is

pulled high by the module’s internal pullup current

source, turning the module off. When the DRAIN volt-

age drops below V

and the GATE voltage is greater

than ∆V

GATE

- V

, Q2 turns on and the PWRGD pin

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 15) (see the

Component Selection Procedure

section).

When the DRAIN voltage of the MAX5949B is high with

respect to V

(Figure 13) or the GATE voltage is low, the

internal MOSFET Q3 is turned off so that I1 and the inter-

nal MOSFET Q2 clamp the PWRGD pin to the DRAIN pin.

MOSFET Q2 sinks the module’s pullup current, and the

module turns off.

When the DRAIN voltage drops below V

and the

GATE voltage is greater than ∆V

GATE

- V

, MOSFET

Q3 turns on, shorting I1 to V

and turning Q2 off. The

pullup current in the module pulls the PWRGD pin high,

enabling the module.

GATE Pin Voltage Regulation

The GATE pin goes high when the following startup con-

ditions are met: the UV pin is high, the OV pin is low, the

supply voltage is above V

UVLOH

, and (V

SENSE

- V

) is

less than 50mV. The gate is pulled up with a 45µA current

source and is regulated at 13.5V above V

. The

MAX5949A/MAX5949B include an internal clamp that

ensures the GATE voltage of the external MOSFET never

exceeds 18V. During a fast-rising V

, the clamp also

keeps the GATE and SENSE potentials as close as possi-

ble to prevent the FET from accidentally turning on. When

a fault condition is detected, the GATE pin is pulled low

with a 50mA current.

Applications Information

Sense Resistor

The circuit-breaker current-limit threshold is set to 50mV

(typically). Select a sense resistor that causes a drop

equal to or above the current-limit threshold at a current

level above the maximum normal operating current.

Typically, set the overload current to 1.5 to 2.0 times the

nominal load current plus the load-capacitance charging

current during startup. Choose the sense-resistor power

rating to be greater than (V

)

/ R

SENSE

-48V Hot-Swap Controllers

with External R

SENSE

14 ______________________________________________________________________________________

SENSE

GATE DRAIN

PWRGD

MAX5949A

-48V RTN

-48V

549kΩ

6.49kΩ

10kΩ

0.02Ω

1kΩ

10Ω

C1**

470nF

25V

IRF530

15nF

100V

-48V RTN

(SHORT PIN)

100µF

100V

*DIODES INC. SMAT70A.

**OPTIONAL.

PWRGD

MOC207

R7**

51kΩ

Figure 15. Using PWRGD to Drive an Optoisolator

Component Selection Procedure

• Determine load capacitance:

= C2 + C3 + module input capacitance

• Determine load current, I

LOAD

• Select circuit-breaker current; for example:

= 2 x I

LOAD

• Calculate R

SENSE

Realize that I

varies ±20% due to trip-voltage

tolerance.

• Set allowable inrush current:

• Determine value of C2:

• Calculate value of C1:

• Determine value of R3:

• Set R2 = 10Ω.

• If an optocoupler is utilized as in Figure 15, deter-

mine the LED series resistor:

Although the suggested optocoupler is not specified for

operation below 5mA, its performance is adequate for

36V temporary low-line voltage where LED current

would then be ≈2.2mA to 3.7mA. If R7 is set as high as

51kΩ, optocoupler operation should be verified over

the expected temperature and input voltage range to

ensure suitable operation when LED current ≈0.9mA for

48V input and ≈0.7mA for 36V input.

If input transients are expected to momentarily raise the

input voltage to >100V, select an input transient-volt-

age-suppression diode (TVS) to limit maximum voltage

on the MAX5949 to less than 100V. A suitable device is

the Diodes Inc. SMAT70A telecom-specific TVS.

Select Q1 to meet supply voltage, load current, efficien-

cy, and Q1 package power-dissipation requirements:

DSS

≥ 100V

D(ON)

≥ 3x I

LOAD

DPAK, D

PAK, or TO-220AB

The lowest practical R

DS(ON)

, within budget constraints

and with values from 14mΩ to 540mΩ, are available at

100V breakdown.

Ensure that the temperature rise of Q1 junction is not

excessive at normal load current for the package select-

ed. Ensure that I

current during voltage transients

does not exceed allowable transient-safe operating-area

limitations. This is determined from the SOA and tran-

sient-thermal-resistance curves in the Q1 manufacturer’s

data sheet.

Example 1:

LOAD

= 2.5A, efficiency = 98%, then V

= 0.96V is

acceptable, or R

DS(ON)

≤ 384mΩ at operating temper-

ature is acceptable. An IRL520NS 100V NMOS with

DS(ON)

≤ 180mΩ and I

D(ON)

= 10A is available in

PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS

with R

DS(ON)

≤ 25mΩ and I

D(ON)

= 40A is available in

DPAK, but may be more costly because of a larger die

size.)

Using the IRL520NS, V

≤ 0.625V even at +80°C so

efficiency ≥ 98.6% at 80°C. P

≤ 1.56W and junction

temperature rise above case temperature would be 5°C

due to the package θ

= 3.1°C/W thermal resistance.

Of course, using the SUD40N10-25 would yield an effi-

ciency greater than 99.8% to compensate for the

increased cost.

mA I mA

IN NOMINAL

LED

()

≤≤

−

typically k3

150

1≤

( )Ω

CCCx

IN MAX GS TH

GS TH

12=+

⎛

⎝

⎜

⎞

⎠

⎟

−

()

() ()

()

AxC

INRUSH

Ior

II xI

INRUSH

SENSE

LOAD

INRUSH LOAD CB MIN

≤

+≤

−08

()

SENSE

MAX5949A/MAX5949B

-48V Hot-Swap Controllers

with External R

SENSE

______________________________________________________________________________________ 15

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18

MAX5949BESA+T

Mfr. #:

Buy MAX5949BESA+T

Manufacturer:

Maxim Integrated

Description:

Hot Swap Voltage Controllers 48V- Hot-Swap Controlle

Lifecycle:

New from this manufacturer.

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MAX5949BESA+T

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