Positive High-Voltage, Hot-Swap Controllers

_______________________________________________________________________________________

9

Detailed Description

The MAX5933_ and MAX5947_ are fully integrated hot-

swap controllers for positive supply rails. The devices

allow for the safe insertion and removal of circuit cards

into live backplanes without causing glitches on the

backplane power-supply rail. During startup, the

MAX5933_ and MAX5947_ act as current regulators

using an external sense resistor and a MOSFET to limit

the amount of current drawn by the load.

The MAX5933_ operate from a +33V to +80V supply

voltage range and have a default undervoltage lockout

(UVLO) set to +31V. The MAX5947_ operate from a

+9V to +80V supply voltage range and have a default

UVLO set to +8.3V. The UVLO threshold is adjustable

GND (see Figure 5).

The MAX5933_ and MAX5947_ monitor the input volt-

age, the output voltage, the output current, and the die

temperature. These devices feature power-good outputs

(PWRGD/PWRGD) to indicate the status of the output

voltage by monitoring the voltage at FB (see the Power-

Good Detection section).

As shown in Figure 5, a sense resistor is connected

the voltage at FB

≥ 0.5V. The current-limit threshold

FB decreases from 0.5V to 0V.

An undervoltage fault is detected when ON goes below

goes low as a result to turn off the MOSFET. ON must

MOSFET again.

R6

1k

Ω

5%

C1

10nF

D1

CMPZ5248B

Q1

IRF530

R5

10

Ω

5%

0.025

Ω

R3

59k

Ω

1%

R4

3.57k

Ω

1%

R7

24k

Ω

5%

R2

3.4k

Ω

1%

R1

49.9k

Ω

1%

C2

0.68

µF

MAX5933A

PWRGD

GND

24V

TIMER

ON

PWRGD

FB

GND

SENSE

GATE

5

1

3

2

4

87

6

0.1

µF

Figure 5. Application Circuit