MAX5920AESA Maxim Integrated Products, MAX5920AESA Datasheet - Page 9

• Manufacturer Part Number: MAX5920AESA
• Description: Hot Swap & Power Distribution
• Manufacturer: Maxim Integrated Products

Specifications of MAX5920AESA

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Figure 6a shows a typical hot-swap circuit for -48V sys-
tems. When the circuit board first makes contact with
the backplane, the DRAIN to GATE capacitance (C
of Q1 pulls up the GATE voltage to roughly IV
C
ic clamp between GATE and V
source voltage of Q1 low during hot insertion,
preventing Q1 from passing an uncontrolled current to
the load. For most applications, the internal clamp
between GATE and V
eliminates the need for an external gate-to-source
capacitor. Resistor R3 limits the current into the clamp
circuitry during card insertion.
The MAX5920A/MAX5920B can reside either on the
backplane or the removable circuit board (Figure 6a).
Power is delivered to the load by placing an external
N-channel MOSFET pass transistor in the power-supply
path.
After the circuit board is inserted into the backplane
and the supply voltage at V
undervoltage and overvoltage tolerance, the
MAX5920A/MAX5920B turn on Q1. The MAX5920A/
MAX5920B gradually turn on the external MOSFET by
charging the gate of Q1 with a 45µA current source.
Figure 6a. Inrush Control Circuitry
gd
+ C
gs
I. The MAX5920_ features an internal dynam-
-48V RTN
*DIODES INC. SMAT70A.
**OPTIONAL.
-48V
_______________________________________________________________________________________
*
(SHORT PIN)
EE
-48V RTN
10nF
of the MAX5920A/MAX5920B
Power-Supply Ramping
EE
6.49kΩ
is stable and within the
549kΩ
EE
10kΩ
1%
1%
1%
R4
R5
R6
to keep the gate-to-
Board Insertion
UV
OV
V
EE
EE
0.02Ω
5%
R1
x C
SENSE
gd
gd
-48V Hot-Swap Controller
)
/
MAX5920B
C1**
470nF
25V
V
Capacitor C2 provides a feedback signal to accurately
limit the inrush current. The inrush current can be
calculated:
where C
I
Figure 6b shows the inrush current waveform. The cur-
rent through C2 controls the GATE voltage. At the end
of the DRAIN ramp, the GATE voltage is charged to its
final value. The GATE-to-SENSE clamp limits the maxi-
mum V
If the circuit card is removed from the backplane, the volt-
age at the UV pin falls below the UVLO detect threshold,
and the MAX5920_ turns off the external MOSFET.
The MAX5920_ provides current-limiting and circuit-
breaker features that protect against excessive load cur-
rent and short-circuit conditions. The load current is
monitored by sensing the voltage across an external
sense resistor connected between V
DD
PU
IRF530
GATE
with External R
Q1
is the MAX5920_ gate pullup current.
R2
10Ω
5%
GS
1kΩ
5%
R3
L
to about 18V under any condition.
is the total load capacitance, C3 + C4, and
15nF
100V
C2
PWRGD
DRAIN
I
INRUSH
Current Limit and Electronic
C3
0.1µF
100V
= I
PU
C4
100µF
100V
x C
L
V
V
EE
/ C2
IN+
IN-
Circuit Breaker
Board Removal
VI-J3D-CY
GATE IN
VICOR
and SENSE.
SENSE
9