MAX5934 MAXIM [Maxim Integrated Products], MAX5934 Datasheet - Page 10

• Manufacturer Part Number: MAX5934
• Description: Positive High-Voltage, Hot-Swap Controllers with Selectable Fault Management and Status Polarity
• Manufacturer: MAXIM [Maxim Integrated Products]

Positive High-Voltage, Hot-Swap Controllers with
Selectable Fault Management and Status Polarity
where:
V
at FB1 = 0V and increases to 47mV as the voltage at
FB1 increases to 0.5V and beyond (see Figure 6).
Thus, the current limit is low at a low output voltage,
and increases as the output voltage reaches its final
value. This gradually increases the limiting load current
at startup and creates a foldback current limit under
overload or short-circuit conditions. See Figure 5 for
FB1 and R
During power-up, the MAX5934/MAX5934A gradually
turn on the external n-channel MOSFETs. The
MAX5934/MAX5934A monitor and provide current-limit
protection to the load at all times. The current limit is
programmable using an external current-sense resistor
connected from V
MAX5934A feature current-limit foldback and duty-cycle
limit to ensure robust operation during load-fault and
short-circuit conditions (see the Detailed Description
and Overcurrent Protection sections).
Connect an external capacitor from TIMER to ground to
set the maximum overcurrent timeout limit. When the volt-
age at TIMER reaches 1.233V, GATE goes low and the
75µA pullup current turns off (see the Functional
Diagram). As a result, a preset pulldown current
(I
fault latch, these two conditions must be met:
10
Figure 6. Current-Limit Sense Voltage vs. Feedback Voltage
TIMERON
SENSETRIP
V
CC
- V
______________________________________________________________________________________
SENSE
47mV
12mV
) discharges the capacitor. To reset the internal
0V
SENSE
varies from a low of 12mV when the voltage
V
SENSETRIP
I
LOAD
connections.
CC
=
to SENSE. The MAX5934/
V
= V
SENSETRIP
R
SENSE
IN
0.5V
- V
SENSE
Power-Up Mode
TIMER
V
FB
1) TIMER’s voltage goes below 0.5V
2) ON goes low
When the current limit is not active, TIMER goes low by
the I
becomes active, the I
connected to TIMER and the voltage rises with a slope
of 75µA/C
active. A capacitor from TIMER to GND (C
the desired current-limit timeout:
GATE provides a high-side gate drive for the external
n-channel MOSFET. An internal charge-pump circuit
guarantees at least 10V of gate drive for supply voltages
higher than 20V (MAX5934A) and a 4.5V gate drive for
supply voltages between 10.8V and 20V (MAX5934A)
(for the MAX5934, see the Electrical Characteristics
table). Connect an external capacitor from GATE to
ground to set the rising slope of the voltage at GATE.
The voltage at GATE is adjusted to maintain a constant
voltage across R
while the TIMER capacitor starts to charge. When the
voltage at TIMER exceeds 1.233V, the voltage at GATE
goes low.
The MAX5934/MAX5934A monitor voltages at ON, V
and TIMER. GATE is pulled to GND whenever ON goes
low, or the V
UVLO threshold, or TIMER increases above the 1.233V
threshold.
The Gate Drive vs. Supply Voltage graph in the Typical
Operating Characteristics illustrates that GATE clamps
to a maximum of 18V above the input voltage. The
MAX5934 minimum gate-drive voltage is 10V at a mini-
mum input-supply voltage of 33V. The MAX5934A mini-
mum gate-drive voltage is 4.5V at a minimum supply of
10.8V. Therefore, a logic-level MOSFET must be used if
the input supply is below 20V.
The MAX5934/MAX5934A feature either latched-off or
autoretry fault management configurable by the
LATCH/RETRY input. To select automatic restart after a
circuit-breaker fault, drive LATCH/RETRY high (above
V
LRIH
TIMERON
) or leave it floating (see Figure 5).
Fault Management ( LATCH /RETRY)
TIMER
T
LIMIT
CC
current source. After the current limit
SENSE
supply voltage decreases below the
as long as the current limit remains
= (C
TIMEROFF
TIMER
when the current limit is reached
/ 75µA) x 1.233V
pullup current source is
Gate Voltage
TIMER
GATE
) sets
CC
,