Rainbow Electronics MAX5929 - Manual (Page 13)

The MAX5927/MAX5929 turn off all channels if any of
the above conditions are not met. After a fault-latched
shutdown, cycle any of the ON_ inputs to unlatch and
restart all channels, depending on the corresponding
V
ON_ state.
Independent Mode
Connect MODE to GND to enter independent mode.
While in independent mode, the MAX5927/MAX5929
provide complete independent control for each chan-
nel. To turn on a given channel:
• At least one V IN_ must exceed V UVLO (2.45V) for the
UVLO to startup delay (37.5ms)
• The corresponding V IN_ must exceed V PWRRDY
(0.95V)
• The corresponding V ON_ must exceed V ON,TH
(0.875V)
The MAX5927/MAX5929 turn off the corresponding
channel if any of the above conditions are not met.
During a fault condition on a given channel only, the
affected channel is disabled. After a fault-latched shut-
down, recycle the corresponding ON_ inputs to unlatch
and restart only the corresponding channel.
Startup Period
R
TIM
sets the duration of the startup period from 0.4ms
(R TIM = 4k Ω) to 50ms (R
TIM = 500k Ω) (see the Setting
the Startup Period, R TIM section). The default startup
period is fixed at 9ms when TIM is floating. The startup
period begins after the turn-on conditions are met as
described in the Mode section, and the device is not
latched or in its autoretry delay (see the Latched and
Autoretry Fault Management section).
The MAX5927/MAX5929 limit the load current if an
overcurrent fault occurs during startup instead of com-
pletely turning off the external MOSFETs. The slow
comparator is disabled during the startup period and
the load current can be limited in two ways:
1) Slowly enhancing the MOSFETs by limiting the
MOSFET gate-charging current.
2) Limiting the voltage across the external current-
sense resistor.
During the startup period, the gate-drive current is limit-
ed to 100µA and decreases with the increase of the
gate voltage (see the Typical Operating Characteristics).
This allows the controller to slowly enhance the
MOSFETs. If the fast comparator detects an overcur-
rent, the MAX5927/MAX5929 regulate the gate voltage
to ensure that the voltage across the sense resistor
does not exceed V
SU,TH . This effectively regulates the
inrush current during startup.
Figure 6 shows the startup waveforms. STAT_ is assert-
ed immediately after the startup period if no fault condi-
tion is present.
VariableSpeed/BiLevel Fault Protection
VariableSpeed/BiLevel fault protection incorporates
comparators with different thresholds and response
times to monitor the load current (Figure 7). During the
startup period, protection is provided by limiting the
load current. Protection is provided in normal operation
(after the startup period has expired) by discharging
the MOSFET gates with a 3mA/50mA pulldown current
in response to a fault condition. After a fault, STAT_ is
deasserted, the MAX5929L stays latched off and the
MAX5929A automatically restart. Use the MAX5927
LATCH input to control whether the STAT_ outputs latch
off or Autoretry after a fault condition (see the Latched
and Autoretry Fault Management section).
MAX5927/MAX5929
Low-Voltage, Quad, Hot-Swap
Controllers/Power Sequencers
______________________________________________________________________________________________________ 13
Figure 4. Power-Sequencing Fault Turn-Off
ON1 = ON2 = ON3 = ON4
OVERCURRENT
FAULT
CONDITION
OUT1
OUT2
OUT3
OUT4
*THE OUT_ DISCHARGE RATE IS A RESULT OF NATURAL DECAY
OF THE LOAD RESISTANCE AND CAPACITANCE.
*
*
*
*