max5938 Maxim Integrated Products, Inc., max5938 Datasheet - Page 12

• Manufacturer Part Number: max5938
• Description: Max5938 -48v Hot-swap Controller With Vin Step Immunity, No Rsense, And Overvoltage Protection
• Manufacturer: Maxim Integrated Products, Inc.

-48V Hot-Swap Controller with V
No R
In the MAX5938, the circuit-breaker and short-circuit
functions can be disabled, if desired, although this is
not recommended. (See Warning note in the PGOOD
Open-Drain Output section). This can be accomplished
by leaving CB_ADJ open. In this case, PGOOD asserts
1.26ms after GATE has ramped to 90% of full enhance-
ment, after which V
cuit-breaker and short-circuit faults being ignored.
The power-good output, PGOOD, is open drain and is
referenced to V
ramps below 74% of V
this occurs 1.26ms after the external MOSFET becomes
fully enhanced. PGOOD deasserts any time the part
enters fault management. PGOOD has a delayed
response to ON and OFF. The GATE will go to V
when OFF is brought below 1.25V (no time depen-
dence) while ON is brought below 1.125V for 1.5ms.
This turns off the power MOSFET and allows V
rise depending on the RC time constant of the load.
PGOOD, in this situation, deasserts when V
above V
whichever occurs first (see Figure 9b).
Since PGOOD is open drain, it requires an external
pullup resistor to GND. Due to this external pullup,
PGOOD does not follow positive V
it were driven by an active pullup. As a result, when
PGOOD is asserted high, an apparent negative glitch
appears at PGOOD during a positive V
negative glitch is a result of the RC time constant of the
external resistor and the PGOOD pin capacitance lag-
ging the V
nal logic. To minimize this negative transient, it may be
necessary to increase the pullup current and/or to add
a small amount of capacitance from PGOOD to GND to
compensate for the pin capacitance.
The PGOOD output logic polarity is selected using
POL_SEL input. For an active-high output, connect
POL_SEL to V
low output.
WARNING: When disabling the circuit-breaker and
short-circuit functions (CB_ADJ open), PGOOD asserts
1.26ms after the power MOSFET is fully enhanced inde-
pendent of V
and ON and OFF are pulled below their respective
thresholds, the GATE will be pulled to V
power MOSFET and disconnect the load. When the cir-
12
______________________________________________________________________________________
CB
IN
SENSE
step. It is not due to switching of the inter-
OUT
for more than 1.4ms or above V
EE
. Leave POL_SEL open for an active-
OUT
. Once the MOSFET is fully enhanced
Disabling Circuit-Breaker and
OUT
. It asserts and latches if V
PGOOD Open-Drain Output
CB
is ignored, resulting in the cir-
, and Overvoltage Protection
Short-Circuit Functions
, and with the built-in delay,
IN
steps as well as if
EE
IN
to turn off the
step. This
OUT
OUT
rises
OUT
SC
EE
to
,
cuit-breaker and short-circuit functions are disabled
and ON and OFF are cycled low, PGOOD is deassert-
ed. In summary, when CB_ADJ is open (once the MOS-
FET is fully enhanced), the MAX5938 ignores V
deasserts PGOOD only for an overvoltage fault, when
ON and OFF are cycled low or when the power to the
MAX5938 is fully recycled.
Figure 9. ON and OFF Timing Diagram
PGOOD
GATE
V
OFF
OUT
ON
OFF
ON
I
LP
IN
V
OFF_REF
V
V
ON_REF,F
OFF_REF
V
ON_REF,R
Step Immunity,
(a)
220ms
(b)
1.3ms
DETECTION TEST
LOAD-PROBE
BEGINS
OUT
and