max5938 Maxim Integrated Products, Inc., max5938 Datasheet - Page 18

• 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
Appendix B gives a more complete analysis and dis-
cussion of the step monitor function. It provides meth-
ods for the characterization of the load response to a
V
timing margins for a set of design parameters.
Due to the open-drain driver, PGOOD requires an exter-
nal pullup resistor to GND. This resistor should be
selected to minimize the current load while PGOOD is
low. The PGOOD output specification for V
1mA. As described in the Detailed Description, the
external pullup interferes with the ability of PGOOD to
follow positive V
active pullup. When PGOOD is asserted high, an appar-
ent negative glitch appears at PGOOD during a positive
V
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 load-probe test is a current test of the load that
avoids turning on the power MOSFET. The MAX5938
has an internal switch (Q1 in Figure 17) that pulls cur-
rent through the load and through an external current-
Figure 17. Load Probe Functional Diagram
18
IN
IN
ramp and graphical verification of the step monitor
step. To minimize this negative transient it may be
______________________________________________________________________________________
Selecting the PGOOD Pullup Resistor
SENSE
Setting the Test Current Level for
V
IN
IN
steps as well as if it were driven by an
, and Overvoltage Protection
GND
V
EE
Q1
200mV
Load-Probe Test
OL
R
MAX5938
ON
GATE
is 0.4V at
limiting resistor, R
pulsed on for up to 220ms (typ). Current is pulled
through the load, which should charge up the load
capacitance unless there is a short. If the voltage
across the load exceeds 200mV, the test is truncated
and normal power-up is allowed to proceed. If the volt-
age across the load does not reach 200mV in the
220ms period that the current is on, the load is
assumed to be shorted and the current to the load from
LP is shut off. The MAX5938A will timeout for 16 x t
then retry the load-probe test. The MAX5938L will latch
the fault condition indefinitely until ON and OFF are
cycled low for 1.5ms or the power is recycled.
In the application, the current-limiting resistor should be
selected to minimize the current pulled through the
load while guaranteeing that it will charge the maximum
expected load capacitance to 220mV in 90ms. These
parameters are the maximum load-probe test voltage
and the minimum load-probe current pulse period,
respectively. The maximum current possible is 1A,
which is adequate to test a load capacitance as large
as 190,000µF over the typical telecom operating
voltage range.
LOAD
OK
TIMING
V
LOGIC
OUT
I
TEST
LP
(A) = C
IN
R
LP
I
TEST
LOAD,MAX
LP
Step Immunity,
. During the test, this switch is
I
C
LOAD
LOAD
(F) x 220mV / 90ms
LOAD
LP