MAX5043ETN Maxim Integrated Products, MAX5043ETN Datasheet - Page 18

• Manufacturer Part Number: MAX5043ETN
• Description: Switching Converters, Regulators & Controllers Two-Switch Power IC w/Power MOSFET
• Manufacturer: Maxim Integrated Products

where I
t
events from the current-limit comparator are ignored.
Some testing may be required to fine tune the actual
value of the capacitor.
Calculate the approximate bleed resistance (R
needed for the desired recovery time using the follow-
ing formula:
where t
Choose at least t
range from a few hundred microseconds to a few mil-
liseconds.
The MAX5042/MAX5043 feature a latched shutdown that
terminates switching in the event of a serious fault.
External faults in synchronously rectified power supplies
cause a loss of control for the rectifiers. Either the body or
the external Schottky diodes conduct, resulting in a very
high power dissipation and a quick rise of the power-sup-
ply temperature. A thermal sensor placed on the same
ground plane as the secondary-side rectifiers can sense
this catastrophic increase in temperature and issue a
shutdown signal to PWMSD. Asserting PWMSD stops
switching and latches the fault until the power is cycled.
Connect PWMSD to REG5 to disable latched shutdown.
Shut down the MAX5042/MAX5043 by pulling UVLO to
PWMNEG using an open-collector or open-drain transis-
tor connected to PWMNEG. Pulling HSEN to NEGIN also
shuts down the MAX5042 after a 10ms turn-off delay.
Pulling DEN low also shuts down the MAX5043 with a
1ms turn-off delay. When HSEN is used, the MAX5042
goes through a full hot-swap startup sequence with a
165ms startup delay. The MAX5043 also has a 10ms
delay from when DEN asserts.
Two-Switch Power ICs with Integrated
Power MOSFETs and Hot-Swap Controller
18
sh
is the desired ignore time during which current-limit
______________________________________________________________________________________
FLTINT
RT
is the desired recovery time.
R
= 80µA,
FLTINT
C
FLTINT
RT
= 10 x t
≅
≅
C
FLTINT
I
FLTINT
SH
. Typical values for t
t
1 4
RT
Functional Shutdown
Shutdown Modes
ln
.
×
Latched Shutdown



t
2 3
1 6
SH
.
.



FLTINT
SH
)
The MAX5042/MAX5043 feature internal thermal shut-
down. Internal sensors monitor the high-power areas.
Thermal faults arise from excessive dissipation in the
power FETs or in the regulators. When the temperature
limit is reached, switching is terminated and the regulator
shuts down. The integration of thermal shutdown and the
power MOSFETs result in a very robust power circuit.
The MAX5042 integrates a PWM power IC with a hot-
swap controller. The design allows a power supply built
around the MAX5042 to be safely hot-plugged into a
live backplane without causing a glitch on the power-
supply rail. The hot-swap section operates from
POSINHS to NEGIN. The MAX5042 only requires an
external N-channel MOSFET to provide hot-swap con-
trol. Figures 1 and 3 detail hot-swap functionality.
The MAX5042 controls an external N-channel power
MOSFET placed in the negative power-supply pathway.
When power is applied, the MAX5042 keeps the MOS-
FET off. The MOSFET remains off indefinitely if HSEN is
below 1.26V, POSINHS is below the undervoltage lock-
out level (31V), or the die temperature exceeds
+150°C. If none of these conditions exist for 165ms, the
MAX5042 gradually turns on the MOSFET, allowing the
voltage on HSDRAIN to fall no faster than 10V/ms.
During this period, the PWM block remains in shut-
down. The inrush current through the external MOSFET
(and therefore through the capacitor C
level proportional to its capacitance, and the constant
HSDRAIN slew rate. After the MOSFET completely turns
on, and HSDRAIN falls to its final value, the hot-swap
period is terminated and the PWM section of the IC
powers up.
HSEN offers external control of the MAX5042, facilitat-
ing power-supply sequencing. HSEN can also be used
to change the undervoltage lockout level using an
external divider network, if necessary. Undervoltage
lockout keeps the external hot-swap MOSFET switched
off as long as the magnitude of the input voltage is
below the desired level. There is a 10ms turn-off delay
on the HSEN signal.
A power-good output, HSOK, asserts when the external
MOSFET completely turns on. HSOK is an open-drain
output referenced to NEGIN, and can withstand up to
80V above NEGIN.
MAX5042 Hot-Swap Controller
Thermal Shutdown
IN
) is limited to a