MAX5921AEVKIT Maxim Integrated, MAX5921AEVKIT Datasheet - Page 3

• Manufacturer Part Number: MAX5921AEVKIT
• Description: Hot Swap & Power Distribution Evaluation Kit for the MAX5920 MAX5921 MAX5939
• Manufacturer: Maxim Integrated

Specifications of MAX5921AEVKIT

• Product: Controllers & Switches
• Supply Voltage - Max: 80 V
• Supply Voltage - Min: 20 V
• Operating Temperature Range: - 40 C to + 85 C
• Power Dissipation: 471 mW
• Supply Current: 0.7 mA

The EV kit circuit ensures that the input voltage is stable
and within the undervoltage and overvoltage thresholds,
which are configured to -32V and -80V, respectively. The
circuit continually monitors the load current so that it
does not exceed the current-limiting threshold of 2.5A
across sense resistor R5 for longer than 0.5ms. During
such an event, the hot-swap controller turns off MOSFET
N1 and restarts the power-up sequence. The PWRGD
output signal is pulled to -VIN during normal opera-
tion and to +VIN by R7 during fault conditions.
The EV kit board features a 90V zener diode (D1) and
a resistor-capacitor (R8-C7) network to allow the EV kit
circuit to withstand -100V input transients. A transient
voltage suppressor diode can also be added at the D2
PC board pads to suppress input transients higher
than -100V. Inrush current control to the output can be
reconfigured by replacing components C2 and R3.
Capacitor C1 may be required when evaluating the
LT1640/LT4250. Refer to the Component Selection
Procedure section on the MAX5921/MAX5939 data
sheet for detailed information.
The EV kit can also be used to evaluate other versions
of the MAX5920, MAX5921, or MAX5939 hot-swap con-
trollers after replacing the MAX5921A IC.
The MAX5921A EV kit can operate from an input source
of -20V to -80V connected across -VIN and +VIN.
However, the EV kit is configured for an operating
range of -32V to -80V. The MAX5921A controller begins
to function when the input voltage exceeds the internal
undervoltage lockout (UVLO) voltage threshold of
-15.4V (typ). It continues to hold the GATE pin low, iso-
lating the power supply from the output until the pro-
grammed undervoltage protection (UVP) threshold of
-32V is exceeded. Once the input voltage exceeds the
UVP threshold, the controller slowly turns on MOSFET
N1 to connect power to the load.
The MAX5921A EV kit UVP threshold is programmed to
-32V and the overvoltage protection (OVP) threshold is
programmed to -80V with external resistors R4, R5, and
R6. If the voltage at +VIN drops below the UVP thresh-
old or exceeds the OVP threshold, the MAX5921A con-
troller turns off MOSFET N1 and the controller pulls the
PWRGD output signal to +VIN to signal a fault (in an
overvoltage condition PWRGD output is not pulled to
+VIN). The controller returns to normal operation and
pulls PWRGD to -VIN if the input voltage returns to with-
in the UVP (-32V) and OVP (-80V) thresholds. The UVP
and OVP thresholds can be reconfigured in the range
of -20V and -80V by replacing resistors R4, R5, and R6.
_______________________________________________________________________________________
UVP and OVP
Input Voltage
MAX5921A Evaluation Kit
Use the following formula to select new resistor values:
where UVP is the desired undervoltage threshold, OVP
is the desired overvoltage threshold, and R6 is typically
10kΩ. The undervoltage threshold must be pro-
grammed to be greater than the internal undervoltage
lockout threshold of -15.4V (typ).
The MAX5921A hot-swap controller provides current-
limiting and current regulation capabilities that protect
against excessive load current and short-circuit condi-
tions. The load current is monitored by sensing the volt-
age across current-sense resistor R1. The current-limit
voltage trip point (V
The EV kit circuit current limit is programmed to 2.5A
with the 20mΩ (2.5A x 20mΩ = 50mV) sense resistor
R1. If the voltage across the sense resistor exceeds
V
age to regulate the load current to 2.5A. If the load cur-
rent is at the regulation limit of 2.5A for more than 0.5ms
(t
external MOSFET to turn off. The MAX5921A will auto-
matically retry after detecting a fault condition. Refer to
the MAX5921/MAX5939 data sheet’s Current Limit and
Electronic Circuit Breaker section for more details.
The MAX5921A enters Autoretry mode when it detects
a current-limit fault condition. In this mode, the hot-
swap controller turns off the MOSFET for a period of
64ms (t
up procedure. The controller cycles on and off until the
fault condition is cleared. The off period (t
defined as t
0.5ms and the duty cycle (DC) of 1/128 are inherent to
the MAX5921A hot-swap controller. Other versions of
the MAX5921 hot-swap controllers are programmed
with t
MAX5920/MAX5921/MAX5939 Hot-Swap Controllers
section).
The MAX5920_ and MAX5939_ hot-swap controllers
latch off after a current-limit fault condition.
LIM
LIM
), the electronic circuit breaker trips, causing the
, the hot-swap controller pulls down the GATE volt-
LIM
OFF
UVP
OVP
of 0.5ms, 1ms, or 2ms (see the Evaluating
) before it attempts to execute a new start-
OFF
=
=
= 1/DC x t
1 255
1 255
.
.
LIM
V
V
) of the controller is 50mV (typ).
Current Limit and Regulation






R
R
LIM
4
4
R
+
, where the t
+
5
R
R
R
+
5
6
5
R
+
+
6
R
R
6
6






LIM
Autoretry
period of
OFF
) is
3