SLUU150 – February 2003
5
Evaluation Modules for Simple –48-V Hot Swap Controllers
1.2
Description
The TPS2390 and TPS2391 simple –48-V hot swap controllers are integrated solutions
optimized for use in nominal –48-V systems. They are used in conjunction with an external
N-channel MOSFET and sense resistor to enable hot swap, the insertion and removal of plug-in
cards or modules in powered systems. Both devices feature inrush current slew rate and peak
magnitude limiting, which are easily programmed by the sense resistor value, and a single
external capacitor. They facilitate implementation of platform control of the electrical connection
or isolation of the protected load, and provide single-line load fault reporting. An on-chip timer,
also set by a single capacitor, provides filtering against nuisance breaker trips. These features
are all incorporated into a tiny 8-pin MSOP package.
The TPS2390 latches off in response to current faults. The TPS2391 periodically retries the
load, to test for the continued existence of a fault.
2
The Simple –48-V Hot Swap Controller EVM
2.1
Module Description
The –48-V hot swap EVM contains all the components needed to implement a complete telecom
hot swap interface. In addition, it contains some additional components and PCB patterns to
facilitate evaluation of the device.
Banana jacks are provided for connection of the user’s power supply. On the switched side of
the hot swap circuit, jacks are also provided for connection of the user’s electronic or resistive
load, if desired. The board also contains two through-hole patterns for the installation of
large-value aluminum electrolytic capacitors. This capacitance is used to simulate the input bulk
capacitance present at a plug-in’s power inputs. The EVM is supplied from the factory with a
100-
µ
F capacitor installed in one of the locations. The second pattern, connected in parallel with
the first, can be used to increase or otherwise modify the amount of load capacitance.
From the input power jacks, power is applied to the hot swap circuit via a toggle switch
connected in-line with the high-side of the power bus. Bounce of the switch contacts helps the
user observe the response of the devices under power-up conditions resembling those of an
actual application. An on-board slide switch is also provided to independently toggle the status
of the device enable input (EN pin).
With the TPS2390 and TPS2391, both inrush slew rate limiting and a fault time-out period are
externally programmable using capacitors. On the EVM, several options are provided for slew
rate limiting, for quick comparison of the effect of capacitor value on this function. The capacitors
can be quickly switched in and out of the circuit via the DIP switch. Fault timing programming is
set up in a similar manner; some amount of capacitance is hard-wired into the circuit, with the
option of switching in additional capacitance.
Test points are provided throughout the circuit for easy voltage monitoring via oscilloscope or
voltmeter. The test point connections are listed in Table 4.
A pictorial of the simple –48–V hot swap EVM is shown in Figure 1.
