Texas Instruments TPS2398EBM User manual

User’s Guide
1
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User’s Guide

2
EVM IMPORTANT NOTICE
Texas Instruments (TI) provides the enclosed product(s) under the following conditions:
This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION
PURPOSES ONLY and is not considered by TI to be fit for commercial use. As such, the goods being provided
may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective
considerations, including product safety measures typically found in the end product incorporating the goods.
As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic
compatibility and therefore may not meet the technical requirements of the directive.
Should this evaluation kit not meet the specifications indicated in the EVM User’s Guide, the kit may be returned
within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE
WARRANTY MADE BY SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED,
IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY
PARTICULAR PURPOSE.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user
indemnifies TI from all claims arising from the handling or use of the goods. Please be aware that the products
received may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). Due to the open construction
of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic
discharge.
EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE, NEITHER PARTY SHALL BE LIABLE
TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
TI currently deals with a variety of customers for products, and therefore our arrangement with the user is not
exclusive.
TI assumes no liability for applications assistance, customer product design, software performance, or
infringement of patents or services described herein.
Please read the EVM User’s Guide and, specifically, the EVM Warnings and Restrictions notice in the EVM
User’s Guide prior to handling the product. This notice contains important safety information about temperatures
and voltages. For further safety concerns, please contact the TI application engineer.
Persons handling the product must have electronics training and observe good laboratory practice standards.
No license is granted under any patent right or other intellectual property right of TI covering or relating to any
machine, process, or combination in which such TI products or services might be or are used.
Mailing Address:
Texas Instruments
Post Office Box 655303
Dallas, Texas 75265
Copyright 2002, Texas Instruments Incorporated

3
DYNAMIC WARNINGS AND RESTRICTIONS
It is important to operate this EVM within the input voltage range of 0 Vdc to100 Vdc.
Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM.
If there are questions concerning the input range, please contact a TI field representative prior to connecting
the input power.
Applying loads outside of the specified output range may result in unintended operation and/or possible
permanent damage to the EVM. Please consult the EVM User’s Guide prior to connecting any load to the EVM
output. If there is uncertainty as to the load specification, please contact a TI field representative.
During normal operation, some circuit components may have case temperatures greater than 50°C. The EVM
is designed to operate properly with certain components above 50°C as long as the input and output ranges are
maintained. These components include but are not limited to linear regulators, switching transistors, pass
transistors, and current sense resistors. These types of devices can be identified using the EVM schematic
located in the EVM User’s Guide. When placing measurement probes near these devices during operation,
please be aware that these devices may be very warm to the touch.
Mailing Address:
Texas Instruments
Post Office Box 655303
Dallas, Texas 75265
Copyright 2002, Texas Instruments Incorporated

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4Evaluation Modules for −48-V Hot Swap Controllers
Evaluation Modules for −48-V Hot Swap Controllers
Systems Pow
er
Contents
1 Introduction 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 The −48-V Hot Swap Controller EVM 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Getting Started 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Using the Evaluation Modules to Evaluate the TPS2398 and TPS2399 12. . . . . . . . . . . . . . . . . .
1 Introduction
This User’s Guide describes the use and features of the simple −48-V hot swap evaluation
module (EVM). This EVM can be used to learn about the TPS2398 and TPS2399 hot swap
controller integrated circuits (ICs) from Texas Instruments (TI). The TPS2398 and TPS2399 are
negative voltage hot swap controllers intended for use in systems needing to hot swap telecom
distribution-level voltages. They integrate inrush current control, peak current limiting, electronic
circuit breaker, enable input, and current fault indication. The EVM is a PCB-based tool featuring
either device, and can be used to evaluate device operation in simulated live insertion events.
1.1 Features
The following list highlights some of the features of the TPS2398 and TPS2399.
•Wide input supply range of −36 V to −80 V
•Transient rating to −100 V
•Programmable current limit
•Programmable current slew rate
•Enable input (EN)
•Fault timer to eliminate nuisance trips
•Open-drain power good output (PG)
•8-pin MSOP package

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1.2 Description
The TPS2398 and TPS2399 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 TPS2398 latches off in response to current faults. The TPS2399 periodically retries the
load, to test for the continued existence of a fault.
2 The −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-µF 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 TPS2398 and TPS2399, 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 −48−V hot swap EVM is shown in Figure 1.

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6Evaluation Modules for −48-V Hot Swap Controllers
Figure 1. Evaluation Module Top Assembly
2.2 EVM Schematic Diagram and List of Materials
The EVM schematic diagram is shown in Figure 2.

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Evaluation Modules for −48-V Hot Swap Controllers
1 2 3 4
8 7 6 5
RTN
GATE
ISNS
−VIN
EN FLTTME IRAMP
TP7
TP6
Q1
+ +
TP13
TP14
TP15
TP16
J3 J4
VOUT
+
VOUT
−
TP4
TP3
1
C5 USER C1
1000 pF
12345
SW1
TP1
D1
C8 USER
1
TP2
OFF
ON
ENABLE
TP12TP10
J2
−48 V_IN
TP8
S2
TP11TP9
S1 OFF
ON
J1
−48 V_RTN
TP5
POWER
1
C6 100 µF 100 V
C7 100 µF 100 V
R5 20 kΩ 1 W
R4 20 mΩ 0.5 W
C2 0.01 µF
C3 0.047 µF
C4 0.1 µF
C9 0.082 µF
R2 7.32 kΩ 1/8 W, 1%
R1 200 kΩ 1/8 W, 1%
R3 12 kΩ 1 W
R6 20 kΩ 1 W
UDG−03018
1
U1
TPS2398DGK TPS2399DGK
PG
Power Good
IRF530S
1Not installed on −001 or −002 assemblies.
Figure 2. −48-V Hot Swap Evaluation Module Schematic

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8Evaluation Modules for −48-V Hot Swap Controllers
Table 1. List of Materials
REFERENCE
QUANTITY
DESCRIPTION
MANUF
PART NUMBER
REFERENCE
DESIGNATOR −002 −001
DESCRIPTION
MANUF
PART NUMBER
U1 1 − IC, −48-V Hot Swap Controller, w/Retry Texas
Instruments TPS2399DGK
U1 − 1 IC, −48-V Hot Swap Controller, Latching Texas
Instruments TPS2398DGK
TP1−TP4, TP6,
TP7, TP9, TP11,
TP13, TP15 10 10 Jack Test Point, red Farnell 240−345
TP5, TP8, TP10,
TP12, TP14,
TP16 6 6 Jack, test point, black Farnell 240−333
S1 1 1 Switch, toggle, SPDT, PC Mnt. E−Switch 100SP1T1B1M2QE
S2 1 1 Switch, slide, SPDT, right angle, 200 mA E−Switch EG1213
SW1 1 1 Switch, dip, 5-position, SPST CTS 219−05MS
R1 1 1 Resistor, 200 kΩ, 0.125W, 1% Panasonic ERJ−8ENF2003
R2 − − Resistor, 0.125W, 1% Standard Standard
R3 1 1 Resistor, 12 kΩ, 1W, 5% Venkel CR2512−1W123J
R4 1 1 Resistor, 0.02 Ω, 0.5W, 1% Vishay−Dale WSL−2010 .020<1%
R5, R6 2 2 Resistor, 20 kΩ, 1W, 5% Venkel CR2512−1W203J
Q1 1 1 XSTR, MOSFET, N−channel, V(BR) > 100V Int’l Rectifier IRF530S
J1, J2, J3, J4 4 4 Jack, banana, non-insulated, PC mount Pomona 3267
D1 1 1 Diode, LED, green Panasonic LN1361C
C1 1 1 Capacitor, ceramic, 1000 pF, 25 V, 10%, X7R Vitramon VJ0805Y102KXXA
C2 1 1 Capacitor, ceramic, 0.01 µF, 16 V, 10%, X7R Vitramon VJ0805Y103KXJA
C3 1 1 Capacitor, ceramic, 0.047 µF, 16 V, 10%, X7R Vitramon VJ0805Y473KXJA
C4 1 1 Capacitor, ceramic, 0.1 µF, 16 V, 10%, X7R Vitramon VJ0805Y104KXJA
C5 − − Capacitor, ceramic, 0805 Standard Standard
C6 1 1 Capacitor, aluminum. electrolytic, 100 µF, 100 V, 20% Vishay EKA00DE310L00
C7 − − Capacitor, aluminum. electrolytic, 100 µF, 100 V, 20% Vishay EKA00DE310L00
C8 − − Capacitor, ceramic, 1206 Standard Standard
C9 1 1 Capacitor, ceramic, 0.082 µF, 16 V, 10%, X7R Vitramon VJ0805Y823KXJA
N/A 4 4 Spacer, nylon, hex, #6−32, 0.625” Eagle 14HTSP020
N/A 4 4 Screw, nylon, round head, #6−32, 0.25” Eagle 010632R025
N/A 1 1 PCB, FR−4, 2−layer, SMOBC, 3.225” x 2.237”, 0.062”
thk. Texas Instruments HPA024

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Evaluation Modules for −48-V Hot Swap Controllers
2.3 −48-V Hot Swap EVM Operating Specifications
The −48−V hot swap EVM is intended to allow some degree of user reconfiguration. This allows
designers to set up the circuit to better represent the characteristics of their target application.
Potential modifications include changing the current limit threshold, the inrush limiting, the fault
timing, and load characteristics. However, under no circumstances should the EVM kit be
operated beyond the absolute maximum conditions specified in Table 2.
Table 2. Absolute Maximum Ratings (1)(2)
PARAMETER MIN MAX UNITS
Input voltage range, J1 −0.3 100 V
Load current, J3 −2.25
A
Load return current, J4 2.25 A
Ambient operating temperature range −40 85 °C
(1) All voltages are with respect to the PCB −48-V_IN node at J2.
(2) Currents are positive into and negative out of the specified terminal.
As supplied from the factory, the −48-V hot swap EVM is configured for operation under the
following target conditions, shown in Table 3.
Table 3. Recommended Operating Conditions (1)(2)
PARAMETER MIN TYP MAX UNITS
Input supply voltage, J1 36 48 80 V
Nominal load current, J3 −1
A
Nominal load return current, J4 1A
Operating temperature range −40 85 °C
(1) All voltages are with respect to the PCB −48-V_IN node at J2.
(2) Currents are positive into and negative out of the specified terminal.
3 Getting Started
3.1 Equipment Requirements
The following test equipment is required to use the −48-V hot swap EVM (TPS2398EVM or
TPS2399EVM).
•Power supply, 80 Vdc at 3-A minimum
•Oscilloscope
•Digital voltmeter (DVM)
The individual DIP switches of SW1 are labeled numerically on the PCB silkscreen. Throughout
this document, references to the DIP switches (e.g., SW1−1) apply to these screened labels, not
to any marking on the switch. However, to determine the ON and OFF positions of the switches,
use the labeling on the switch body itself.

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10 Evaluation Modules for −48-V Hot Swap Controllers
3.2 Verifying the EVM Operation
The following procedure steps may be used to verify functional operation of the EVM after
receipt.
3.2.1 Equipment Setup
1. On the EVM board, place the POWER switch in the OFF position, and verify that the
ENABLE switch is in the OFF position.
2. Set the DIP switches 1 through 4 of switch SW1 to the ON position.
3. Turn on the power supply and adjust the output for about 48 V. Verify the supply current
limit is set to allow at least 3 A. Turn off the power supply.
4. Connect the EVM and test equipment as shown in Figure 3.
5. On the oscilloscope, set the channel amplifiers to the following scales:
•CH1: 20 V/div
•CH2: 2 V/div
•CH3: 5 V/div
•CH4: 20 V/div
For easier correlation to the information in this document, the scope trace baselines can be
positioned as shown in Figure 4.
6. Set the scope to trigger on the rising edge of Channel 1, at approximately a 10-V level.
Set the scope timebase to 10 ms, and the trigger mode to NORMAL.
UDG−03019
OSCILLOSCOPE
CH 1
CH 2
CH 3
CH 4
POWER
SUPPLY
−+
J2 (−48V_IN)
J1 (−48V_RTN)
TP2
TP4
TP3
TP16
TP15
TP14
TP8/TP12 (GND)
VOLTS COM
DIGITAL
VOLTMETER
−48-V Hot Swap Controller
Evaluation Module
(TPS2398EVM/TPS2399EVM)
Figure 3. Evaluation Module Setup

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Evaluation Modules for −48-V Hot Swap Controllers
3.2.2 Functional Test
1. Turn on the power supply. On the EVM, place the POWER switch in the ON position.
Verify the power good LED (D1) is OFF. Verify the DVM reading is 0 ±100 mV.
2. Place the ENABLE switch in the ON position. Verify the green power good LED turns on,
and the DVM now displays approximately the input supply voltage level. The scope should
have acquired a sweep similar to that shown in Figure 4.
The brief fault timing ramp which is shown in Figure 4 FLTTIME trace may or may not be
present, depending on the actual values of the timing parameters for the particular board
being used. If the load voltage ramps to full input potential during the initial reduced rate
ramp period, then fault timing does not initiate.
3. Place either the POWER or ENABLE switch (or both) in the OFF position to remove power
from the VOUT terminals.
EN
IRAMP
FLTTIME
VOUT−
Figure 4. Load Ramp-Up Waveforms

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12 Evaluation Modules for −48-V Hot Swap Controllers
4 Using the Evaluation Module to Evaluate the TPS2398/99
Procedures similar to the steps of Section 3.2.2 for functional test of the EVM can also be used
to continue evaluation of the TPS2398 and TPS2399 hot swap controllers. Additional details
about the EVM features are provided in this section.
The ENABLE switch can be used to enable and disable power to the load (i.e., the VOUT+ and
VOUT− terminals), when the POWER switch is in the ON position.
Also, with the ENABLE switch in the ON position, the POWER switch can be toggled ON and
OFF to simulate hot swap events with the device set up to automatically power up the load.
4.1 Test Points
The −48-V hot swap EVM contains the test points listed in Table 4, for waveform and voltage
monitoring.
Table 4. Test Points
TEST
POINT SIGNAL NAME DESCRIPTION
TP1 PG Open-drain, active-low indication of a load power good condition. On the EVM, this signal drives the green
LED.
TP2 EN Device enable input to turn on/off power to the load.
TP3 FLTTIME Fault timing waveform of the TPS2398/99.
TP4 IRAMP Current ramp control output waveform.
TP5 −VIN Negative supply input and reference pin for the TPS2398/99. On the EVM, this is connected to −48V_IN.
TP6 ISENS Current sense input of the controller.
TP7 GATE Gate drive for external FET Q1.
TP8 −VIN Secondary test point on device reference node.
TP9
−48V_RTN
The high side of input power to the EVM. When used in conjunction with a lab supply, this connects to the
TP11 −48V_RTN
The high side of input power to the EVM. When used in conjunction with a lab supply, this connects to the
(+) jack. (Test points are on plug-in side of the POWER switch.)
TP10
−48V_IN
The low side of input power to the EVM. When used in conjunction with a lab supply, this connects to the
TP12 −48V_IN
The low side of input power to the EVM. When used in conjunction with a lab supply, this connects to the
(−) jack.
TP13
VOUT+
High side of switched (load) output power.
TP15 VOUT+ High side of switched (load) output power.
TP14
VOUT−
Low side of switched (load) output power.
TP16 VOUT− Low side of switched (load) output power.
4.2 Load Capacitors
Capacitor patterns C6 and C7 are available on the EVM for installation of components to
represent the module input bulk capacitance; i.e., the load capacitance seen by the hot swap
interface circuit. As supplied from the factory, the EVM contains a 100-µF aluminum electrolytic
installed at C6. Further customization to approximate the user’s application can be done using
either C6 or C7. When installing capacitors in these mounting locations, care should be taken to
observe the polarity marking on the PCB silkscreen, and to use appropriately rated capacitors
for voltage withstanding. Generally, telecom applications should use 100-V minimum rated
capacitors.
Banana jacks J3 and J4 are also connected across the output terminals, in parallel with C6 and
C7. These jacks can be used to connect additional loads to the EVM board.

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Evaluation Modules for −48-V Hot Swap Controllers
4.3 Changing the Current Limit Threshold
During power-up of a plug-in card, the TPS2398 and TPS2399 limit the peak inrush current
drawn by the discharged bulk capacitance. The LCA senses load current as the drop across an
external sense resistor. Current is regulated by slewing the gate of the pass FET to maintain the
voltage drop at an internally set level, nominally 40 mV. Therefore, the peak current level can be
established by selecting the appropriate sense resistor value. On the −48-V hot swap EVM, this
resistor is R4. The default value of R4 is 20 mΩ. To modify the current limit threshold, a new
sense resistor value can be determined from Equation 1.
R4 vVMAX
IMAX
where
•VMAX is the sense voltage limit
•IMAX is the desired current limit threshold
Using the device minimum value of 33 mV for VMAX along with the required minimum load
current ensures that minimum amount of current can always be supplied to the load. For
example, a particular line card is expected to draw a maximum of 1.2 A, when the power bus is
at its operating minimum level of −36 V, once the card is powered up and operating normally. For
this load characteristic, a sense resistor value less than 33 mV/1.2 A, or 27 mΩ, is selected. A
25-mΩresistor is the closest approximate standard value that is readily available. A
smaller-value resistor is also acceptable, but carries a corresponding increase in the maximum
current limit.
4.4 Changing the Inrush Slew Rate
The TPS2398 and TPS2399 also feature slew rate limiting as current is ramped to charge the
load capacitance. The slew rate is easily programmed, once the sense resistor is determined,
with a small-value capacitor connected between the IRAMP and −VIN pins. The EVM comes
equipped with three preset capacitor values, selectable either individually or in combination by
closing the appropriate DIP switches of SW1. The default values of the capacitors, and the
corresponding nominal slew rates, are given in Table 5.
Table 5. Default Slew Rates
SW1 DIP REFERENCE
DESIGNATOR INSTALLED VALUE SLEW RATE (A/s)
1 C1 1000 pF 5000
2 C2 0.01 µF 500
3 C3 0.047 µF 106
The EVM can be used to illustrate the relationship between current limit, inrush slew rate, load
values, and the circuit’s fault timing requirements. With only DIP switch SW1−1 closed, the
fastest of the preset slew rates is selected, and only the hard-wired timing capacitor C9 is
connected to the TPS2398 or TPS2399 controller. However, this is sufficient to allow the bulk
capacitor C6 to fully charge, from 0 volts, across the full range of input supply voltages, down to
−80 V. This can be observed by connecting input power as shown in Figure 3, displaying the
VOUT− node on an oscilloscope, and enabling the device.
(1)

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14 Evaluation Modules for −48-V Hot Swap Controllers
To observe the controller response to a load that does not charge up as expected (a shorted or
otherwise excessive load), set switches SW1−1, SW1−2, and SW1−3 to the ON position. This
greatly reduces the inrush (load charging) current slew rate at turn-on, with a corresponding
increase in the amount of time needed to successfully charge the intended load. Increase the
supply level to between approximately 60 V and 80 V, and again enable the device. In this case,
the voltage ramp time is excessively long relative to the programmed fault timer; the controller
times out and turns off the load(1). Again, this can be viewed on an oscilloscope and also in the
failure of the green powergood LED to illuminate. When evaluating the TPS2399, the LED may
ultimately illuminate, indicating capacitor charging is eventually completed on a successive
retry.) If this combination represented the parameters of the target plug-in module, then the
timing capacitance of C9 and C4 (SW1−4 closed) would be more appropriate. The intended
load, in this case, the 100-µF capacitor, can again be charged up over the input voltage range.
The inrush slew rate can be changed, to better match the application requirement, by replacing
any capacitor C1, C2 or C3. The PCB patterns are sized for 0805 ceramic chip capacitors. Use
equation 2 to calculate the new ramp capacitor, CRAMP, value in microfarads.
CRAMP +11
100 R4 ǒdi
dtǓMAX
where
•R4 is the selected sense resistor value, in ohms
•(di/dt)MAX is the desired maximum slew rate, in amperes/second.
4.5 Fault Timing with the TPS2398/TPS2399
Whenever the hot swap controller is limiting current to the load, an on-chip timer is monitoring
this operation against an established time limit. The timeout period is generated by the
constant-current charging of a capacitor at the FLTTIME pin. If current regulation ceases prior to
expiration of the timer, the capacitor is discharged, and normal steady-state operation of the load
either starts or resumes. However, if the timer expires, then the pass FET is turned off, disabling
power to the load, and the PG output assertion is either inhibited or cleared.
On the −48-V hot swap EVM, several capacitor patterns are provided for increasing or otherwise
modifying the timeout period. Capacitor C9 is hard-wired to the device FLTTIME pin, and
provides a minimum fault timer for the default load. C4 and C5 can be switched into the circuit
via DIP switches SW1−4 and SW1−5, respectively. The EVM ships from the factory with a
0.1-µF capacitor installed at C4; C5 is not populated for easier subsequent user modification as
required.
(1) Due to tolerances of various EVM parameters, some units may not fault out under these conditions. Generally, this is due to the fact that the
amount of voltage ramping during the reduced-rate turn-on period will vary from device to device. Some units may be able to charge the load
almost completely during this period, when fault timing is inhibited. A more severe load fault is needed to view the fault response. Additional
capacitance, or even a resistor, can be connected across the VOUT terminals, J3(+) and J4(−) or at C7. If the user is confident the module
is operating correctly, the load can also be shorted out to do this demonstration.
(2)

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Evaluation Modules for −48-V Hot Swap Controllers
If the target application requires fault timing other than that provided by the default EVM setup, a
new value of timing capacitor can be calculated from equation (3). When selecting from the
readily available capacitor values for the result of equation (3), default to a slightly larger, rather
than smaller, capacitor.
CFLT +ǒ55 tFLTǓ
3.75
where
•CFLT is the calculated value in microfarads,
•tFLT is the desired timeout period in seconds
4.6 Using the EN Pin to Adjust Undervoltage Lockout (UVLO)
The TPS2398 and TPS2399 devices have an internal UVLO circuit, which keeps the load
disabled when the input supply voltage is low. The internal threshold is set to a nominal 30 V, at
the RTN input with respect to −VIN, with a maximum specification value of 36 V. This setting is
targeted at general telecom applications. However, it is possible to raise the minimum start-up
threshold, and potentially tighten the tolerance window of the UVLO function, by using the
enable input comparator.
Where the desired UVLO voltage is greater (more negative) than the internal threshold, a
resistor divider on the input supply can be used to enable the load at this minimum voltage level.
The divided down input voltage then drives the EN pin. Resistor patterns R1 and R2 are
provided on the EVM to implement this function. The nominal enable comparator threshold is
1.4 V. Assuming the default R1 value of 200 kΩis used, the value of R2 is determined from
Equation 4.
R2 +1.4 V
ǒVUV *1.4VǓ 200 kW
where VUV is the desired UVLO threshold.
For example, to adjust the nominal UVLO to 40 V, the value of R2 required is 7.25 kΩ, per
equation (4). Using the standard value of 7.32 kΩ, the expected threshold is 39.65 V.
(3)
(4)

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