Texas Instruments TPS7B4255EVM-062 User manual

User’s Guide
TPS7B4255EVM-062 Evaluation Module
ABSTRACT
Figure 1-1. TPS7B4255EVM-062 Evaluation Module
This user's guide describes the operational use of the TPS7B4255EVM-062 evaluation module (EVM) as
a reference design for engineering demonstration and evaluation of the TPS7B4255-Q1 low-dropout linear
regulator (LDO). Included in this user's guide are setup and operating instructions, thermal and layout guidelines,
a printed-circuit board (PCB) layout, a schematic diagram, and a bill of materials (BOM).
Throughout this document, the terms evaluation board, evaluation module, and EVM are synonymous with the
TPS7B4255EVM-062.
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Table of Contents
1 Introduction.............................................................................................................................................................................3
1.1 Before You Begin............................................................................................................................................................... 3
2 TPS7B4255EVM-062 Schematic............................................................................................................................................ 4
3 Setup........................................................................................................................................................................................5
3.1 LDO Input/Output Connector Descriptions.........................................................................................................................5
3.2 Optional Load Transient Input/Output Connector Descriptions..........................................................................................6
3.3 TPS7B4255-Q1 LDO Operation and Component Selection.............................................................................................. 6
3.4 Optional Load Transient Circuit Operation......................................................................................................................... 9
4 Board Layout.........................................................................................................................................................................10
5 Bill of Materials..................................................................................................................................................................... 12
List of Figures
Figure 1-1. TPS7B4255EVM-062 Evaluation Module................................................................................................................. 1
Figure 2-1. Schematic..................................................................................................................................................................4
Figure 3-1. TPS7B4255EVM-062 Turn-On..................................................................................................................................7
Figure 3-2. TPS7B4255EVM-062 With Current Probes Attached............................................................................................... 8
Figure 3-3. TPS7B4255EVM-062 Load Transient Results: 50-μA to 70-mA Load Step..............................................................9
Figure 3-4. TPS7B4255EVM-062 Load Transient Results: 70-mA to 50-μA Load Step..............................................................9
Figure 4-1. Top Assembly Layer and Silkscreen....................................................................................................................... 10
Figure 4-2. Top Layer Routing................................................................................................................................................... 10
Figure 4-3. Internal Layer 1....................................................................................................................................................... 10
Figure 4-4. Internal Layer 2....................................................................................................................................................... 10
Figure 4-5. Internal Layer 3........................................................................................................................................................11
Figure 4-6. Internal Layer 4........................................................................................................................................................11
Figure 4-7. Bottom Layer Routing..............................................................................................................................................11
Figure 4-8. Bottom Assembly Layer and Silkscreen.................................................................................................................. 11
Trademarks
LeCroy™ is a trademark of Teledyne LeCroy.
Kapton® is a registered trademark of DuPont.
All trademarks are the property of their respective owners.
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1 Introduction
The Texas Instruments' TPS7B4255EVM-062 evaluation module (EVM) helps designers evaluate the operation
and performance of the TPS7B4255-Q1 LDO voltage regulator. As shown in Table 1-1, the TPS7B4255EVM-062
contains one TPS7B4255-Q1 LDO voltage regulator in the SCT-595 package. An optional load transient circuit
is also included to assist the user with high-speed load transient testing. To simplify current measurements, an
input current loop is included.
Table 1-1. Device Information
EVM ORDERABLE NUMBER VOUT PART NAME PACKAGE
TPS7B4255EVM-062 Adjustable - tracking TPS7B4255QDYBRQ1 5-pin SCT-595
1.1 Before You Begin
This evaluation module is not encapsulated and has exposed terminals with voltages that are connected to the
main power supply. The following warnings are noted for the safety of anyone using or working close to the
TPS7B4255EVM-062. Observe all safety precautions.
WARNING
Failure to adhere to these steps or to not heed the safety requirements at each step may lead to
shock, injury, and damage to the hardware. Texas Instruments is not responsible or liable in any way
for shock, injury, or damage caused by negligence or failure to heed advice. If you are not trained
in the proper safety of handling and testing power electronics please do not test this evaluation
module.
CAUTION:
!
Caution! Do not leave EVM powered when unattended.
HOT SURFACE:
Caution Hot Surface! Contact may cause burns. Do not touch. Please take the proper
precautions when operating.
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2 TPS7B4255EVM-062 Schematic
Figure 2-1 shows a schematic for the TPS7B4255EVM-062.
GND
1.00k
R17
DNP
TP1
GND
J3 J4
J10J9
1
2
J6
Vin Max = 45V Vout Max = 45V
Iout Max = 70mA
1nF
100V
C20
DNP
VDD
A1 OUTH A2
OUTL B2
IN-
C2 GND B1
IN+
C1
LMG1020YFFR
U3
1
2 3 4 5
J21
J20
VDD
J25
GND
50V
10uF
C19
50V
10uF
C18
1.00k
R5
DNP
1
2
J15
DNP
50V
0.1uF
C17
154
R12
DNP 154
R13
DNP
154
R11
DNP
154
R10
DNP
1 2
3 4
J17
DNP
GND
ADJ/EN
VIN
ADJ/EN
VOUT
154
R9
DNP
100V
1pF
C14
DNP
0
R18
DNP
0
R14
DNP
1
2
3
4
5
J26
DNP
1nF
100V
C21
DNP
0
R19
DNP
J18 J19
1
2
3
4
5
J22
DNP
50V
0.015uF
C16
DNP
49.9
R21
GND
GND
J23
TP3
1
2
J7
IN
3OUT 4
ADJ/EN
1GND 2
GND 5
TPS7B4255QDYBRQ1
U1
100V
1uF
C2
DNP
100V
1µF
C5
DNP
50V
1uF
C9
DNP
VO 1
FB/NC
2GND 4
GND 5
GND 6
GND 3
VI
8
EN
7PAD 9
TPS7B8401QWDRBRQ1
U2
VIN
TP2
GND
12
34 56
J14
8V
17.8k
R6
30.0k
R7
48.7k
R8
5V
3.3V
GND
100nF
100V
C10
DNP
10k
R3
DNP
10k
R1
DNP
1
2
J11
1
2
J5
1
2
3
J12
GND
10µF
25V
C11
GNDGND
D1
Iin Max = 70mA
4.7µF
50V
C1
DNP
1.00
R2
DNP
4.7µF
50V
C15
DNP
1.00
R20
DNP
1
32
4
Q1
4.75V Min
5.4V Max
5V Nom
1
2
3
4
5
J2
1
2
3
4
5
J1
GND
1
2
J16
DNP
VIN
GND
J8
J24
100V
1uF
C3
DNP
100V
1uF
C6
DNP
1µF
50V
C7
DNP
VDD
1
2
J13
DNP
VIN
GND
VOUTVIN
487
R15
442
R16
1µF
50V
C4
1µF
50V
C8
100nF
100V
C12
10nF
50V
C13 200k
R4
GND
Optional Load
Transient Circuit
Figure 2-1. Schematic
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3 Setup
This section describes the jumpers and connectors on the EVM, and how to properly connect, set up, and use
the TPS7B4255EVM-062. Section 3.1 and Section 3.3 describe the test setup and operation for the TPS7B4255-
Q1 LDO. Section 3.2 and Section 3.4 describe the test setup and operation of the optional load transient circuit.
3.1 LDO Input/Output Connector Descriptions
3.1.1 VIN and GND
VIN and GND are the connection terminals for the input supply. The VIN terminal is the positive connection, and
the GND terminal is the negative (that is, ground) connection.
3.1.2 VOUT and GND
VOUT and GND are the connection terminals for the output load. The VOUT terminal is the positive connection,
and the GND terminal is the negative (that is, ground) connection.
3.1.3 EN
EN is a 3-pin header used to enable or disable the TPS7B84-Q1, which in turn enables the TPS7B4255-Q1.
The center pin of the 3-pin header is tied to the TPS7B84-Q1 EN input. When the 2-pin shunt is placed across
the right two pins of the header, VIN is shorted to EN and the TPS7B84-Q1 is enabled. When the 2-pin shunt is
placed across the left two pins of the header, GND is shorted to EN and the TPS7B84-Q1 is disabled.
If the TPS7B84-Q1 is not to be used to supply the ADJ/EN signal for the TPS7B4255-Q1, remove jumper J11
and use TP1 to drive ADJ/EN directly, or a combination of J5, R1, R3, C10 to configure ADJ/EN to be a function
of the input voltage.
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3.2 Optional Load Transient Input/Output Connector Descriptions
3.2.1 VDD and GND
VDD and GND are the connection terminals for the input supply of the load transient circuit. The VDD terminal is
the positive connection, and the GND terminal is the negative (that is, ground) connection.
3.2.2 J15
J15 is an optional connection for the user to make measurements or apply loads to the output of the LDO.
3.2.3 J18
J18 is an optional connection to insert a damping circuit across the load transient MOSFET drain to source
voltage.
3.2.4 J19
J19 is an optional connection to insert capacitance or additional load across the drain to source of the load
transient MOSFET.
3.2.5 J21
J21 is the connection for the function generator to drive the gate driver device. J21 is terminated by the 50-Ω
resistor, R21.
3.2.6 J22
J22 is a high-frequency kelvin connection that allows accurate measurements of the load transient MOSFET
drain to source voltage.
3.2.7 J23
Short J23 to enable the gate driver.
3.2.8 J26
J26 is a high-frequency kelvin connection that allows accurate measurements of the load transient MOSFET
gate to source voltage.
3.2.9 TP3
TP3 is the test point used to enable the gate driver device. Tie this pin to GND to enable the gate driver.
3.3 TPS7B4255-Q1 LDO Operation and Component Selection
The TPS7B4255EVM-062 evaluation module contains the TPS7B4255-Q1 LDO with input and output capacitors
installed. These three components provide an implementation example, as illustrated by the white boxes
in Figure 3-2. The prepopulated capacitors are sized to ensure the minimum capacitance requirements are
maintained under all normal operating conditions. Optional pads are available to test the LDO with additional
setpoint options, as well as input and output capacitors beyond what is already installed on the EVM.
Setpoint resistors are prepopulated on the TPS7B4255EVM-062 to configure the TPS7B84-Q1 LDO with an
output voltage of 3.3 V, 5 V, or 8 V. With a shunt placed across the pins of jumper J11, the output of the
TPS7B84-Q1 supplies the ADJ/EN pin of the TPS7B4255-Q1. If a different voltage than the TPS7B84-Q1 output
is desired to drive the ADJ/EN pin, remove the shunt from jumper J11 and use a combination of J5, R1, R3, and
C10 to configure the ADJ/EN pin to be a function of the input voltage. Alternatively, TP1 can be used to directly
drive ADJ/EN with an external voltage source.
The TPS7B84-Q1 LDO can be enabled or disabled by using the J14 3-pin header:
• Place a 2-pin shunt across the header to tie VIN to EN to enable the device
• Place a 2-pin shunt across the header to tie GND to EN to disable the device
Alternatively, by connecting an external function generator to TP2 (EN) and a nearby GND post (J9), the
user can enable or disable the TPS7B84-Q1 LDO after VIN is applied. Figure 3-1 illustrates the result of the
TPS7B4255EVM-062 during turn-on. Jumper J14 has a shunt to connect EN of the TPS7B84-Q1 to VIN to
enable the device for this turn-on plot.
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Figure 3-1. TPS7B4255EVM-062 Turn-On
If desired, a current probe can be inserted in the EVM as illustrated in Figure 3-2 to measure the input and
output current. The slots were sized to fit most current probes, such as the LeCroy™ AP015 or CP031 current
probes.
The board layout is designed such that the Iin current probe slot does not detect any current that goes to the
TPS7B84-Q1 circuit or its peripherals during start up or during any other operational mode. Thus, the Iin current
probe slot can be used to isolate and accurately measure current into the TPS7B4255-Q1 solution.
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Figure 3-2. TPS7B4255EVM-062 With Current Probes Attached
The user has two options for providing a DC load on the output of the TPS7B4255-Q1. J7 can be used to place
a DC load that flows through the current sense path on the output of the LDO. Alternatively, the J4 (VOUT) and
J10 (GND) banana connectors can be used for external measurements and loading; however, the IOUT loop
does not sense current flowing through these connectors. In cases where very fast transient tests are performed,
ringing may occur on VIN or VOUT as a result of the PCB parasitic inductance. Placing a strip of wire on the
exposed copper in the current path can reduce this ringing. 10 AWG wire can be used as needed. If ringing
persists, install damping networks by adding a series resistor and capacitor in parallel with VIN. Locations where
damping can be installed include C1 and R2, and C15 and R20.
WARNING
Current probe sensors can be tied to GND and must not come into contact with energized
conductors. See the user manual of your current probe for details. If your current probe has this
limitation, use a thin strip of electrical or Kapton® tape to isolate the current sense path from the
current probe.
Optional kelvin sense points are provided using the SMA connectors J1 (VIN) and J2 (VOUT).
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3.4 Optional Load Transient Circuit Operation
The TPS7B4255EVM-062 evaluation module contains an optional high-performance load transient circuit
to allow efficient testing of the TPS7B4255-Q1 LDO load transient performance. To use the optional load
transient circuit, install the correct components in accordance with the application. Modify the input and output
capacitance connected to the TPS7B4255-Q1 LDO to match the expected operating conditions. Determine the
desired peak current to test and modify the parallel resistor combination of R9, R10, R11, R12, and R13 as
shown:
IPeak =VOUT
R9R10 R11 R12 R13
+IDC (1)
The slew rate of the load step can be adjusted by C14, R14, R15, and R16. In this section, only R15 and R16
are adjusted to set the slew rate. For a 0-mA to 70-mA to 0-mA load step, use Table 3-1 to select a value of R15
and R16 that results in the desired rise or fall time.
Table 3-1. Suggested Ramp Rate Resistor Values
R15 R16 Rise, Fall Time
3.4 kΩ 2.1 kΩ 700 ns
1.69 kΩ 1.1 kΩ 350 ns
604 Ω 383 Ω 140 ns
332 Ω 169 Ω 70 ns
121 Ω 69.8 Ω 35 ns
37.4 Ω 0 Ω 14 ns
After the EVM is modified (if needed), connect a power supply to banana connectors J20 (VDD) and J25 (GND)
with a 5-V DC supply and a 1-A DC current limit. As illustrated in Figure 3-3 and Figure 3-4, the TPS7B4255-Q1
transient response is very fast and the output voltage recovers in well under 1 ms after the initial load transient.
Use a pulse-duration limit of 1 ms to prevent excessive heating of the pulsed resistors (R9, R10, R11, R12, and
R13). Configure a function generator for the 50-Ω output, in a 0-V DC to 5-V DC square pulse. If necessary,
burst mode can be configured in the function generator for repetitive, low duty cycle, load transient testing.
Use J14 to short R7 to GND and configure VOUT to be 5-V DC. A 487-Ω resistor is installed on the EVM at R15,
and a 442-Ω resistor is installed on the EVM at R16. These resistors provide approximately 0.5-A/μs slew rate
from both 0 mA to 70 mA and 70 mA to 0 mA. Figure 3-3 and Figure 3-4 provide example test data with R15 =
487 Ω and R16 = 442 Ω. The yellow trace is the input voltage, the red trace is the output voltage, and the blue
trace is the output current. R9, R10, R11, R12, and R13 provide 70 mA of pulsed load. The resulting test data
shows a 50-μA to 70-mA load step on VOUT of the LDO, with only a 1-μF capacitor on the output of the LDO.
Figure 3-3. TPS7B4255EVM-062 Load Transient
Results: 50-μA to 70-mA Load Step
Figure 3-4. TPS7B4255EVM-062 Load Transient
Results: 70-mA to 50-μA Load Step
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4 Board Layout
Figure 4-1 through Figure 4-8 illustrate the board layout for the TPS7B4255EVM-062 PCB.
The TPS7B4255EVM-062 dissipates power, which may cause some components to experience an increase in
temperature. The TPS7B4255-Q1 LDO and pulsed resistors R9, R10, R11, R12, and R13 are most at risk of
raising the junction temperature during normal operation. The LDO may become hot to the touch during normal
operation; see the thermal impedance discussion in the TPS7B4255-Q1 data sheet.
Figure 4-1. Top Assembly Layer and Silkscreen Figure 4-2. Top Layer Routing
Figure 4-3. Internal Layer 1 Figure 4-4. Internal Layer 2
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