Texas Instruments LM73605 User manual

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LM73605 / LM73606 EVM User’s Guide
User's Guide
SNVU579–September 2017
LM73605 / LM73606 EVM User’s Guide
The LM73605 / LM73606 evaluation module (EVM) is designed to help customers evaluate the
performance of the LM73605 / LM73606 synchronous step-down voltage converters. The EVM contains
one LM73605 or LM73606 device in the 30-pin wettable flanks QFN (WQFN) package, as shown in
Table 1. It is capable of delivering 5-V output voltage and up to 5-A (LM73605) or 6-A (LM73606) load
current with exceptional efficiency and output accuracy in a very small solution size. The EVM provides
multiple power connectors and test points, as well as mode setting options and enable input options, for
customer convenience. It also provides a good layout example, which is optimized for EMI performance
and thermal performance.
Table 1. Device and Package Configurations
CONVERTER IC PACKAGE
U1 LM73605 30-pin wettable flanks QFN (WQFN)
6 mm × 4 mm × 0.8 mm
LM73606
Contents
1 Introduction ................................................................................................................... 2
2 Quick Start.................................................................................................................... 3
3 Detailed Descriptions........................................................................................................ 4
4 Schematic..................................................................................................................... 6
5 Board Layout ................................................................................................................. 7
6 Bill of Materials ............................................................................................................. 10
7 Performance Curves....................................................................................................... 13
Trademarks
All trademarks are the property of their respective owners.

Copyright © 2017, Texas Instruments Incorporated
CSS
RT
RSYNC
RENT
RENB
SW
PVIN
PGND CBOOT
VCC
BIAS
EN
AGND
FB
VIN
COUT
CBOOT
CIN
CVCC
VOUT
RFBT
RFBB
L
SYNC/
MODE
RT
SS/TRK PGOOD
VCC
RT
BIAS
SS/TRK
2
3
423
25
24
PVIN
SW
SW
DAP PVIN
PGND
SW
22
26
1
5
CBOOT
SW
PGND
21
6
PGND
PGND
20
7
PGOOD
19
8AGND
9
10
18
17
EN
FB
SYNC/
MODE
16
11
29 28 27
30
13 14 15
12
SW PVIN
NC NC NC NC
NC NC NC NC
Introduction www.ti.com
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LM73605 / LM73606 EVM User’s Guide
1 Introduction
1.1 LM73605 / LM73606 Synchronous Step-Down Voltage Converter
The LM73605/LM73606 family of devices are easy-to-use synchronous step-down DC-DC converters
capable of driving up to 5 A (LM73605) or 6 A (LM73606) of load current from a supply voltage ranging
from 3.5 V to 36 V. The LM73605/LM73606 provide exceptional efficiency and output accuracy in a very
small solution size. Peak-current-mode control is employed. Additional features such as adjustable
switching frequency, synchronization to an external clock, FPWM option, power-good flag, precision
enable, adjustable soft start, and tracking provide both flexible and easy-to-use solutions for a wide range
of applications. Automatic frequency foldback at light load and optional external bias improve efficiency
over the entire load range. The family requires few external components and has a pinout designed for
simple PCB layout with optimal EMI and thermal performance. Protection features include thermal
shutdown, input undervoltage lockout, cycle-by-cycle current limiting, and hiccup short-circuit protection.
The LM73605 and LM73606 devices are pin-to-pin compatible for easy current scaling.
The pin configuration of the LM73605/6 is shown in Figure 1 and the schematic is shown in Figure 2 for
your quick reference. See the LM73605/LM73606 data sheet for more detailed feature descriptions and
design guide.
Figure 1. LM73605/6 Pin Configuration (30-Pin WQFN
Package Top View) Figure 2. LM73605/6 Schematic
1.2 LM73605 / LM73606 Evaluation Module
The LM73605 / LM73606 EVM has three variants to cover a wide range of applications. The options
include LM73605 (5-A maximum DC output current) with 400-kHz switching frequency and 2.2-MHz
switching frequency, and LM73606 (6-A maximum DC output current) with 400-kHz switching frequency,
as listed in Table 2. The output voltage is 5 V.
Table 2. EVM Variants
Label U1 IOUT Switching
Frequency VIN Range VOUT
LM73605EVM-5V-2MHz LM73605 5 A 2.2 MHz 6 to 36 V 5 V
LM73605EVM-5V-400K LM73605 5 A 400 kHz 6 to 36 V 5 V
LM73606EVM-5V-400K LM73606 6 A 400 kHz 6 to 36 V 5 V

www.ti.com Quick Start
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2 Quick Start
1. Connect the voltage supply between VIN and PGND connectors, using short and thick wires.
2. Connect the load of the converter between VOUT and PGND connectors, using short and thick wires.
3. Set the supply voltage (VIN) at an appropriate level between 6 V to 36 V. Set the current limit of the
supply to an appropriate level as well.
4. Turn on the power supply. With the default configuration, the EVM should power up and provide VOUT =
5 V.
5. Monitor the output voltage. The maximum load current should be 5 A with LM73605, or 6 A with
LM73606.
See Figure 3 for the location of the connectors.
Figure 3. Top View of LM73605/LM73606 EVM

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3 Detailed Descriptions
This section describes the connectors and the test points on the EVM and how to properly connect, set up
and use the LM73605/LM73606 EVM. See Figure 3 for a top view of the EVM.
VOUT —Output voltage of the converter.
VOUT connector and test point connect to the power inductor and the output capacitors. Connect
the loading device between VOUT and PGND connectors to provide loading to the converter.
Connect the loading device to the board with short and thick wires to handle the large DC output
current.
PGND —Ground of the converter.
It is connected to the PGND and AGND of the device, as well as the input and output capacitors.
PGND is the current return path for both supply voltage and load. Connect to supply and load
grounds with short and thick wires.
VIN —Input voltage to the converter.
VIN connector and test point connect to the input capacitors and the PVIN pins of the
LM73605/LM73606. Connect the supply voltage from a power supply or a battery between VIN and
PGND connectors as power input to the board. The voltage range should be higher than 3.5 V for
the device to be active. VIN higher than 6 V provides regulated 5 V output voltage. VIN should be no
higher than 36 V to avoid damaging the device. The current limit on the supply should be high
enough to provide the needed supply current. Otherwise the supply voltage will not maintain the
desire voltage. The supply voltage should be connected to the board with short and thick wires to
handle the pulsing input current. If long cables are used to power up the board, the damping
capacitor CBULK located on the bottom side of board should be added, to avoid oscillation between
the cable parasitic inductance and the low-ESR ceramic capacitors.
VIN-EMI —Input voltage to input filter of the converter
If the input filter is desired between the supply voltage and the LM73605/6, connect the supply
voltage between VIN-EMI and GND-EMI. The supply voltage should be connected to the board with
short and thick wires to handle pulsing input current.
GND-EMI —Ground connection near the input filter
This is the current return path for the supply connected to VIN-EMI. It provides a direct connection
to the input filter capacitors to best filter the conducted noises generated from the PCB. Use VIN-
EMI and GND-EMI connection if input filter is used and conducted EMI test is desired.
Input Filter—Prevent noise from contaminating supply voltage
The input filter consists of C-FLTs, L-IN and CBULK, located on the bottom side of the PCB. To
include the input filter in the power path, connect the supply voltage between the VIN-EMI and
GND-EMI connectors. The output of the filter is connected to the VIN net, which is connected to the
PVIN pins of the LM73605/LM73606 and the input capacitors. Note that the input filter components
are not mounted on the PCB by default.
Conducted EMI arises from the normal operation of switching circuits. The ON and OFF actions of
the power switches generate large discontinuous currents. The discontinuous currents are present
at the input side of buck converters. Voltage ripple generated by discontinuous currents can be
conducted to the voltage supply of the buck converter via physical contact of the conductors.
Without control, excessive input voltage ripple can compromise operation of the source. The input
filter helps to smooth out the voltage perturbations leading to the source.
Preliminary EMI test results are shown in Section 7.4.
EN — Test point to monitor the EN pin of the device
This test point is to monitor the voltage on the device EN pin.
EN Jumper —Set EN pin options
As noted on the board, this jumper is to select which voltage is used to enable the device.
1. PIN-1 to PIN-2: EN is connected to EN-EXT test point through a resistor divider;
2. PIN-2 to PIN-3 (default): EN is connected to VIN through a resistor divider.

www.ti.com Detailed Descriptions
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The divider, RENT and RENB, locates right above the EN jumper on the PCB.
The default setting is jumper on PIN-2 and PIN-3. The board will start when VIN is about 3.5 V with
this setting. The EN voltage is calculated by Equation 1.
VEN = VIN × RENB / (RENT + RENB) (1)
When PIN-1 and PIN-2 are connected, the EN voltage is calculated by Equation 2.
VEN = VEN-EXT × RENB / (RENT + RENB) (2)
If a resistor divider is not desired, the RENB can be removed from the board and the EN pin voltage
will be equal to either EN-EXT or VIN voltage, depending on the jumper location. It is recommended
to keep RENT as a current limiting and noise filtering resistor at EN pin.
EN-EXT —External voltage input to drive EN
When EN jumper has PIN-1 and PIN-2 connected, the enable threshold is driven by the voltage on
the EN-EXT test point. The EN pin voltage can be found by Equation 2.
Remove RENB from the board if it is desired to have the same voltage on the EN pin as the EN-EXT
voltage.
PGOOD —Test point to monitor the PGOOD pin
PGOOD test point is used to monitor the power-good flag. This flag indicates whether the output
voltage has reached its regulation level. The PGOOD pin of the device is an open-drain output that
is pulled up to VOUT on this board through RPG resistor.
SYNC/MODE Jumper —Operation mode setting and synchronization clock input
As noted on the PCB, the SYNC/MODE jumper is used to select the desired light-load operation
mode.
1. PIN-1 to PIN-2: FPWM mode;
2. PIN-2 to PIN-3 (default): auto mode;
3. Open, connect external clock input to SYNC test point for synchronization and FPWM mode.
The default is PIN-2 and PIN-3 connected together and the device will operate in auto mode at light
loads. With auto mode, discontinuous conduction mode (DCM) and pulse frequency modulation
(PFM) mode are employed at light loads to provide high efficiency. PFM mode also provides very
low quiescent current at no load. At heavier load, when inductor current is in DCM or continuous
conduction mode (CCM) operation, the switching frequency is determined by the RT resistor on the
board, which is either 400 kHz or 2.2 MHz.
When PIN-1 and PIN-2 are connected, the device operates in the force PWM (FPWM) mode. In
FPWM, the inductor current will be in CCM regardless of load. The switching frequency is the same
at light loads as that of heavier loads. The switching frequency will be programmed by RT resistor
on the board, which is either 400 kHz or 2.2 MHz.
If synchronization to an external clock is desired, leave the SYNC/MODE jumper open and connect
the clock input between SYNC test point and a GND test point. The device will operate in FPWM
when it is synchronized to an external clock.
SYNC —Test point to monitor the SYNC/MODE pin and external clock input
The SYNC test point can used to monitor the SYNC/MODE pin voltage on the device. It is also the
external clock input if synchronization is needed. Connect the external clock input to the SYNC test
point with the SYNC/MODE jumper open on all pins. The external clock frequency must be
between 350 kHz and 2.2 MHz if used. The device operates in FPWM when synchronized to a
clock.
VCC —Test point to monitor the VCC pin
This test point is to monitor the voltage at the VCC output.
Edge Connector —Additional connector to attach the EVM to a cable harness.
The edge connector provides the option of connecting the EVM to a cable harness if available. It
includes the power connections: VIN, GND, VOUT, and VIN-EMI. It also has Kelvin sense
connections for VIN (VIS), VOUT (VOS_P), and GND (VSNS-). See the schematic in Figure 4 for
all the signals connected to the edge connector.

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4 Schematic
The three variants of the EVM shown in Table 2 share the same schematic with component variants
shown in Section 6. The LM73605EVM_5V_400K Schematic is shown in Figure 4 as an example.
Figure 4. LM73605EVM_5V_400K Schematic

www.ti.com Board Layout
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5 Board Layout
Figure 5 through Figure 9 show the board layout for the LM7360xEVM. The EVM offers resistors,
capacitors, and test points to configure the output voltage, precision enable pin, set frequency and
external clock synchronization.
The 30-pin WQFN package offers an exposed thermal pad which must be soldered to the copper landing
on the PCB for optimal thermal performance. The PCB consists of a 4-layer design. There are 2-oz copper
planes on the top and bottom and 1-oz copper mid-layer planes to dissipate heat with an array of thermal
vias under the thermal pad to connect to all four layers.
Test points have been provided for ease of use to connect the power supply, required load and to monitor
critical signals. The 12-pin edge connector can also be used to facilitate the use of a cable harness if one
is required.
Figure 5. Top Layer and Silkscreen Layer

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Figure 6. Top Layer Routing
Figure 7. Mid-Layer 1 Ground Plane

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Figure 8. Mid-Layer 2 Routing
Figure 9. Bottom Layer Routing

Bill of Materials www.ti.com
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6 Bill of Materials
There are three sets of variants for the LM73605/LM73606 EVM, as shown in Table 2. The bills of
materials of the three variants are shown in Table 3,Table 4 and Table 5.
Table 3. LM73605EVM-5V-2MHz 5-A 2.2-MHz EVM Bill of Materials
Designator Comment Description Manufacture
rPart Number Quantity
C1, C8 CO, CI1 CAP, CERM, 0.47 µF, 50 V, +/- 10%, X7R,
0805 MuRata GRM21BR71H474KA88L 2
C2, C3 CO1, CO2 CAP, CERM, 22 µF, 16 V, +/- 10%, X7R,
1210 MuRata GRM32ER71C226KE18L 2
C7 CB CAP, CERM, 0.47uF, 25V, +/-10%, X5R,
0603 MuRata GRM188R61E474KA12D 1
C9 CI2 CAP, CERM, 10 µF, 50 V, +/- 10%, X7R,
1210 MuRata GRM32ER71H106KA12L 1
C16 CVCC CAP, CERM, 2.2uF, 10V, +/-10%, X6S,
0603 MuRata GRM188C81A225KE34D 1
L1 L Inductor, Shielded, Composite, 2.2 µH, 17.8
A, 0.01 ohm, SMD Coilcraft XAL7070-222MEB 1
R1 RINJ RES, 100, 1%, 0.125 W, 0805 Vishay-Dale CRCW0805100RFKEA 1
R2, R5 RFBT, RPG RES, 100 k, 1%, 0.1 W, 0603 Vishay-Dale CRCW0603100KFKEA 2
R3 RBIAS RES, 0, 5%, 0.1 W, 0603 Vishay-Dale CRCW06030000Z0EA 1
R4 RFBB RES, 24.9 k, 1%, 0.1 W, 0603 Vishay-Dale CRCW060324K9FKEA 1
R6 RT RES, 17.8 k, 1%, 0.1 W, 0603 Vishay-Dale CRCW060317K8FKEA 1
R8 RENT RES, 200 k, 1%, 0.125 W, 0805 Vishay-Dale CRCW0805200KFKEA 1
R9 RENB RES, 121 k, 1%, 0.125 W, 0805 Vishay-Dale CRCW0805121KFKEA 1
R10 RPU RES, 10.0 k, 1%, 0.1 W, 0603 Vishay-Dale CRCW060310K0FKEA 1
U1 LM73605RNPR 3.5V to 36V 5A Synchronous Step-Down
Voltage Regulator, RNP0030A (WQFN-30) Texas Instruments LM73605RNPR 1
C4, C5 CO3, CO4 CAP, CERM, 22 µF, 16 V, +/- 10%, X7R,
1210 MuRata GRM32ER71C226KE18L 0
C6 CO5 CAP, CERM, 0.47 µF, 50 V, +/- 10%, X7R,
0805 MuRata GRM21BR71H474KA88L 0
C10 CI3 CAP, CERM, 10 µF, 50 V, +/- 10%, X7R,
1210 MuRata GRM32ER71H106KA12L 0
C11, C12,
C13 C-FLT1, C-FLT2, C-FLT3 CAP, CERM, 2.2 µF, 50 V, +/- 10%, X5R, 1206 MuRata GRM31CR61H225KA88L 0
C14 CBULK CAP, AL, 100 µF, 63 V, +/- 20%, 0.35 ohm,
SMD Panasonic EEE-FK1J101P 0
C15 CFF CAP, CERM, 4.7 pF, 50 V, +/- 5%,
C0G/NP0, 0603 AVX 06035A4R7CAT2A 0
C17 CBIAS CAP, CERM, 1 µF, 25 V, +/- 10%, X7R,
0603 Kemet C0603C105K3RACTU 0
C18 CSS CAP, CERM, 0.01 µF, 100 V, +/- 20%, X7R,
0603 AVX 06031C103MAT2A 0
L2 L-IN Inductor, Shielded, Composite, 2.2uH,
12.9A, 0.0137 ohm, SMD Coilcraft XAL7030-222MEB 0
R7 RSYNC RES, 100, 1%, 0.1 W, 0603 Vishay-Dale CRCW0603100RFKEA 0