Texas Instruments LM73605 Manual de usuario

SNVU579–September 2017

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.

CSS

RSYNC

RENT

RENB

PVIN

PGND CBOOT

VCC

BIAS

AGND

VIN

COUT

CBOOT

CIN

CVCC

VOUT

RFBT

RFBB

SYNC/

MODE

SS/TRK PGOOD

VCC

BIAS

SS/TRK

423

PVIN

DAP PVIN

PGND

CBOOT

PGND

PGOOD

8AGND

SYNC/

MODE

29 28 27

13 14 15

SW PVIN

NC NC NC NC

Introduction

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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

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Quick Start

SNVU579–September 2017

LM73605 / LM73606 EVM User’s Guide

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

Detailed Descriptions

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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.

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Detailed Descriptions

SNVU579–September 2017

LM73605 / LM73606 EVM User’s Guide

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.

Schematic

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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

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Board Layout

SNVU579–September 2017

LM73605 / LM73606 EVM User’s Guide

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

Board Layout

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Figure 6. Top Layer Routing

Figure 7. Mid-Layer 1 Ground Plane

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Board Layout

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LM73605 / LM73606 EVM User’s Guide

Figure 8. Mid-Layer 2 Routing

Figure 9. Bottom Layer Routing

Bill of Materials

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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

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