Texas Instruments AN-1870 LM26420 Manuale utente

User's Guide

SNVA353B–February 2009–Revised April 2013

AN-1870 LM26420 Evaluation Board

1 Introduction

The LM26420 evaluation board was designed to provide two 2A outputs, VOUT1 and VOUT2 . It is available in

either the HTSSOP package option of the LM26420 for easier probing or the WQFN version for evaluating

the smaller package. The design emphasizes on the compactness of the LM26420 PCB layout and is

thermally optimized. The total solution size is less than 35mm by 40mm. The board supports the

conversion from an input voltage ranging from 3V to 5.5V down to output voltages of 0.8V for each

channel. VOUT1 and VOUT2 are set to 1.2V and 2.5V respectively. The feedback resistor can be changed to

support output voltages as low as 0.8V or as high at 4.5V, assuming VIN is high enough to support it. The

EN pins are pulled up to VIN by jumpers for easy evaluation but can also be easily controlled by external

logic.

The board’s specifications are:

• Input Voltage: 3V to 5.5V

• Output Voltages: 1.2VOUT1 and 2.5VOUT2

• Maximum load current: 2A/output

• Minimum load current: 0A

• Size: 1.35 in. × 1.6 in.

• Peak Current Limit: ≊3.2A at 25°C

• Nominal Switching Frequency: 550 kHz or 2.2MHz

2 Powering Up the Board

Since the EN pins are directly tied to the input voltage via jumpers J1and J2, starting up the board is as

simple as connecting a voltage supply from 3V to 5.5V between the VIN and GND terminals. There should

be 1.2V on VOUT1 and 2.5V on VOUT2, assuming the jumpers connect VIN to EN for each channel. Great

care should be taken in powering up the supplies such that the input voltage, VIN, does not exceed the

Absolute Maximum Rating of 7V. If the part experiences voltages greater than 7V for a prolonged period

of time, then damage to the part can occur and then the evaluation board may cease working.

The linear soft-start ramps for the two output voltages and should last about 600 µs. Load can be applied

prior to power-up. If an output is shorted either before or after start-up, removal of the short-circuit

condition should bring the corresponding output back to normal voltage.

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SNVA353B–February 2009–Revised April 2013 AN-1870 LM26420 Evaluation Board

Typical Application Circuit

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3 Typical Application Circuit

Figure 1. LM26420 Demo Board Schematic

2AN-1870 LM26420 Evaluation Board SNVA353B–February 2009–Revised April 2013

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16-Pin WQFN Pin Out

4 16-Pin WQFN Pin Out

Figure 2. 16-Pin WQFN (top view)

Table 1. Pin Descriptions 16-Pin WQFN

Pin Name Function

1,2 VIND1Power Input supply for Buck1.

11, 12 VIND2Power Input supply for Buck2.

15 VINC Power Input supply for control circuitry.

4 PGND1Power ground pin for Buck 1.

9 PGND2Power ground pin for Buck 2.

14 AGND Signal ground pin. Place the bottom resistor of the feedback network as close as possible to pin.

6 PG1Power Good Indicator for Buck 1. Pin is connected through a resistor to an external supply (open

collector output).

7 PG2Power Good Indicator for Buck 2. Pin is connected through a resistor to an external supply (open

collector output).

5 FB1Feedback pin for Buck 1. Connect to external resistor divider to set output voltage.

8 FB2Feedback pin for Buck 2. Connect to external resistor divider to set output voltage.

3 SW1Output switch for Buck 1. Connect to the inductor.

10 SW2Output switch for Buck 2. Connect to the inductor.

16 EN1Enable control input. Logic high enable operation for Buck 1. Do not allow this pin to float or be

greater than VIN + 0.3V.

13 EN2Enable control input. Logic high enable operation for Buck 2. Do not allow this pin to float or be

greater than VIN + 0.3V.

DAP Die Attach Pad Connect to system ground for low thermal impedance and as a primary electrical GND

connection.

SNVA353B–February 2009–Revised April 2013 AN-1870 LM26420 Evaluation Board

20-Pin HTSSOP Pin Out

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5 20-Pin HTSSOP Pin Out

Figure 3. 20-Pin HTSSOP (top view)

Table 2. Pin Descriptions 20-Pin HTSSOP

Pin Name Function

3, 4 VIND1Power Input supply for Buck1.

17, 18 VIND2Power Input supply for Buck2.

1 VINC Power Input supply for control circuitry.

6,7 PGND1Power ground pin for Buck 1.

14, 15 PGND2Power ground pin for Buck 2.

20 AGND Signal ground pin. Place the bottom resistor of the feedback network as close as possible to pin.

9 PG1Power Good Indicator for Buck 1. Pin is connected through a resistor to an external supply (open

drain output).

12 PG2Power Good Indicator for Buck 2. Pin is connected through a resistor to an external supply (open

drain output).

8 FB1Feedback pin for Buck 1. Connect to external resistor divider to set output voltage.

13 FB2Feedback pin for Buck 2. Connect to external resistor divider to set output voltage.

5 SW1Output switch for Buck 1. Connect to the inductor.

16 SW2Output switch for Buck 2. Connect to the inductor.

2 EN1Enable control input. Logic high enable operation for Buck 1. Do not allow this pin to float or be

greater than VIN + 0.3V.

19 EN2Enable control input. Logic high enable operation for Buck 2. Do not allow this pin to float or be

greater than VIN + 0.3V.

10,11 NC No Connect.

DAP Die Attach Pad Connect to system ground for low thermal impedance, but it cannot be used as a primary GND

connection.

4AN-1870 LM26420 Evaluation Board SNVA353B–February 2009–Revised April 2013

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Schematic - X Version

6 Schematic - X Version

Figure 4. Schematic - X Version

Table 3. Bill of Materials - X Version

Item Designator Description Manufacturer Part No. Qty.

C1, C2, C3,

1 22µF, 6.3V, X5R, 1206 TDK C3216X5R0J226(M or K) 6

C4, C6, C7

2 C5 0.47µF, 16V, X7R, 0603 TDK C2012X7R1C474K 1

SPM6530T-1R0M120 or

3 L1, L2 1µH, 6.4A TDK 2

RLF7030T-1R0N6R4

4 R1 5.1k, 1%, 603 Vishay CRCW06035K10F 1

5 R2 21.3k, 1%, 603 Vishay CRCW060321K3F 1

6 R7, R8 49.9k, 1%, 603 Vishay CRCW060349K9F 2

R3, R4, R5,

7 10k, 1%, 603 Vishay CRCW060310K0F 4

8 R9 5.1 Ohm, 1%, 805 Vishay CRCW06035R10F 1

9 J1, J2 Jumper for Enables Sullins Connector Solutions STC02SYAN 2

0.094" Diameter Solder

10 TP1-TP8 Keystone Electronics 5011 8

Terminal

Dual 2A, 2.2MHz PWM

11 U1 Switcher, HTSSOP-20 or Texas Instruments LM26420 or LM26420 1

WQFN-16

SNVA353B–February 2009–Revised April 2013 AN-1870 LM26420 Evaluation Board

Schematic - Y Version

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7 Schematic - Y Version

Figure 5. Schematic - Y Version

Table 4. Bill of Materials - Y Version

Item Designator Description Manufacturer Part No. Qty.

C1, C2, C3,

1 22µF, 6.3V, X5R, 1206 TDK C3216X5R0J226(M or K) 6

C4, C6, C7

2 C5 0.47µF, 16V, X7R, 0603 TDK TMK105BJ104KV-F 1

RLF7030T-3R3M4R1 or

3 L1, L2 3.3µH, 6.4A TDK or Coilcraft 2

MSS7341-332NL_

4 R1 5.1k, 1%, 603 Vishay CRCW06035K10F 1

5 R2 21.3k, 1%, 603 Vishay CRCW060321K3F 1

6 R7, R8 49.9k, 1%, 603 Vishay CRCW060349K9F 2

R3, R4, R5,

7 10k, 1%, 603 Vishay CRCW060310K0F 4

8 R9 5.1 Ohm, 1%, 805 Vishay CRCW06035R10F 1

9 J1, J2 Jumper for Enables Sullins Connector Solutions STC02SYAN 2

0.094" Diameter Solder

10 TP1-TP8 Keystone Electronics 5011 8

Terminal

Dual 2A, 550kHz PWM LM26420YMH or

11 U1 Switcher, HTSSOP-20 or Texas Instruments 1

LM26420YSQ

WQFN-16

6AN-1870 LM26420 Evaluation Board SNVA353B–February 2009–Revised April 2013

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HTSSOP-20 PCB Layout

8 HTSSOP-20 PCB Layout

HTSSOP - Top Layer HTSSOP - Layer 2

HTSSOP - Layer 3 HTSSOP - Bottom Layer

SNVA353B–February 2009–Revised April 2013 AN-1870 LM26420 Evaluation Board

WQFN-16 PCB Layout

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9 WQFN-16 PCB Layout

WQFN - Top Layer WQFN - Layer 2

WQFN - Layer 3 WQFN - Bottom Layer

8AN-1870 LM26420 Evaluation Board SNVA353B–February 2009–Revised April 2013

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Typical Performance Characteristics

10 Typical Performance Characteristics

Efficiency - 1.2VOUT - X Version Efficiency - 2.5VOUT - X Version

Efficiency - 1.2VOUT - Y Version Efficiency - 2.5VOUT - Y Version

Load Step Response - X Version Load Step Response - Y Version

SNVA353B–February 2009–Revised April 2013 AN-1870 LM26420 Evaluation Board

Typical Performance Characteristics

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Steady State Operation - Y Version Enable

Start-up - VIN Applied

10 AN-1870 LM26420 Evaluation Board SNVA353B–February 2009–Revised April 2013

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