Texas Instruments TPS92518EVM User Manual

User's Guide

SLUUBM0–May 2017

TPS92518EVM Dual Buck Controller Evaluation Module

This user's guide describes the specifications, board connection description, characteristics, operation, and use of the combined, two board TPS92518 Evaluation Module (EVM). A complete schematic diagram, printed circuit board layouts, and bill of materials are included in this document.

Contents

1 Description.................................................................................................................... 2

2 Performance Specifications ................................................................................................ 3

3 Performance Data and Typical Characteristic Curves.................................................................. 4

4 Schematic, PCB Layout, and Bill of Materials.......................................................................... 11

5 Software ..................................................................................................................... 16

6 Use of LEDSPIMCUEVM-879 Microcontroller Board for SPI Communications with the TPS92518............ 22

List of Figures

1 Frequency vs Output Voltage.............................................................................................. 4

2 Efficiency Over Temperature at Different Peak Threshold Settings .................................................. 4

3 PWM Dimming, Multiple PWM Frequencies, Both Channels.......................................................... 5

4 Single-Channel PWM Dimming at 400 Hz ............................................................................... 5

5 SPI Setting Output Enable Bit and Subsequent Switching Initiation.................................................. 6

6 Hardware PWM Enable Pulled High, Triggering Switching ............................................................ 6

7 SPI Clearing Output Enable Bit and Subsequent Switching Shutdown .............................................. 7

8 Hardware PWM Enable Pulled Low, Triggering Chip Shutdown...................................................... 7

9 Current Sharing .............................................................................................................. 8

10 Switch Node Current ........................................................................................................ 8

11 Switch Node Current ........................................................................................................ 9

12 Additional Circuitry Required for Shunt FET Dimming ............................................................... 10

13 TPS92518EVM-878 Schematic .......................................................................................... 11

14 TPS92518EVM-878 Top Side ............................................................................................ 12

15 TPS92518EVM-878 Bottom Side ........................................................................................ 13

16 Setup Screen 1 ............................................................................................................. 16

17 Setup Screen 2 ............................................................................................................. 16

18 Setup Screen 3 ............................................................................................................. 17

19 Setup Screen 4 ............................................................................................................. 17

20 Setup Screen 5 ............................................................................................................. 18

21 Setup Screen 6 ............................................................................................................. 18

22 Setup Screen 7 ............................................................................................................. 19

23 Setup Screen 8 ............................................................................................................. 19

24 Setup Screen 9 ............................................................................................................. 20

25 Setup Screen 10 ........................................................................................................... 20

26 Setup Screen 11 ........................................................................................................... 20

27 LEDSPIMCUEVM-879 Schematic, Page 1............................................................................. 22

28 LEDSPIMCUEVM-879 Schematic, Page 2............................................................................. 23

29 LEDSPIMCUEVM-879 Schematic, Page 3............................................................................. 24

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Description

30 LEDSPIMCUEVM-879 Schematic, Page 4 ............................................................................. 25

List of Tables

1 Connector Descriptions ..................................................................................................... 2

2 Test Points.................................................................................................................... 3

3 TPS92518 EVM Performance Specifications............................................................................ 3

4 TPS92518EVM-878 Bill of Materials..................................................................................... 14

Trademarks

Microsoft, .NET Framework are registered trademarks of Microsoft Corporation. All other trademarks are the property of their respective owners.

1 Description

The complete two-board TPS92518EVM solution provides a dual-channel, high-brightness LED current regulator which is configurable via a graphical user interface (GUI). It is designed to operate with an input voltage in the range of 6.5–65 V. The EVM is setup for default output currents of 538 mA per channel, easily adjustable to different currents up to 1.65 A, for an LED stack between approximately 3 V to nearly 65 V. The TPS92518 provides high efficiency, high bandwidth, fast PWM dimming, SPI dimming, and adjustable on-time.

1.1 Typical Applications

This manual outlines the operation and implementation of the TPS92518 as a dual-channel LED current regulator with the specifications listed in Table 1. For applications with a different input voltage range or different output voltage range, refer to the TPS92518 data sheet (SLUSCR7). The TPS92518EVM-878 evaluation board is designed to be controlled by a TI microcontroller board, part number LEDSPIMCUEVM-879, available separately, although it can be controlled by any SPI-capable control system. Note that the TPS92518x supports a means to enable the part without SPI communication. By applying a voltage above the second threshold level, 23.6 V typical, on the ENABLE pin, the state of the LEDxEN register is bypassed. This allows a TPS92518 to be powered and operated using the default register values (for details, refer to the TPS92518 data sheet (SLUSCR7)).

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1.2 Connector Description

Table 1 describes the connectors and Table 2 lists the test points on the EVM and how to properly

connect, set up, and use the TPS92518EVM-878.

Table 1. Connector Descriptions

Connector Label Description

J1 connects power to channel 1 of the board, and J18 connects power to channel 2.

J1 and J18 VIN, GND

J2 and J3 LED+, LED– and GND

J4 SPI control header

J10 and J11

J12 and J14

SPI control from an

LEDSPIMCUEVM-879

controller board

SPI MISO pullup resistor

jumpers

The evaluation board is set up with both channel supplies connected through R15, so power connection can be to either J1 or J18 to power both channels from a single supply. The board silkscreen identifies power (one pin) and ground (two pins) connections on each connector.

J2 connects the channel 1 output to the LED load, and J3 connects the channel 2 output to a separate LED load. The leads to the LED load should be twisted and kept short to minimize voltage drop, inductance, and EMI. The board silkscreen identifies LED+ and LED– and GND.

J4 allows attachment of a header cable for SPI control of the chip. The board silkscreen identifies GND, MISO, MOSI, SCK, and SSN.

J10 and J11 allow daisy-chaining TPS92518EVM-878 boards to each other with one LEDSPIMCUEVM-879 control board attached to the left-hand side of the left-most evaluation board for controlling the TPS92518. This interface allows control of the chip hardware enable line, PWM inputs to both channels, SPI lines, and hardware address lines for multiple SSN settings for systems that have multiple TPS92518EVM-878 boards controlled by a single LEDSPIMCUEVM-879 controller interface board.

J12 and J14 provide for two different values of pullup resistor to the MISO line, 2.2 kΩ and 4.7 kΩ provided on the evaluation board.

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Performance Specifications

Table 1. Connector Descriptions (continued)

Connector Label Description

J13 and J15 are jumpers provided to allow for PWM signals to the two channels to

J13 and J15 PWM jumpers

J8 MISO

J7 SPI DI out

J10 Control connector

SSN configuration

jumper

be generated from an LEDSPIMCUEVM-879 (when populated) or applied from an external source (when jumper is removed and the signal is connected to pin 1 one of the connector). J13 provides PWM to channel 1 of the chip, while J15 provides PWM to channel 2.

J9 allows configuration of the SSN chip select line for use with multiple chips on the same SPI bus.

This jumper enables configurations: shorting pins 5–6 sets the SPI communication architecture up for a single TPS92518 or the end point of a daisy chain of them, shorting 1–2 and 5–6 sets up for a TPS92518 in the middle of a daisy-chain, and shorting 3–4 and 5–6 provides for a star architecture.

If this jumper is closed, it allows multiple TPS92518 devices to be connected in a star configuration.

This connector allows the TPS92518 board to attach to a microcontroller, such as the LEDSPIMCUEVM-879.

Table 2. Test Points

Test Point Description

Metal turrets All metal turrets are grounds.

PWM1 and PWM2 The test points labeled PWM1 and PWM2 allow for external signal sources to control the TPS92518

ENABLE The test point labeled ENABLE near J10 allows for an external enable signal to control switching of

VDIGI The VDIGI test point allows for external application of power to the MISO pull-up resistors or

SW1 and SW2 The SW1 and SW2 test points provide locations to monitor the switch nodes of the two channels.

VIN The VIN test point allows for external application of power to the digital system of the chip

hardware PWM dimming.

the TPS92518.

monitoring of the pull-up voltage.

independent of the analog power supplies to either channel 1 or 2. On the evaluation board this is shorted to the analog supply by R16, so separate application of power is neither necessary nor useful without removal of R16.

2 Performance Specifications

Table 3. TPS92518 EVM Performance Specifications

Parameter Test Conditions Min Typ Max Units

Input Characteristics

Voltage 6.5 14 65 V Maximum Input

Current

Output Characteristics

Output Voltage, V

LED

Output Current, I

LED

Dimming Methods

Analog LEDx_PKTH_DAC register = 0 to 255 yes PWM Use PWMx pin input yes

Shunt FET

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Output/LED Voltage (absolute maximum) 0 65 Output/LED Voltage (practical limit) 60 Output current 0 1.65 Default Output Current (Registers = 127/255) 0.538

Use external FET, program LEDx_MAXOFF_DAC register as per datasheet outline

TPS92518EVM Dual Buck Controller Evaluation Module

2.5 A

yes

Temperature (qC)

Efficiency (%)

Output Current (Amps)

-60 -40 -20 0 20 40 60 80 100 120 140 160

94 0.8

94.1 0.81

94.2 0.82

94.3 0.83

94.4 0.84

94.5 0.85

94.6 0.86

94.7 0.87

94.8 0.88

94.9 0.89

95 0.9

D001

Efficiency ILED1 ILED2

Output Voltage (V)

Switching Frequency (Hz)

0 5 10 15 20 25 30 35 40 45 50 55

150000

200000

250000

300000

350000

400000

450000

500000

550000

600000

650000

700000

750000

800000

850000

900000

Performance Data and Typical Characteristic Curves

Table 3. TPS92518 EVM Performance Specifications (continued)

Parameter Test Conditions Min Typ Max Units

Systems Characteristics

Switching frequency

Switching Frequency (fSW) Range 1 2000 kHz

Peak efficiency 95 % Operating

temperature

3 Performance Data and Typical Characteristic Curves

Figure 1 through Figure 4 illustrate the performance data and typical characteristic curves.

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–40 25 125 ºC

Conditions: VIN50 V, peak threshold = 50, minimum off-time = 127

Conditions:IN50 V, V

Figure 2. Efficiency Over Temperature at Different Peak Threshold Settings

TPS92518EVM Dual Buck Controller Evaluation Module

24.7 V, peak threshold = 120, minimum off-time = 127

LED

Figure 1. Frequency vs Output Voltage

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Dutycycle (%)

Output Current (A)

0 10 20 30 40 50 60 70 80 90 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5 Ch. 2, PWMfreq=400Hz

Dutycycle (%)

Output Current (A)

0 10 20 30 40 50 60 70 80 90 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5 Ch. 1 PWMfreq=250Hz Ch. 2 PWMfreq=250Hz Ch. 1 PWMfreq= 400Hz Ch. 2 PWMfreq=400Hz Ch. 1 PWMfreq=600Hz Ch. 2 PWMfreq=600Hz Ch. 1 PWMfreq=1000Hz Ch. 2 PWMfreq=1000Hz

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Performance Data and Typical Characteristic Curves

VIN12 V, V

3 V, peak threshold = 127, off time = 127

LED

Figure 3. PWM Dimming, Multiple PWM Frequencies, Both Channels

3 V, peak threshold = 127, off time = 127

LED

Figure 4. Single-Channel PWM Dimming at 400 Hz

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Performance Data and Typical Characteristic Curves

3.1 Startup Waveforms

3.1.1 Startup After SPI Enable Command

Figure 5. SPI Setting Output Enable Bit and Subsequent Switching Initiation

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3.1.2 Startup on Hardware Enable Pin Transition

Figure 6. Hardware PWM Enable Pulled High, Triggering Switching

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3.2 Shutdown Waveforms

3.2.1 Shutdown After SPI Disable

Figure 7. SPI Clearing Output Enable Bit and Subsequent Switching Shutdown

Performance Data and Typical Characteristic Curves

3.2.2 Shutdown After Hardware Enable Pin Transition

Figure 8. Hardware PWM Enable Pulled Low, Triggering Chip Shutdown

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Performance Data and Typical Characteristic Curves

3.3 Current Sharing

The TPS92518 device can be set up to share current with both channels driving a single load.

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VIN= 65 V, driving 1 LED for a V current, showing max and mean inductor currents on channels 1 and 2

of 3.0062 V, with a peak threshold = 45 to get approximately a 225-mA LED

LED

Figure 9. Current Sharing

3.4 Diode and Boot Capacitor Current

3.4.1 Diode, Inductor, and Boot Capacitor Current at Low Output Current

Showing inductor current into the LED and current flow through the catch diode and boot capacitor used for supplying gate drive power. VIN= 65 V, V

TPS92518EVM Dual Buck Controller Evaluation Module

= 23 V, T

LED

OFF

Figure 10. Switch Node Current

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Performance Data and Typical Characteristic Curves

3.4.2 Diode, Inductor, and Boot Capacitor Current at High Output Current

Showing inductor current into the LED and current flow through the catch diode and boot capacitor used for supplying gate drive power. VIN= 65 V, V

= 23 V, T

LED

OFF

Figure 11. Switch Node Current

3.4.3 Shunt FET Dimming

Shunt FET dimming is simple with the TPS92518. Short leads between the evaluation board and the LED load boards are important to prevent V board also helps to reduce V

overshoot. Adding an appropriately rated diode from the LED+ line that

LED

overshoot. Locating the shunt FET on or near the LED load

LED

conducts back to the positive VINinput will clamp voltage overshoot.

NOTE: There is no provision for mounting such a diode on the board: it must be soldered into the

wiring used to connect the shunt FET into the circuit.

Similarly, repopulating R17 and C21 with different values will also protect the V

pin from overshoots.

LED

Figure 12 illustrates the circuitry modifications for shunt FET dimming: increasing the size of R17, adding

a diode to VIN, and adding an appropriately-rated FET with a gate pulldown resistor. Either adding a diode or increasing R17 should be adequate. While the modified schematic shows both output capacitors removed, replacing one with a 220-pF capacitor rather than just removing both may give better V overshoot performance.

LED

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TPS92518EVM Dual Buck Controller Evaluation Module

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Texas Instruments TPS92518EVM User Manual

Specifications and Main Features

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