Texas Instruments TPS92691 User manual

User's Guide
SLVUAL8–December 2015
TPS92691 SEPIC LED Driver Evaluation Board
This user's guide describes the characteristics, operation, and use of the TPS92691 SEPIC Evaluation
Module (EVM). A complete schematic diagram, printed-circuit board layouts, and bill of materials are
included in this document.
Contents
1 Introduction ................................................................................................................... 3
2 Description.................................................................................................................... 3
2.1 Typical Applications ................................................................................................ 3
2.2 Features.............................................................................................................. 3
3 Connector Description....................................................................................................... 4
3.1 J1, VIN, GND........................................................................................................ 4
3.2 J2, LED+, LED–..................................................................................................... 4
3.3 TP1, SHUTDOWN.................................................................................................. 4
3.4 TP2, SYNC .......................................................................................................... 4
3.5 TP3, PWM ........................................................................................................... 4
3.6 TP5, IADJ............................................................................................................ 5
3.7 TP4, IMON........................................................................................................... 5
4 Electrical Performance Specifications..................................................................................... 5
5 Schematic..................................................................................................................... 6
6 Performance Data and Typical Characteristic Curves.................................................................. 8
6.1 Efficiency............................................................................................................. 8
6.2 Line Regulation ..................................................................................................... 9
6.3 Load Regulation................................................................................................... 10
6.4 Temperature Characteristics..................................................................................... 11
6.5 Analog Adjust Settings............................................................................................ 12
6.6 PWM Dimming..................................................................................................... 13
6.7 Typical Waveforms................................................................................................ 14
6.8 EMI ................................................................................................................. 16
7 Optimizing EVM Performance Based on LED String Voltage and Current......................................... 17
8 TPS92691EVM-001 Assembly Drawing and PCB layout............................................................. 17
9 Bill of Materials ............................................................................................................. 19
List of Figures
1 Connection Diagram......................................................................................................... 4
2 TPS92691EVM-001 Schematic: Configured With a High-Side Current Sense and a High-Side Series
PFET Device ................................................................................................................. 6
3 Alternate Configuration With a Low-Side Current Sense and a Low-Side Series NFET Device.................. 7
4 Efficiency vs Input Voltage (Number of series connected LEDs = 3)................................................. 8
5 Efficiency vs. Input Voltage (Number of series connected LEDs = 7)................................................ 8
6 Efficiency vs. Input Voltage (Number of Series-Connected LEDs = 13) ............................................. 8
7 Output LED Current vs Input Voltage (VIADJ = 140 mV) ................................................................ 9
8 Output LED Current vs Input Voltage (VIADJ = 420 mV) ................................................................ 9
9 Output LED Current vs Input Voltage (VIADJ = 700 mV) ................................................................ 9
10 Output LED Current vs. LED String Configuration (VIADJ = 140 mV)................................................. 10
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11 Output LED Current vs. LED String Configuration (VIADJ = 420 mV)................................................. 10
12 Output LED Current vs. LED String Configuration (VIADJ = 700 mV)................................................. 10
13 LED Current Error vs. Ambient Temperature (VIN = 14 V, Number of LEDs in series = 3)...................... 11
14 LED Current Error vs. Ambient Temperature (VIN = 14 V, Number of LEDs in series = 7)...................... 11
15 LED Current Error vs. Ambient Temperature (VIN = 14 V, Number of LEDs in series = 13).................... 11
16 Circuit Configurations to Set Analog Adjust Reference Voltage ..................................................... 12
17 Output LED Current vs. IADJ Voltage, VIADJ (VIN = 14 V, Number of LEDs in Series = 3)....................... 13
18 Normalized LED Current vs. PWM Duty Cycle (VIADJ = 700 mV, Number of LEDs in series = 13).............. 13
19 Soft-Start Sequence ....................................................................................................... 14
20 Nominal Operation ......................................................................................................... 14
21 Over-Voltage Protection................................................................................................... 14
22 SYNC Operation............................................................................................................ 14
23 PWM Dimming (Duty Cycle = 50 %, Frequency = 240 Hz)........................................................... 14
24 PWM Dimming (Duty cycle = 50 %, Frequency = 240 Hz) ........................................................... 14
25 PWM Dimming (Duty cycle = 4%, Frequency = 240 Hz) ............................................................. 14
26 PWM Dimming (Duty cycle = 4%, Frequency = 240 Hz) ............................................................. 14
27 IMON Response to LED Open-Circuit Fault............................................................................ 14
28 IMON Response to LED Short-Circuit Fault............................................................................ 14
29 Start-Stop (Warm-Crank) Transient Response......................................................................... 15
30 Start-Stop (Warm-Crank)Transient Response.......................................................................... 16
31 Conducted EMI Based on CISPR 25 Class 3 Limits .................................................................. 16
32 Assembly Drawing ......................................................................................................... 17
33 Top Layer and Top Overlay (Top View)................................................................................. 18
34 Bottom Layer and Bottom Overlay (Bottom View) ..................................................................... 18
List of Tables
1 TPS92691EVM-001 Electrical Performance Specifications............................................................ 5
2 Bill of Materials ............................................................................................................. 19
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www.ti.com Introduction
1 Introduction
The TPS92691EVM-001 evaluation module (EVM) helps designers evaluate the operation and
performance of the TPS92691-Q1 and TPS92691, a multi-topology controller designed for automotive
lighting and general illumination applications. The TPS92691EVM-001 uses the TPS92691-Q1 ( AEC
Q100) IC; however, for general illumination and other non-automotive applications, the TPS92691 is
available in the same package and pin configuration and with identical performance characteristics. The
TPS92691-Q1 device implements fixed-frequency peak current mode control technique with
programmable switching frequency, slope compensation and startup timing. It incorporates a low offset
rail-to-rail current sense amplifier that can directly measure LED current over an output voltage range of 0
V to 65 V. Additional features include wide input voltage range (0 V to 65 V), PWM dimming capability,
analog dimming capability, adjustable/syncable switching frequency, input undervoltage protection, output
overvoltage protection and switch cycle-by-cycle current limit. The controller can be used to implement a
range of LED driver topologies including Boost, Buck-Boost (Boost-to-Battery), SEPIC, Cuk, and Flyback,
based on the output LED stack voltage.
2 Description
The TPS92691EVM-001 is a fully assembled and tested SEPIC LED driver designed to power a single
string of series-connected LEDs. Accurate closed-loop LED current regulation is achieved using a low-
offset current sense amplifier that is compatible with either high- or low-side current-sensing
implementations. The DC current set point can be varied over a 15:1 ratio using the high-impedance
analog adjust (IADJ) input. An integrated gate-driver circuit and proprietary PWM dimming logic is
incorporated to enable external series FET PWM dimming with greater than 100:1 dimming ratio.
LED short-circuit failure and other cable harness fault detection is facilitated by current monitor output
(IMON), which reports the instantaneous status of LED current measured by the rail-to-rail current sense
amplifier. The current monitor output is used in conjunction with microcontroller or discrete circuitry to
implement customized fault protection schemes.
2.1 Typical Applications
This converter design describes an application of the TPS92691-Q1 device as a SEPIC LED driver with
the specifications described in Table 1. For applications with a different input voltage range or different
output voltage range, refer to the TPS92691-Q1 datasheet.
2.2 Features
• Versatile LED driver capable of driving a string of 1 to 20 series-connected white LEDs
• Wide input voltage range (4.5 V to 40 V): Supports automotive start-stop and load dump transients (65
Vmax)
• Compatible with high- or low-side current sense resistor locations
• Simple microcontroller interface to set LED current reference and PWM duty cycle
• Integrated gate-drive circuit to enable series FET dimming
• Instantaneous current monitor output to facilitate LED fault detection and mitigation
• Supports Boost, Buck-Boost (Boost-to-Battery), SEPIC, Cuk, and Flyback LED driver topologies
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+
±
V
+
±
A
+
±
A
DC
Power
Supply Voltmeter
+
s
Function
Generator
Ammeter
Ammeter
Connector Description www.ti.com
3 Connector Description
This section describes the connectors and test points on the EVM and how to properly connect, setup,
and use the TPS92691EVM-001.
Figure 1. Connection Diagram
3.1 J1, VIN, GND
The screw-down connector, J1, marked VIN and GND is for connecting the EVM to the DC input voltage
supply. One other VIN and PGND test point is provided on the board that can also be used for all
purposes but input power.
3.2 J2, LED+, LED–
The screw-down connector, J2, marked LED+ and LED– is for connecting the LED load to the board. The
leads to the LED load should be twisted and kept as short as possible to minimize voltage drop,
inductance, and EMI transmission. This design is for approximately 1 to ≈20 white LEDs.
3.3 TP1, SHUTDOWN
The test point SHUTDOWN connects through a 1-kΩresistor to the SS pin of the TPS92691-Q1 device.
The voltage range is from 0 V to 5 V, if driven externally. The SS voltage can be monitored with this test
point. Pulling SHUTDOWN to GND will also serve to disable the part and put it into STANDBY mode.
3.4 TP2, SYNC
The SYNC test point is AC-coupled to the RT/SYNC pin of the TPS92691-Q1 device through a 100-pF
capacitor. Apply a square wave with pulse width greater than 200 ns and logic-low level of GND and a
high level between 3 V and 5 V to synchronize the switching frequency to the applied frequency. The
frequency range of SYNC is from 332 kHz to 449 kHz (±15%) for the nominal set point of 390-kHz
switching frequency.
3.5 TP3, PWM
The PWM test point connects through a 1-kΩresistor to the PWM pin of the TPS92691-Q1 device. Leave
open for normal operation. If PWM dimming is used, apply a square wave with a low level of GND and a
high level of between 3 V and 5 V. The dimming frequency range is 100 Hz to 1 kHz.
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3.6 TP5, IADJ
The IADJ test point connects through a two-pole low-pass filter to the IADJ pin of the TPS92691-Q1
device. The default reference is set to 420 mV through a resistor divider network connected to VCC
resulting in output current of 300 mA. The voltage on IADJ can be externally set using either a pulse width
modulated signal from function generator or a DC power supply between 140 mV to over 2.4 V. For more
details on setting analog adjust voltage refer to Section 6.5.
3.7 TP4, IMON
The IMON test point connects directly to the IMON pin of the TPS92691-Q1 device. The IMON voltage,
corresponding to measured LED current by integrated rail-to-rail current sense amplifier, can be monitored
with this test point. The pin can be connected to an external comparator or microcontroller to detect LED
short-circuit, LED+ to VIN, and LED+ to GND fault conditions.
4 Electrical Performance Specifications
Table 1. TPS92691EVM-001 Electrical Performance Specifications
Parameter Test Conditions MIN TYP MAX Unit
Input Characteristics
Input voltage range 7 14 40 V
Input UVLO setting 4.5 V
Maximum switch node voltage 100 V
Output Characteristics
Output voltage, VOUT LED+ to LED– 2 40 65 V
Output current 100 300 1700 mA
Maximum output power 25 W
Analog dimming range VIADJ = 140 mV to 2.4 V 17:1
PWM dimming range 240-Hz PWM frequency 100:1
Systems Characteristics
Efficiency Input voltage = 14 V, 13 LEDs, ILED = 90%
300 mA
Switching frequency 390 kHz
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Schematic www.ti.com
5 Schematic
Figure 2. TPS92691EVM-001 Schematic: Configured With a High-Side Current Sense and a High-Side Series PFET Device
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Figure 3. Alternate Configuration With a Low-Side Current Sense and a Low-Side Series NFET Device
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Input Voltage, VIN (V)
Efficiency (%)
5 10 15 20 25 30 35 40
70
80
90
100
D003
ILED = 100mA
ILED = 300mA
ILED = 500mA
Input Voltage, VIN (V)
Efficiency (%)
5 10 15 20 25 30 35 40
70
80
90
100
D002
ILED = 100mA
ILED = 300mA
ILED = 500mA
Input Voltage (V)
Efficiency (%)
5 10 15 20 25 30 35 40
70
80
90
100
D001
ILED = 100mA
ILED = 300mA
ILED = 500mA
ILED = 1.5A
Performance Data and Typical Characteristic Curves www.ti.com
6 Performance Data and Typical Characteristic Curves
The following performance curves are presented for the EVM configured with a high-side current sense
resistor and a series PFET device (Figure 2). The EVM circuit can be modified to implement low-side
current sense and series NFET dimming ( Figure 3), with minor differences in performance.
6.1 Efficiency
Figure 4. Efficiency vs Input Voltage (Number of series connected LEDs = 3)
Figure 5. Efficiency vs. Input Voltage (Number of series connected LEDs = 7)
Figure 6. Efficiency vs. Input Voltage (Number of Series-Connected LEDs = 13)
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Input Voltage, VIN (V)
LED Current (mA)
5 10 15 20 25 30 35 40
495
497
499
501
503
505
D006
LEDs =3
LEDs = 7
LEDs = 13
Input Voltage, VIN (V)
LED Current (mA)
5 10 15 20 25 30 35 40
299.25
299.5
299.75
300
300.25
300.5
300.75
301
301.25
D005
LEDs =3
LEDs = 7
LEDs = 13
Input Voltage, VIN (V)
LED Current (mA)
5 10 15 20 25 30 35 40
99
99.5
100
100.5
101
D004
LEDs =3
LEDs = 7
LEDs = 13
www.ti.com Performance Data and Typical Characteristic Curves
6.2 Line Regulation
Figure 7. Output LED Current vs Input Voltage (VIADJ = 140 mV)
Figure 8. Output LED Current vs Input Voltage (VIADJ = 420 mV)
Figure 9. Output LED Current vs Input Voltage (VIADJ = 700 mV)
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No. of LEDs in Series
LED Current (mA)
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
498
500
502
504
D009
VIN = 10V
VIN = 14V
VIN = 18V
No. of LEDs in Series
LED Current (mA)
2 4 6 8 10 12 14 16 18
298
299
300
301
302
303
304
D008
VIN = 10V
VIN = 14V
VIN = 18V
No. of LEDs in Series
LED Current (mA)
2 4 6 8 10 12 14 16 18
98
98.5
99
99.5
100
100.5
101
101.5
102
D007
VIN = 10V
VIN = 14V
VIN = 18V
Performance Data and Typical Characteristic Curves www.ti.com
6.3 Load Regulation
Figure 10. Output LED Current vs. LED String Configuration (VIADJ = 140 mV)
Figure 11. Output LED Current vs. LED String Configuration (VIADJ = 420 mV)
Figure 12. Output LED Current vs. LED String Configuration (VIADJ = 700 mV)
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