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TPS92511
SNVS901A – MARCH 2014 – REVISED MAY 2014
TPS92511 500-mA, 65-V Common Anode Constant Current Buck LED Driver Without
External Current Sensing Resistor
1 Features
3 Description
•
•
•
•
•
•
•
•
•
•
•
•
The TPS92511 is an easy to use 65V constant
current buck converter for driving a single LED string
with current up to 0.5A and efficiency up to 95%.
Only 5 external components are required for basic
operation and single layer PCB layout is feasible
because of the integration of a N-MOSFET, no
external current sensing resistor, no external
compensation and the proper terminal assignment. A
high-value external resistor programs the LED current
so that fine tuning of the LED current can be
achieved.
Another high-value external resistor
programs a constant switching frequency from 50kHz
to 500kHz. EMI design becomes easier as a result of
constant switching frequency.
The TPS92511
provides a wide input voltage range from 4.5V to
65V. By adding simple external circuits, the device
can handle applications with even higher input
voltages.
1
•
•
•
•
•
Wide Input Voltage Range: 4.5 V to 65 V
Requires NO External Current Sensing Resistor
Requires NO External Loop Compensation
Ease of Use, Needs Minimum 5 Components
1000:1 Contrast Ratio Feasible
Single Layer PCB Feasible
Can Work as High Voltage Buck Regulators
Can Work as Linear Current Shunt Regulators
Integrated Low-side N-channel MOSFET
LED Current Programmable up to 0.5 A
Typically ±3.6% LED Current Accuracy
Switching Frequency Programmable From 50 kHz
to 500 kHz
Current Limit Protection
VCC Under-voltage Lock-out
Thermal Shutdown Protection
Support Analog Dimming and Thermal Foldback
Power Enhanced SOIC-8 Exposed Thermal Pad
Package (HSOP-8)
2 Applications
•
•
•
•
•
High Power LED Driver
Architectural Lighting
Office Troffer
Automotive Lighting
MR-16 LED Lamp
The TPS92511 has very fast PWM dimming response
time. For example, if the switching frequency is 500
kHz, the minimum DIM pulse width is 6µs and the
dimming frequency is 150Hz, a contrast ratio of more
than 1000:1 can be achieved.
Simplified Application
VIN
TPS92511
VCC
CVCC
PGND
IADJ
RIADJ
VIN
LX
LED string
D1
DIM
FS
The TPS92511 is available in the Power Enhanced
SOIC-8 exposed thermal pad package.
ILED
L1
PWM dimming signal
GND
The TPS92511 employs a proprietary control scheme
to regulate the LED current without the need of
sensing the LED current directly. It applies a floating
buck topology with a low-side N-channel power
MOSFET, which does not need boot-strapping
capacitor. For multiple channel systems, the floating
buck topology together with the proprietary control
scheme allows a common-anode connection of the
LED strings without an external current sensing
network. This significantly reduces the number of
wiring and as well as overall manufacturing cost.
Device Information(1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
TPS92511
HSOP (8)
4.89mm × 3.90mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
RFS
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
TPS92511
SNVS901A – MARCH 2014 – REVISED MAY 2014
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
4
5
6
Absolute Maximum Ratings .....................................
Handling Ratings.......................................................
Recommended Operating Conditions ......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
7.3 Feature Description................................................. 10
7.4 Device Functional Modes........................................ 17
8
Application and Implementation ........................ 18
8.1 Application Information............................................ 18
8.2 Typical Application .................................................. 18
9 Power Supply Recommendation ........................ 21
10 Layout................................................................... 22
10.1 Layout Guidelines ................................................. 22
10.2 Layout Example .................................................... 22
11 Device and Documentation Support ................. 23
Detailed Description .............................................. 8
11.1 Trademarks ........................................................... 23
11.2 Electrostatic Discharge Caution ............................ 23
11.3 Glossary ................................................................ 23
7.1 Overview ................................................................... 8
7.2 Functional Block Diagram ......................................... 9
12 Mechanical, Packaging, and Orderable
Information ........................................................... 23
4 Revision History
Changes from Original (March 2014) to Revision A
Page
•
Corrected figure number sequencing ..................................................................................................................................... 1
•
Updated the Device Information Table .................................................................................................................................. 1
•
Changed Terminal to Pin........................................................................................................................................................ 3
2
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5 Pin Configuration and Functions
DDA (SO THERMAL PAD) PACKAGE
8 PINS
(TOP VIEW)
VCC
1
8
VIN
PGND
2
7
LX
IADJ
3
6
DIM
GND
4
5
FS
Pin Functions
PIN
DESCRIPTION
NAME
NO.
DIM
6
PWM Dimming Control. Apply logic level PWM signal to this pin dims the LED string. This pin is internally pulled up.
FS
5
Switching Frequency Setting. An external resistor RFS connecting the FS pin to ground programs the switching
frequency from 50 kHz to 500 kHz.
GND
4
Analog Signal Ground.
IADJ
3
Average LED Current Setting. An external resistor RIADJ connecting the IADJ pin to ground programs the average
LED current.
LX
7
Integrated MOSFET Drain. Internally connected to the drain of the integrated MOSFET. Connect this pin to the
output inductor and anode of the Schottky diode.
PGND
2
Power Ground. Must be connected to the GND pin for normal operation. The PGND and GND pins are not internally
shorted.
VCC
1
Internal Regulator Output. Typically regulated to 5.4 V. Connect a capacitor of larger than 1 µF between the VCC
and GND pins.
VIN
8
Input Voltage. Supply pin to the device. The input voltage range is from 4.5 V to 65 V.
Thermal pad
Thermal Connection Pad. Connect to a ground plane for heat dissipation.
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SNVS901A – MARCH 2014 – REVISED MAY 2014
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6 Specifications
6.1 Absolute Maximum Ratings
(1)
Unless otherwise specified, TJ = TA = 25°C
MIN
Pin voltage range
Temperature range
(1)
NOM
MAX
UNIT
VIN to GND
–0.3
65
V
VIN to GND (Transient)
–0.3
67
V
LX to PGND
–0.3
65
V
–3(2ns)
67
V
FS, IADJ to GND
–0.3
5
V
DIM to GND
–0.3
6
V
VCC to GND
–0.3
7
V
Operating junction temperature range, TJ
–40
Internally
limited
°C
LX to PGND (Transient)
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For specified specifications and test conditions, see the Electrical Characteristics.
6.2 Handling Ratings
Tstg
Storage temperature range
VESD
(1)
Human Body Model (HBM) ESD stress voltage
MIN
MAX
-65
150
°C
1.5
kV
1.5
kV
(2)
Charged Device Model (CDM) ESD stress voltage (3)
(1)
(2)
(3)
UNIT
Electrostatic discharge (ESD) to measure device sensitivity and immunity to damage caused by assembly line electrostatic discharges in
to the device.
Level listed above is the passing level per ANSI, ESDA, and JEDEC JS-001. JEDEC document JEP155 states that 500-V HBM allows
safe manufacturing with a standard ESD control process.
Level listed above is the passing level per EIA-JEDEC JESD22-C101. JEDEC document JEP157 states that 250-V CDM allows safe
manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
MIN
NOM
MAX
UNIT
VIN
Supply voltage range
4.5
65
V
TA
Operating free air temperature
–40
125
°C
TJ
Operating junction temperature
-40
125
°C
6.4 Thermal Information
TPS92511
THERMAL METRIC
(1)
DDA
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
59.9
RθJCtop
Junction-to-case (top) thermal resistance
59.1
RθJB
Junction-to-board thermal resistance
30.6
ψJT
Junction-to-top characterization parameter
11.0
ψJB
Junction-to-board characterization parameter
30.5
RθJCbot
Junction-to-case (bottom) thermal resistance
4.2
(1)
4
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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6.5 Electrical Characteristics
Unless otherwise specified, -40°C ≤ TJ = TA ≤ 125°C, VIN = 48 V
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
SYSTEM
IIN-DIM-HIGH
VIN Operating Current
4.5 V ≤ VIN ≤ 65 V, RIADJ = 3 kΩ, VDIM = High
2.8
3.15
mA
IIN-DIM-LOW
VIN Standby Current
4.5 V ≤ VIN ≤ 65 V, RIADJ = 3 kΩ, VDIM = Low
2.3
2.7
mA
ILX-OFF
LX Pin Current
Main switch turned OFF, VLX = VIN = 65 V
0.1
1.0
µA
ILED
Average LED Current
VFS = 4.6V, RIADJ = 3 kΩ, TA = 25°C
484
502
520
mA
VFS = 4.6V, RIADJ = 3 kΩ
477
502
528
mA
VFS = 4.6V, RIADJ = 6 kΩ, TA = 25°C
236
249
262
mA
VFS = 4.6V, RIADJ = 6 kΩ
233
249
268
mA
VFS = 4.6V, RIADJ = 10 kΩ, TA = 25°C
138
149
160
mA
VFS = 4.6V, RIADJ = 10 kΩ
133
149
166
mA
VIADJ
IADJ Pin voltage
1.224
1.25
1.278
V
VDIM-ON
DIM Pin Upper Threshold
VDIM Increasing
0.85
1.0
1.25
V
VDIM-OFF
DIM Pin Lower Threshold
VDIM Decreasing
0.44
VDIM-HYS
DIM Pin Threshold Hysteresis
fSW
Switching frequency
ton(min)
Minimum On-time
V
325
RFS = 20 kΩ
450
mV
500
550
kHz
250
400
ns
6.0
V
INTERNAL REGULATOR
VCC
VCC Regulated Output Voltage
CVCC =1 µF, no load
4.7
5.4
CVCC =1 µF, VIN = 4.5V, 2 mA load
3.7
4.1
3.75
VCC-UVLO-ON
VCC UVLO Upper Threshold
VCC rising
3.50
VCC-UVLO-OFF
VCC UVLO Lower Threshold
VCC falling
3.05
VCC-UVLO-HYS
VCC UVLO Hysteresis
V
4.00
V
V
275
mV
INTEGRATED MOSFET
RLX
Resistance Across LX and GND
Main Switch Turned ON, TA = 25°C
1.4
2.15
Ω
THERMAL SHUTDOWN
TSD
Thermal shutdown temperature
TJ Rising
165
TSD-HYS
Thermal shutdown hysteresis
TJ Falling
10
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5
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6.6 Typical Characteristics
Unless otherwise specified, all curves are taken at VIN = 48V with configuration in the application circuit for driving 12 LEDs
with ILED = 0.5A and fSW = 300 kHz as shown in this datasheet, and TA = 25°C.
3
6
LED string open
5
2.8
VCC (V)
IIN (mA)
4
2.6
2.4
3
2
2.2
VCC externally loaded
DIM pin open, LED string open
1
DIM = High
DIM = Low
2
0
0
10
20
30
40
50
60
70
0
4
VIN (V)
8
12
C001
C003
Figure 2. VCC vs IVCC
1.265
5.5
1.26
VIADJ (V)
VCC (V)
Figure 1. IIN vs VIN
6
5
1.255
VCC not loaded externally
DIM pin open, LED string open
4.5
1.25
4
1.245
0
10
20
30
40
50
60
70
-50
0
VIN (V)
50
100
C008
Figure 3. VCC vs VIN
Figure 4. VIADJ vs Temperature
1.8
510
Switching Frequence (kHz)
1.7
1.6
RLX (:)
150
Temperature (ºC)
C002
1.5
1.4
1.3
1.2
505
500
495
490
±50
0
50
100
150
Temperature (ºC)
±50
0
50
100
150
Temperature (ºC)
C009
Figure 5. RLX vs Temperature
6
16
IVCC (mA)
C010
Figure 6. fSW vs Temperature
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Typical Characteristics (continued)
505.0
252.5
504.0
252.0
503.0
251.5
502.0
251.0
501.0
250.5
ILED (mA)
ILED (mA)
Unless otherwise specified, all curves are taken at VIN = 48V with configuration in the application circuit for driving 12 LEDs
with ILED = 0.5A and fSW = 300 kHz as shown in this datasheet, and TA = 25°C.
500.0
499.0
250.0
249.5
498.0
249.0
497.0
248.5
496.0
248.0
495.0
247.5
0
±50
50
100
150
0
±50
Temperature (ºC)
50
100
150
Temperature (ºC)
C011
C012
Figure 7. ILED at 500 mA vs Temperature
Figure 8. ILED at 250 mA vs Temperature
151.5
0.16
151.2
0.14
150.9
0.12
0.1
150.3
IIN (A)
ILED (mA)
150.6
150.0
149.7
0.08
0.06
149.4
0.04
149.1
0.02
148.8
0
148.5
0
±50
50
100
0
150
10
20
30
Temperature (ºC)
40
50
60
70
VIN (V)
C014
C013
Figure 10. IIN vs VIN at LED Short
500
5
400
4
300
3
ILED (mA)
ILED (mA)
Figure 9. ILED at 150 mA vs Temperature
200
100
2
1
0
0
0
20
40
60
80
100
0
Dimming ratio (%)
0.2
0.4
0.6
0.8
1
Dimming ratio (%)
C015
Figure 11. PWM Dimming Linearity (0-100%) (fSW = 500kHz,
L1 = 68 µH
C016
Figure 12. PWM Dimming Linearity (under 1%) (fSW =
500kHz, L1 = 68 µH
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7 Detailed Description
7.1 Overview
The TPS92511 is an easy to use constant current buck converter for driving a single LED string with current up
to 0.5A and efficiency up to 95%. Only 5 external components are required for basic operation and single layer
PCB layout is feasible because of the integration of a N-MOSFET, no external current sensing resistor, no
external compensation and the proper pin assignment. A high-value external resistor programs the LED current
so that fine tuning of the LED current can be achieved. Another high-value external resistor programs a constant
switching frequency from 50kHz to 500kHz. As a result of constant switching frequency, EMI design becomes
easy. The TPS92511 provides a wide input voltage range from 4.5V to 65V. By adding simple external circuits,
it can handle applications with even higher input voltages.
The TPS92511 employs a proprietary Pulse-Level-Modulation (PLM) control scheme under continuous
conduction mode (CCM) to regulate the LED current without the need of sensing the LED current directly. It
applies a floating buck topology with a low-side N-channel power MOSFET, which does not need boot-strapping
capacitor, so that driving LED string under drop-out conditions and very high input voltages are feasible. For
multiple channel systems, the floating buck topology without external current sensing network together with the
proprietary control scheme allows a common-anode connection of the LED strings without external current
sensing network. This saves high-side current sensing wirings for separate driver boards and LED board
systems and significantly reduces the number of wiring, which can lower overall manufacturing cost.
The TPS92511 has very fast PWM dimming response time. There is almost no delay between the DIM pin
voltage rising edge and the start of the LED current conduction, so it can dim down to nearly zero current. In
order to maintain good dimming linearity, the minimum LED current pulse width is suggested to be three
switching cycles. For example, if the switching frequency is 500 kHz, the minimum DIM pulse width is 6µs and
the dimming frequency is 150Hz, a contrast ratio of more than 1000:1 can be achieved.
8
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7.2 Functional Block Diagram
VIN
FS
VCC
Voltage
Regulator
LX
Clock
Generator
Pulse Ref.
S
UVLO
+
-
VCC
+
-
VCC
Switch
Control logic
Q
R
3.75V
RISNS
VCC
6
DIM
1.0V
VCC
+
-
+
-
Slope Comp. Pulse Ref.
Current Mirror
PLM module
gm
+
1.25V
PGND
+
-
+
IADJ
GND
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7.3 Feature Description
7.3.1 Pulse Level Modulation (PLM) Control
A proprietary Pulse-Level-Modulation (PLM) control method is used in the TPS92511. It can regulate the
average LED current by sensing only the inductor current at the on-period (Figure 13). The integrated MOSFET
and the sensing and control circuits in the TPS92511 implement the whole PLM control internally so the control
does not suffer from tolerance and noise issues that may be coming from external components. As compared
with the conventional method which regulates average LED current by sensing the current over the entire
switching cycle, the power dissipation on the sensing circuit in PLM is much lower. For example, consider a duty
cycle of 0.5, the power dissipation on current sensing in PLM can be reduced by half. PLM requires no external
loop compensation circuit. Besides, the accuracy of the regulated LED current is high (typically ±3.5% in the
TPS92511).
ILX
IL1
Current
ILED(avg)
1/fSW .
tON
Time
Figure 13. Waveforms of a Floating Buck LED Driver with PLM
7.3.2 Pulse Level Modulation (PLM) Operaion Principles
The Pulse-Level-Modulation is a patented method to ensure an accurate average output current regulation
without the need of direct output current sensing. Figure 13 shows the current waveforms of a typical buck
converter under steady state, where, IL1 is the inductor current and ILX is the current flowing into the LX pin. For a
buck converter operating in steady state, the mid-point of the RAMP portion of IL1 equals to the average value of
IL1 and hence the average LED current ILED(avg). In short, by regulating the mid-point with respect to a precise
reference level, PLM achieves LED current regulation by sensing the main MOSFET current solely, instead of
the entire cycle of IL1.
7.3.3
PLM Control enable Common-Anode Low-Side Sensing (CALS)Technique to Save Wiring
For multi-channel systems with separated driver boards and LED array boards, the Pulse-Level-Modulation
(PLM) control scheme enable Common-Anode Low-Side Current Sensing to save inter-board wirings. Figure 14
shows a conventional configuration with a Low-side switching and High-Side Current Sensing. For an n channel
system with separated driver and an LED array boards, 2n inter-board wirings are required. For example, an
128-channel system needs 256 inter-board wirings, which implies a high material and manufacturing cost.
Figure 15 shows the PLM configuration with Low-side switching and Low-Side Current Sensing. A CommonAnode configuration is used for the LED array board. As shown in the figure, an n channel system with separated
driver and LED array boards requires only n+1 inter-board wirings. For an 128-channel system, only 129 interboard wirings are required. The wiring cost is cut by half, and the cost of the end product can be reduced.
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Feature Description (continued)
LED String
1
LED String
2
LED String
n
LED array board
Sensing
resistor 1
LED Driver 1
Sensing
resistor 2
LED driver board
Sensing
resistor n
LED Driver n
LED Driver 2
VIN
Figure 14. Conventional Configuration with Low-Side Switching and High-Side Current Sensing Requires
2×n Inter-Board Wirings
LED String
1
LED String
2
LED String
n
LED array board
LED driver board
LED Driver 1
LED Driver 2
LED Driver n
VIN
Figure 15. PLM Configuration with Common-Anode Low-Side Switching Requires n+1 Inter-Board
Wirings
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Feature Description (continued)
7.3.4 Internal Regulator
The TPS92511 integrates an internal voltage regulator for powering internal circuitry. For stability, an external
capacitor CVCC of at least 1 μF should be connected between the VCC and PGND pins The output of the internal
regulator VCC is 5.4V when VIN is larger than 6V. If VIN is lower than 6V, VCC decreases. The TPS92511 will
trigger the VCC under-voltage lock-out if VCC falls below typically 3.5V. VCC can be used to bias external circuits
subject to a loading of maximum 2 mA, while it has a short circuit current limit at typically 16 mA.
7.3.5 Setting The Switching Frequency
The switching frequency fSW of the TPS92511 is programmable in the range of 50 kHz to 500 kHz by a single
resistor RFS connecting the FS pin and ground. The following equation shows the relationship between fSW and
RFS:
fSW
10 u 10 6
kHz
RFS
(1)
Figure 16 plots fsw against RFS. Table 1 shows values of RFS for commonly used switching frequencies.
500
450
400
fSW (kHz)
350
300
250
200
150
100
50
20
40
60
80
100 120 140 160 180 200
RFS (k:)
C006
Figure 16. Switching Frequency vs RFS
Table 1. Commonly Used fSW And RFS
fSW (kHz)
RFS (kΩ)
50
200
100
100
300
33.2
500
20
7.3.6 Setting The LED Current
The LED current ILED of the TPS92511 is programmable by a single resistor RIADJ connecting the IADJ pin and
ground. The IADJ pin is internally biased to 1.25 V. Equation 2 shows the relationship between ILED and RIADJ:
1500
A
ILED
RIADJ
(2)
To ensure stability, RIADJ must be less that 30 kΩ, implying a minimum ILED of 50 mA can be programmed. The
tolerance of ILED of 150 mA is shown in the ELECTRICAL CHARACTERISTICS. Larger tolerance should be
expected for lower ILED. Figure 17 plots ILED against RIADJ. Table 2 shows values of RIADJ for commonly used ILED.
12
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0.5
0.45
0.4
ILED (A)
0.35
0.3
0.25
0.2
0.15
0.1
3
4
5
6
7
8
9
10
RIADJ (k:)
C007
Figure 17. LED Current vs
RIADJ
Table 2. Commonly Used ILED And RIADJ
ILED (mA)
RIADJ (kΩ)
150
10
350
4.32
500
3.01
7.3.7 Integrated MOSFET
The TPS92511 integrates a N-channel power MOSFET, the drain of which is connected to the LX pin. When the
integrated MOSFET is turned on, the resistance across the LX and GND pins is typically 1.4Ω. The integrated
MOSFET has a fixed current limit of 1.2A to protect the application circuit during critical operation conditions like
short circuit of the LED string. Once the limit is hit, the integrated MOSFET turns off immediately for 34 µs to let
the inductor discharge.
The minimum on-time of the integrated MOSFET is 400 ns. It may be hit at a high switching frequency and a
high VIN/VLED ratio. Once hit, the ILED regulation may be affected. In the worst case, ILED may be boost up to a
level higher than the programmed value, and the LED string and/or the inductor may be damaged as a result.
Hence, it is recommened that the ratio between VIN and VLED should be designed under the following constraint:
VLED
t 400ns u fSW
VIN
(3)
7.3.8 Inductor Selection
Operating in the continuous conduction mode (CCM) is required in the TPS92511 application circuit. In the CCM,
considering the on-period, the peak-to-peak inductor current ripple (2ΔIL1) is shown in Equation 4.
2'IL1
Because
VLED
VIN
t on VIN VLED
L1
(4)
t on fSW
(5)
L1 can be a function of VIN, VLED, fSW and ΔIL1 as shown in Equation 6 .
L1
VIN VLED VLED
2'IL1VIN fSW
(6)
The value of L1 is selected by designers with the consideration of all above parameters. The minimum L1
calculated by the following equation is a good starting point for designing L1:
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RFSRIADJ
10 6
(7)
The following table shows some typical examples of using RFS and RIADJ to estimate the minimum L1:
Table 3. Estimation Of Minimum L1 Using RFS And RIADJ
RFS (kΩ)
RIADJ (kΩ)
Estimated Minimum L1
(µH)
Recommended L1 (µH)
100
10
1000
1000
33.2
3.01
100
100
20
4.32
86
100
20
3.01
60
68
To maintain the CCM, ΔIL1 must be smaller than the average LED current ILED(avg). Hence, the minimum
inductance used is:
L1(min)
VIN VLED VLED
2ILED(avg ) VINfSW
(8)
In the absence of output capacitors, the TPS92511 can maintain a continuous ILED throughout the entire
switching cycle because in such case the inductor current is the same as ILED (floating buck topology operating in
the CCM). However, the LED peak current must not exceed the rated current of the LED. The peak LED current
can be found by the following equation:
ILED(peak )
7.3.9
ILED(avg)
VIN VLED VLED
2L1VINfSW
(9)
Integrated MOSFET Current Limit
The current limit of the integrated MOSFET is internally fixed at 1.2A to protect the LED string, the inductor and
the integrated MOSFET from overdriven. Once triggered, the integrated MOSFET turns off immediately for 34 µs
to let the inductor to discharge. The triggering of the current limit cycles repetitively until all overdriven conditions
disappear.
7.3.10 PWM Dimming Control
The TPS92511 implements PWM dimming by applying a PWM dimming signal to the DIM pin. A low input
applying to the DIM pin disables the switching of the integrated MOSFET, and as a result discharges the inductor
and then turns off the LED string. To turn on the LED string, the DIM pin should be connected to high or left open
(since it is internally pulled high by a current of typically 40 µA and 90 µA when the DIM pin is low and high
respectively). The PWM dimming frequency is recommended to be lower than 0.1fSW to ensure normal operation.
7.3.11
Analog Dimming
Analog dimming can be implemented by injecting a current to RIADJ (Figure 18) and as a result reduces the
current of the IADJ pin, IADJ, which is controlled internally by the TPS92511 to bias the voltage on the IADJ pin to
be 1.25V. If the CCM can be maintained, the minimum IADJ can achieve 15 µA, which refers to an ILED of 18
mA. If IADJ is further decreased, ILED may not follow due to the presence of the minimum on-time of the
integrated MOSFET. If the CCM cannot be maintained, ILED can still decrease monotonically with IADJ. However,
if good line and load regulations are required, the CCM should be maintained by using a large inductance.
14
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VIN
4.5V65VDC
TPS92511
VCC
CVCC
VIN
PGND
LX
LED string
D1
ILED
L1
CIN
IADJ
IADJ
RADIM
RIADJ
DIM
PWM dimming signal
GND
FS
RFS
VADIM
Figure 18. Circuit Configuration for Analog Dimming
7.3.12
High Voltage Buck Configuration
The TPS92511 can handle applications with an input voltage higher than 65V, which is the maximum VIN of the
recommended operating condition of the TPS92511, by adding an external high voltage N-channel MOSFET to
the application circuit as shown in Figure 19. PWM dimming can be implemented in this circuit without additional
efforts, and analog dimming is also feasible by referencing to additional circuits shown in Figure 18.
VSUPPLY
High
Voltage
DC
D1
High Voltage
Switching
Diode
VBIAS
8V-25VDC
LED string
L1
Q1
High Voltage
N-MOSFET
TPS92511
CIN
VCC
ILED
VIN
D2
CVCC
PGND
RIADJ
LX
IADJ
DIM
GND
FS
PWM dimming signal
RFS
Figure 19. Circuit Configuration for Very High Voltage Buck
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7.3.13 Thermal Foldback
Thermal foldback is useful to prevent over-temperature of LEDs during operation by sensing the temperature of
LEDs and, if the sensed temperature is high, reducing ILED to decrease the power and as well as the temperature
of LEDs. Thanks to the feature of analog dimming, thermal foldback can be implemented by embedding a
negative temperature coefficient (NTC) resistor, RNTC, into a circuit as shown in Figure 20. When the sensed
temperature increases, RNTC decreases and thus the emitter current of QT1 increases to reduce ILED by means of
analog dimming. The resistor RTF can adjust the loop gain of the thermal foldback control loop, which should be
high enough to avoid oscillation and maintain stability.
VIN
4.5V65VDC
TPS92511
VCC
CVCC
RNTC
VIN
PGND
LED string
D1
LX
ILED
L1
CIN
IADJ
QT1
RT1
IADJ
DIM
GND
FS
PWM dimming signal
RIADJ
RTF
RFS
Figure 20. Circuit Configuration for Thermal Foldback
7.3.14 EMI Consideration
Conductive and radiative EMI can be major concerns for lighting applications. The TPS92511 application circuit
can be designed for the EN 55022 class B standard by adding a few external components, as shown in
Figure 21. The input filter which consists of an inductor L2 and two capacitors CIN2 and CIN3 takes care of the
conductive EMI, while the output capacitor CLED and the ferrite bead FB1 which inserts between the LX pin and
D1 take care of the radiative EMI.
L2
Input EMI filter
VIN
48V
D1
100V
2A
TPS92511
VCC
CLED
1 PF
50V
VIN
FB1
100:@
100 MHz
38V LED string
10 PH
ILED
CIN
2.2 PF
100V
CIN3
CIN2
2.2 PF
100V
2.2 PF
100V
L1
PGND
LX
IADJ
DIM
GND
FS
100 PH
PWM
dimming
signal
CVCC
1PF
16V
RIADJ
3.01 k:
RFS
33.2 k:
Figure 21. Circuit Configuration with EMI Design Consideration
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7.4 Device Functional Modes
7.4.1 Operation with VIN < 4.5 V (minimum VIN)
For the typical application circuit, when the input voltage drops so that the VCC voltage regulator is under dropout mode, and the VCC voltage drops below the “VCC UVLO Lower Threshold” (typically 3.48V), the switching of
the main MOSFET is stopped, and the LED current will become zero. At the same time, the voltages of both the
FS and IADJ pins will become zero .
When the input voltage increases from zero and the VCC voltage is increased to cross over the “VCC UVLO
Upper Threshold” (typically 3.75V), the voltages on the FS and IADJ pins will rise to their regulation voltage
(typically 1.25V), the switching of the main MOSFET is started upon the DIM pin voltage is HIGH, and the LED
current will ramp up to its preset value set by RIADJ.
7.4.2 Operation with DIM control
For the typical application circuit, when the VCC voltage is not under UVLO condition, the switching of the main
MOSFET is enabled and the LED current is conducted if the DIM pin voltage is higher than the “DIM Pin Upper
Threshold” (typically 1V).
Alternaltively, the switching is disabled and the LED current is cut off if the voltage of the DIM pin is lower than
the “DIM Pin Lower Threshold” (typically 0.675V).
7.4.3 Linear Mode
When the VCC voltage is not under UVLO condition and the voltage on the FS pin is forced to be higher than
4.2V but lower than 5V, the switching of the main MOSFET is disabled, and the TPS92511 is working in the
Linear Mode. In the Linear Mode, if the voltage on the DIM pin is higher than the “DIM Pin Upper Threshold”
(typically 1V), the TPS92511 will regulate the LX pin in-going current according to the preset value set by RIADJ.
Alternatively, if the voltage on the DIM pin is lower than the “DIM Pin Lower Threshold” (typically 0.675V), the LX
pin will open and its in-going current will become zero.
Below is the simple configuration to have the TPS92511 working as a linear current shunt regulator.
VIN
4.5V65VDC
TPS92511
VCC
LED string
VCC
ILED
VIN
CIN
CVCC
PGND
IADJ
RIADJ
LX
DIM
PWM dimming signal
1 k:
GND
VCC
FS
5V
sharp
knee
point
Figure 22. Circuit Configuration for Working as a Linear Current Shunt Regulator
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8 Application and Implementation
8.1 Application Information
The TPS92511 is an LED driver which provides a regulated output current to drive a single string of LED with the
forward voltage lower than the input voltage. The following procedures design a TPS92511 application circuit
with an input voltage of 48V, driving an LED string of 38V at an LED current of 0.5A. The switching frequency is
300 kHz.
8.2 Typical Application
8.2.1
TPS92511 LED driver for 12 LEDs at 0.5A
VIN
D1
100V
2A
TPS92511
VCC
38V LED string
48V
ILED
CIN
2.2 PF
100V
VIN
L1
PGND
CVCC
1PF
16V
RIADJ
LX
IADJ
DIM
GND
FS
100 PH
PWM
dimming
signal
3.01 k:
RFS
33.2 k:
Figure 23. Application Circuit of TPS92511 (fSW = 300 kHz and ILED = 0.5A)
18
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Typical Application (continued)
8.2.1.1 Design Requirements
Table 4. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
43V to 53V
LED current
0.5A
LED string forward voltage
38V
Operating frequency
300 kHz
8.2.1.2 Detailed Design Procedure
CIN : The function of the input capacitor CIN is to reduce the input voltage ripple. Ceramic capacitors are
recommended owing to the concern of product lifetime. A 100V 2.2 µF ceramic capacitor is selected in this
circuit.
CVCC : The capacitor on the VCC pin provides noise filtering and stabilizes the internal regulator. It also prevents
false triggering of the VCC UVLO. CVCC is recommended to be a 1 μF good quality and low ESR ceramic
capacitor.
D1 : The diode D1 should have a reverse voltage larger than VIN in the floating buck topology. In this circuit, a
100V diode is selected.
RFS and RIADJ : In this circuit, the switching frequency and LED current are designed to be 300 kHz and 0.5A.
From Table 1 and Table 2, RFS is 33.2 kΩ and RIADJ is 3.01 kΩ.
L1 : The selection of inductor mainly affects the inductor current ripple. In this circuit, we design the peak to peak
inductor current ripple to be 50% of ILED, i.e. 0.25A. From (6), L1 is calculated to be 106 µH, and a 100 µH
inductor is selected.
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8.2.1.3 Application Curves
5
100
4
3
'ILED Regulation (%)
Efficiency (%)
90
80
70
1 LEDs
3 LEDs
60
7 LEDs
50
0
10
20
30
40
1
0
-2
-3
12 LEDs
-4
50
60
1 LEDs
3 LEDs
7 LEDs
10 LEDs
12 LEDs
19 LEDs
-1
10 LEDs
19 LEDs
40
2
-5
0
70
10
VIN (V)
20
30
40
50
60
70
VIN (V)
C004
Figure 24. Efficiency vs VIN
C005
Figure 25. LED Current Regulation vs VIN
VIN
VLX
VLX
ILED
ILED
Figure 26. Steady State Operation
VDIM
VDIM
VLX
VLX
ILED
ILED
Figure 28. PWM Dimming (VDIM Rising)
20
Figure 27. Power Up
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Figure 29. PWM Dimming (VDIM Falling)
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VDIM
VDIM
VLX
VLX
ILED
ILED
Figure 30. PWM Dimming (fDIM = 1 kHz, 50% Duty Cycle)
Figure 31. PWM Dimming (9 µs dimming pulse) (fSW =
500kHz, L1 = 68 µH)
9 Power Supply Recommendation
This device is designed to operate from an input voltage supply range between 4.5 V and 65 V. The input supply
should be well regulated. If the input supply is located more than a few inches from the TPS92511 application
board, additional bulk capacitance may be required in addition to the input capacitor. A ceramic capacitor with a
value of 2.2 μF is a typical choice.
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10 Layout
10.1 Layout Guidelines
•
•
•
•
•
The PCB layout of the TPS92511 application circuit plays an important role in optimizing the performance.
The external components should be placed as close to the TPS92511 as possible to minimize resistance and
parasitic inductance of copper traces.
For example, D1 and L1 should be near the LX pin, and CVCC should be near the VCC pin, and the connecting
copper traces are short and thick.
The exposed pad of the TPS92511, which is internally connected to the die substrate, should be connect to a
ground plane, and the plane should be extended as much as possible on the same copper layer around the
TPS92511.
Using numerous vias beneath the exposed pad to dissipate heat to another copper layer is also a good
practice.
10.2 Layout Example
LED-
VIN, LED+
GND
CIN
D1
L1
CVCC
DIM
RIADJ
RFS
Figure 32. TPS92511 Board Layout
10.2.1 Thermal Consideration
ΨJT (shown in session 6.4 Thermal Information) is a relatively small value for package with exposed pad since
most of the heat is dissipated through the exposed pad to the copper plate of the PCB (assuming optimized PCB
layout), relatively little heat goes to the top of the device. The top of the device mold compound temperature is
physically close to the device junction temperature.
For example, a 30W output TPS92511 end system at 95% power efficiency (can be estimated from the efficiency
curves of Figure 13), power loss is 1.6W. Assuming all the heat is generated from the TPS92511 (which is true
for high VLED), and assuming half of the heat generated is dissipated through the top of the device. Now ΨJT is
11 °C/W, the device junction temperature is estimated to be higher than the package’s top-surface temperature
by 11 x 1.6 x 0.5 = 8.8 (°C). If the package top-surface temperature is measured to be 90 °C (for example by an
IR camera), the device junction temperature is around 99 °C, which is within the 125°C maximum junction
temperature requirement with margin.
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11 Device and Documentation Support
11.1 Trademarks
All trademarks are the property of their respective owners.
11.2 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.3 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical packaging and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
TPS92511DDA
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
92511
TPS92511DDAR
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
92511
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
