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ZXLD1374
60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER
Description
The ZXLD1374 is an LED driver converter IC with integrated 1.5A low side switch to drive high current LEDs. It is a multitopology converter enabling it to efficiently control the current through series connected LEDs. The multi-topology enables it to operate in Buck, Boost and Buck-boost configurations. The 60V capability coupled with its multi-topology capability enables it to be used in a wide range of applications and drive in excess of 16 LEDs in series. The ZXLD1374 is a modified hysteretic converter using a patent pending control scheme providing high output current accuracy in all three topologies. High accuracy dimming is achieved through DC control and high frequency PWM control. The ZXLD1374 uses two pins for fault diagnosis. A flag output highlights a fault, while the multi-level status pin gives further information on the exact fault.
Pin Assignments
TSSOP-20EP
ADJ REF TADJ SHP STATUS SGND PGND PGND N/C N/C 1 2 3 4 5 6 7 8 9 10 ZXLD1374 Thermal Pad 20 19 18 17 16 15 14 13 12 11 GI PWM FLAG ISM VIN VAUX LX LX N/C N/C
NEW PRODUCT
Features
* * * * * 0.5% typical output current accuracy 6.3 to 60V operating voltage range 1.5A integrated low side switch LED driver supports Buck, Boost and Buck-boost topologies Wide dynamic range dimming o 20:1 DC dimming o 1000:1 dimming range at 500Hz * * * Up to 1MHz switching High temperature control of LED current using TADJ Green mold compound (No Br, Sb) and RoHS compatible
Typical Application Circuit
Curve showing LED current vs. TLED
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Pin Descriptions
Pin Name Pin Type (Note 1) Description Adjust input (for dc output current control) Connect to REF to set 100% output current. Drive with dc voltage (125mVADJ
1
I
REF
2
O
NEW PRODUCT
TADJ
3
I
SHP
4
I/O
STATUS
5
O
SGND PGND N/C LX VAUX
6 7,8 9, 10, 11, 12 13, 14 15
P P O P
VIN ISM
16 17
P I
FLAG
18
O
PWM
19
I
GI
20
I
EP
Notes:
PAD
P
1. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)
Symbol VIN VAUX VISM VSENSE VLX ILX ISTATUS VFLAG VPWM, VADJ, VTADJ, VGI TJ TST Parameter Input supply voltage relative to GND Auxiliary supply voltage relative to GND Current monitor input relative to GND Current monitor sense voltage (VIN-VISM) Low side switch output voltage to GND Low side switch continuous output current Status pin output current Flag output voltage to GND Other input pins to GND Maximum junction temperature Storage temperature Rating -0.3 to 65 -0.3 to 65 -0.3 to 65 -0.3 to 5 -0.3 to 65 1.8 1 -0.3 to 40 -0.3 to 5.5 150 -55 to 150 Unit V V V V V A mA V V C C
NEW PRODUCT
These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices. Notes: For correct operation SGND and PGND should always be connected together.
Package Thermal Data
Thermal Resistance Junction-to-Case, JC Package TSSOP-20EP 4 Unit C/W
Recommended Operating Conditions
Symbol VIN VAUX VSENSE VLX ILX VADJ ISTATUS IREF fSW VTADJ fPWM tPWMH/L VPWMH VPWML TJ GI
Notes:
Parameter Input supply voltage range Auxiliary supply voltage range (Note 3)
Differential input voltage Low side switch output voltage Low side switch continuous output current External dc control voltage applied to ADJ DC brightness control mode pin to adjust output current from 10% to 200% Status pin output current Reference external load current REF sourcing current Recommended switching frequency range (Note 4) Temperature adjustment (TADJ) input voltage range To maintain 1000:1 resolution Recommended PWM dimming frequency range To maintain 200:1 resolution PWM pulse width in dimming mode PWM input high or low PWM pin high level input voltage PWM pin low level input voltage Operating Junction Temperature Range Gain setting ratio for Boost and Buck-boost modes Ratio= VGI/VADJ
Performance/Comment Normal operation Functional (Note 2) Normal operation Functional VVIN-VISM, with 0 VADJ 2.5
Min 8 6.3 8 6.3 0
Max 60 60 450 60 1.5 2.5 100 1 1000 VREF 500 1000 10 5.5 0.4 125 0.50
Unit V V mV V A V A mA kHz V Hz Hz ms V V C
0.125
300 0 100 100 0.005 2 0 -40 0.20
2. The functional range of VIN is the voltage range over which the device will function. Output current and device parameters may deviate from their normal values for VIN and VAUX voltages between 6.3V and 8V, depending upon load and conditions. 3. VAUX can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a voltage should not be applied to VAUX in the absence of a voltage at VIN. 4. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency is not tested in production.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Electrical Characteristics
(Test conditions: VIN = VAUX = 12V, TA = 25C, unless otherwise specified.)
NEW PRODUCT
Symbol Parameter Supply and reference parameters Under-Voltage detection threshold VUVNormal operation to switch disabled Under-Voltage detection threshold VUV+ Switch disabled to normal operation IQ-IN Quiescent current into VIN IQ-AUX Quiescent current into VAUX ISB-IN Standby current into VIN. ISB-AUX Standby current into VAUX. VREF Internal reference voltage Change in reference voltage with output VREF current VREF_LINE Reference voltage line regulation VREF-TC Reference temperature coefficient DC-DC converter parameters VADJ
Conditions VIN or VAUX falling VIN or VAUX rising PWM pin floating. Output not switching PWM pin grounded for more than 15ms No load Sourcing 1mA Sinking 25A VIN = VAUX , 6.5VMin
Typ
Max
Units V V mA A A A V mV dB ppm/C
5.2 5.5
5.6 6 1.5 150 90 0.7 1.25
6.3 6.5 3 300 150 10 1.263 5
1.237 -5 -60
-90 +/-50
External dc control voltage applied to ADJ DC brightness control mode 0.125 pin to adjust output current (Note 5) 10% to 200% VADJ 2.5V IADJ ADJ input current (Note 5) VADJ = 5.0V GI Voltage threshold for Boost and BuckVGI VADJ = 1.25V boost modes selection (Note 5) VGI 2.5V IGI GI input current (Note 5) VGI = 5.0V IPWM PWM input current VPWM = 5.5V PWM pulse width tPWMoff PWM input low 10 (to enter shutdown state) Thermal shutdown upper threshold TSDH Temperature rising. (LX output inhibited) Thermal shutdown lower threshold TSDL Temperature falling. (LX output re-enabled) High-Side Current Monitor (Pin ISM) IISM Input Current Measured into ISM pin and VISM = VIN Accuracy of nominal VSENSE threshold VSENSE_acc voltage VADJ = 1.25V VSENSE-OC Over-current sense threshold voltage 300
Notes:
1.25
2.5 100 5 0.8 100 5 100 25
V nA A V nA A A ms C C
36 15 150 125
11 0.25 350
20 2 375
A % mV
5. The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This limits the switch current should those pins get overdriven.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Electrical Characteristics
(Test conditions: VIN = VAUX = 12V, TA = 25C, unless otherwise specified.)
Symbol Parameter Output Parameters VFLAGL FLAG pin low level output voltage IFLAGOFF FLAG pin open-drain leakage current
Conditions Output sinking 1mA VFLAG=40V Normal operation Out of regulation (VSHP out of range) (Note 7) VIN under-voltage (VIN < 5.6V) Switch stalled (tON or tOFF> 100s) LX over-voltage state (VLX >60V) Over-temperature (TJ > 125C) Excess sense resistor current (VSENSE > 0.375V) Excessive switch current (ISW>1.5A) Normal operation Output stage off, VLX = 60V (Note 8) ILX = 1.5A (tON < 100s)
Min
Typ
Max 0.5 1 4.8 3.9 3.9 3.9 3.0 2.1 1.2 1.2
Units V A
4.2 3.3 3.3 3.3 2.4 1.5 0.6 0.6
4.5 3.6 3.6 3.6 2.7 1.8 0.9 0.9 10 60 0.5 86
NEW PRODUCT
VSTATUS
STATUS Flag no-load output voltage (Note 6)
V
RSTATUS Output impedance of STATUS output Low side switch output (LX pins tied together) ILX-LG RDS(ON) tPDHL tPDLH tLXR tLXF tSTALL Low side switch leakage current LX pin MOSFET on resistance Propagation delay high-low Propagation delay low-high LX output rise time LX output fall time
k A 0.8 ns ns ns ns 170 s
VSENSE = 225mV 30%, CL = 680pF, RL = 120
131 208 12 100
Time to assert `STALL' flag and warning on STATUS output LX low or high (Note 9) LED Thermal control circuit (TADJ) parameters Onset of output current reduction VTADJH Upper threshold voltage (VTADJ falling) Output current reduced to <10% of VTADJL Lower threshold voltage set value (VTADJ falling) ITADJ TADJ pin Input current VTADJ = 1.25V
Notes:
560 380
625 440
690 500 1
mV mV A
6. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g. `Excessive coil current' and `Out of regulation' occurring together will produce an output of 0.9V on the STATUS pin. The voltage levels on the STATUS output assume the Internal regulator to be in regulation and VADJ<=VREF. A reduction of the voltage on the STATUS pin will occur when the voltage on VIN is near the minimum value of 6V. 7. Flag is asserted if VSHP<2.5V or VSHP>3.5V 8. With the device still in switching mode the LX pin has an over-voltage detection circuit connected to it with a resistance of approximately 1M. 9. If tON exceeds tSTALL, LX turns off and then an initiate a restart cycle occurs. During this phase, ADJ is grounded internally and the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be repeated automatically until the operating conditions are such that normal operation can be sustained. If tOFF exceeds tSTALL, the switch will remain off until normal operation is possible.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Typical Characteristics
3
1500 900
2.5
Supply Current (mA)
1250
750
Switching Frequency (kHz)
Switching Frequency (kHz)
LED Current (mA)
2
1000
ILED
600
1.5
750
Switching Frequency
450
NEW PRODUCT
1
500
TA = 25C V AUX = VIN = 12V 2LEDs L = 33 H RS = 300m
300
0.5
250
150
0
6
24 30 36 42 48 54 60 Supply Voltage (V) Figure 1. Supply Current vs. Supply Voltage
1400 1200
Switching Frequency (kHz)
12
18
0 1.5 2.5 1 2 ADJ Voltage (V) Figure 2. Buck LED Current, Switching Frequency vs. V ADJ 0 0.5
700 650 600 550
LED Current (mA)
0
700 650 600 550 500
LED Current (mA)
700 600 500
ILED
1000
ILED
500 450 400 350 300 250 200 150 100 50 0 0
TA = 25C V AUX = VIN = 12V 12 LEDs L = 33 H R S = 300m Switching Frequency
450 400 350 300 250 200 150 100 50 0 0 0.5
TA = 25 C V AUX = VIN = 24V 8LEDs L = 33 H GI = 0.23 RS = 300m Switching Frequenc y
800 600 400 200
400 300 200 100
0 1 1.5 2 2.5 ADJ Voltage Figure 3. Buck-Boost LED Current, Switching Frequency vs. V ADJ
1500
V IN = 24V TA = 25 C IPWM = 100Hz ILED
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 ADJ Voltage Figure 4. Boost LED Current, Switching Frequency vs. V ADJ
1250
LED Current (mA)
1000
750
500
250
0
0
10
20
30 40 50 60 70 80 90 100 PWM Duty Cycle (%) Figure 5. ILED vs. PWM Duty Cycle
Figure 6. ILED vs time - PWM pin transient response
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ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Typical Characteristics
100%
1.252 1.2515
LED Current Dimming Factor
80%
1.251
Reference Voltage (V)
60%
1.2505 1.25 1.2495 1.249
NEW PRODUCT
40%
20%
1.2485
0%
0
500 750 1000 TADJ Pin Voltage (mV) Figure 7. LED Current vs. TADJ Voltage
250
1250
1.248 -40 -25 -10
5 20 35 50 65 80 95 110 125 Junction Temperature (C) Figure 8. VREF vs. Temperature
TA = 25 C L = 33H RS = 150m Buc k Mode 2 LED S
0.9 0.8
Power Switch On-Resistance ()
100% 90% 80% 70% 60%
0.7 0.6
Duty
V IN = 12V ILX = 1.3A
0.5 0.4 0.3 0.2 0.1 0 -40 -25 -10
50% 40% 30% 20% 10% 0% 6 12 24 30 36 42 48 54 Input Voltage (V) Figure 10. Duty Cycle vs. Input Voltage 18 60
5 20 35 50 65 80 95 110 125 Junction Temperature (C) Figure 9. RDS(ON) vs. Temperature
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Typical Characteristics - Buck Mode - RS = 146m - L = 33H - ILED = 1.5A
1.65
TA = 25C V AUX = VIN L = 33H RS = 146m 9 LED s 11 LED s 13 LEDs 15 LEDs
1.60
LED Current (A)
1.55
1.50
NEW PRODUCT
1.45
1 LED
3 LED s
5 LED s
7 LED s
1.40
1.35
6
12
30 36 48 42 Input Voltage (V) Figure 11. Load Current vs. Input Voltage and Number of LED 24
18
54
60
1200
TA = 25C V AUX = VIN L = 33H R S = 146m
1000
Switching Frequency (kHz)
800
600
400
200
3 LED s 7 LED s 5 LED s 9 LED s 11 LED s 13 LEDs 15 LEDs 1 LED
0
6
12
30 36 42 48 Input Voltage (V) Figure 12. Frequency vs. Input Voltage and Number of LED
18
24
54
60
100% 95%
5 LEDs
15 LEDs
90% 85% 80%
1 LED 3 LEDs 7 LEDs 9 LEDs 11 LED s 13 LEDs
Efficiency
75% 70% 65% 60% 6 12 18 30 36 42 48 Input Voltage (V) Figure 13. Efficiency vs. Input Voltage and Number of LED 24
TA = 25C V AUX = VIN L = 33H RS = 146m
54
60
ZXLD1374
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ZXLD1374 Typical Characteristics - Buck Mode - RS = 291m - L = 33H - ILED = 750mA
0.825
TA = 25C V AUX = VIN L = 33H RS = 291m 3 LEDs
0.800
7 LEDs 5 LEDs 9 LEDs
11 LED s 13 LEDs
15 LEDs
LED Current (A)
0.775
1 LED
0.750
NEW PRODUCT
0.725
0.700
0.675
6
12
18
30 36 48 42 Input Voltage (V) Figure 14. ILED vs. Input Voltage and Number of LED 24
11 LED s 9 LED s
54
60
1000 900 800 Frequency (kHz) 700 600 500 400 300 200 100 0 6
TA = 25C V AUX = VIN L = 33H RS = 291m 7 LED s
5 LED s
3 LED s
13 LEDs
15 LEDs
1 LED
12
18
30 36 42 48 Input Voltage (V) Figure 15. Frequency ZXLD1374 - Buck Mode = L = 47 H
7 LED s 9 LED s 11 LED s 13 LEDs
24
54
60
100% 95%
5 LED s
15 LEDs
3 LED s
90% 85%
Efficiency
80% 75% 70%
TA = 25C
1 LED
65% 60% 6
V AUX = VIN L = 33H R S = 291m
12
18
30 36 42 48 Input Voltage (V) Figure 16. Efficiency vs. Input Voltage and Number of LED
24
54
60
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Typical Characteristics - Boost mode - RS = 150m - L = 33H - ILED = 325mA - GIRATIO = 0.21
0.358
TA = 25 C L = 33H R S = 150m R GI1 = 33k R GI2 = 120k
0.347
LED Current (A)
0.336
0.325
NEW PRODUCT
0.314
6 LED s
0.303
8 LED s
10 LEDs
12 LEDs
14 LEDs
16 LEDs
0.292 12
17
22
27 32 37 Input Voltage (V) Figure 17. ILED vs. Input and Number of LED
42
47
700 650 600
TA = 25 C L = 33H R S = 150m R GI1 = 33k R GI2 = 120k
Frequency (kHz)
550 500 450 400 350 300
6 LED s 12 LEDs 14 LEDs 16 LEDs
250 200 12 17
8 LED s
10 LEDs
32 37 27 Input Voltage (V) Figure 18. Frequency vs. Input Voltage and Number LED 22
8 LED s 10 LEDs 12 LEDs 14 LEDs
42
47
100%
6 LED s 16 LEDs
95%
Efficiency
90%
85%
TA = 25 C
80%
L = 33H R S = 150m R GI1 = 33k R GI2 = 120k
75% 12
17
32 37 27 Input Voltage (V) Figure 19. Efficiency vs. Input Voltage and Number of LED 22
42
47
ZXLD1374
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ZXLD1374 Typical Characteristics - Boost mode - RS = 150m - L = 33H - ILED = 350mA - GIRATIO = 0.23 - with bootstrap
0.385
0.368
LED Current (A)
11 LE Ds
13 LEDs
15 LEDs
0.350
7 LEDs 9 LEDs 5 LEDs T A = 2 5 C L = 3 3H R S = 1 50m R GI1 = 36m R GI2 = 120m
NEW PRODUCT
0.333
0.315 6.5
8
11 12.5 14 15.5 Input Voltage (V) Figure 20. Load Current vs. Input Voltage and Number of LED
9.5
17
700 600
Switching Frequency (kHz)
15 LEDs
500
11 LED s
13 LEDs
400
9 LEDs 7 LEDs
300
5 LEDs
200
TA = 25 C L = 33H RS = 150m RGI1 = 36m RGI2 = 120 m
100 0 6.5
100%
8
12.5 11 14 Input Voltage (V) Figure 21. Frequency vs. Input Voltage and N umber of LED
9.5
15.5
17
7 LED s 5 LED s
95%
90%
15 LEDs
Efficiency
85%
13 LEDs
80%
9 LED s 11 LED s TA = 25 C L = 33H RS = 150m
75%
70% 6.5
8
12.5 11 14 Input Voltage (V) Figure 22. Efficiency vs. Input Voltage and Number of LED
9.5
15.5
17
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Typical Characteristics - Buck-boost mode - RS = 150m - L = 33H - ILED = 350mA - GIRATIO = 0.23 - with bootstrap
0.385 0.375 0.365
LED Current (mA)
6 LED s
7 LED s
8 LED s
0.355 0.345
3 LED s 4 LED s 5 LED s TA = 25 C L = 33H RS = 150m RGI1 = 36 m RGI2 = 120m
NEW PRODUCT
0.335 0.325 0.315 6.5
8.0
11.0 12.5 14.0 Input Voltage (V) Figure 23. LED Current vs. Input Voltage and Number of LED
6 LED s 7 LED s
9.5
15.5
17.0
600
8 LED s
500
Switching Frequency (kHz)
400
300
5 LED s
4 LED s
3 LED s
200
TA = 25 C L = 33H RS = 150m RGI1 = 36k RGI2 = 120k
100
0 6.5 8.0 9.5
14.0 15.5 11.0 12.5 Input Voltage (V) Figure 24. Switching Frequency vs. Input Voltage and Number of LED
17.0
100%
TA = 25 C L = 33H RS = 150m RGI1 = 36K RGI2 = 120k
95%
90%
Efficiency
85%
80%
75%
8 LED s
7 LED s
6 LED s
5 LED s
4 LED s
3 LED s
70% 6.5
8.0
11.0 12.5 14.0 Input Voltage (V) Figure 25. Efficiency vs. Input Voltage and Number of LED
9.5
15.5
17.0
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information
The ZXLD1374 is a high accuracy hysteretic inductive Buck/Boost/Buck-boost converter with an internal NMOS switch designed to be used for current-driving single or multiple series-connected LEDs. The device can be configured to operate in Buck, Boost, or Buck-boost modes by suitable configuration of the external components as shown in the schematics shown in the device operation description.
Device Operation
a) Buck mode
The most simple Buck circuit is shown in Figure 26 LED current control in Buck mode is achieved by sensing the coil current in the sense resistor Rs, connected between the two inputs of a current monitor within the control loop block. An output from the control loop drives the input of a comparator which drives the gate of the internal NMOS switch transistor. When the switch is on, current flows from VIN, via Rs, LED, coil and switch to ground. This current ramps up until an upper threshold value is reached. At this point the switch is turned off and the current flows via Rs, LED, coil and D1 back to VIN. When the coil current has ramped down to a lower threshold value the switch is turned on again and the cycle of events repeats, resulting in continuous oscillation.
NEW PRODUCT
VIN Rs LED1 D1 VAUX VIN PWM GI ADJ C2 REF TADJ SHP STATUS SGND LX LX FLAG NC x4 PGND L1 ISM LEDn
C1 GND
The average current in the LED and coil is equal to the average of the maximum and minimum threshold currents. The ripple current (hysteresis) is equal to the difference between the thresholds. The control loop maintains the average LED current at the set level by adjusting the thresholds continuously to force the average current in the coil to the value demanded by the voltage on the ADJ pin. This minimizes variation in output current with changes in operating conditions. The control loop also attempts to minimize changes in switching frequency by varying the level of hysteresis. The hysteresis has a defined minimum (typ 5%) and a maximum (typ 20%), the frequency may deviate from nominal in extreme conditions. Loop compensation is achieved by a single external capacitor C1, connected between SHP and SGND.
Figure 26. Buck Configuration
Figure 27. Operating Waveforms (Buck Mode)
ZXLD1374
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ZXLD1374 Applications Information (Continued)
b) Boost and Buck-boost modes A basic ZXLD1374 application circuit for Buck-boost and Boost modes is shown in Figure 28.
Control in Boost and Buck-boost mode is achieved by sensing the coil current in the series resistor Rs, connected between the two inputs of a current monitor within the control loop block. An output from the control loop drives the input of a comparator which drives the gate of the internal NMOS switch transistor. In Boost and Buck-boost modes, when the switch is on, current flows from VIN, via Rs, coil and switch to ground. This current ramps up until an upper threshold value is reached. At this point the switch is turned off and the current flows via Rs, coil, D1 and LED back to VIN (Buck-boost mode), or GND (Boost mode). When the coil current has ramped down to a lower threshold value the switch is turned on again and the cycle of events repeats, resulting in continuous oscillation. The average current in the coil is equal to the average of the maximum and minimum threshold currents and the ripple current (hysteresis) is equal to the difference between the thresholds. The average current in the LED is always less than the average current in the coil and the ratio between these currents is set by the values of external resistors RGI1 and RGI2. The peak LED current is equal to the peak coil current. The control loop maintains the average LED current at the set level by adjusting the thresholds and the hysteresis continuously to force the average current in the coil to the value demanded by the voltage on the ADJ and GI pins. This minimizes variation in output current with changes in operating conditions. Loop compensation is achieved by a single external capacitor C2, connected between SHP and SGND. For more detailed descriptions of device operation and for choosing external components, please refer to the application circuits and descriptions in the later sections of this specification.
NEW PRODUCT
Figure 28. Boost and Buck-boost Configuration
Figure 29. Operating Waveforms (Boost and Buck-boost Modes)
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information (Continued)
Component Selection
External component selection is driven by the characteristics of the load and the input supply, since this will determine the kind of topology being used for the system. Component selection starts with the current setting procedure and the inductor/frequency setting. Finally after selecting the freewheeling diode and the output capacitor (if needed), the application section will cover the PWM dimming and thermal feedback.
Setting the output current
NEW PRODUCT
The first choice when defining the output current is whether the device is operating with the load in series with the sense resistor (Buck mode) or whether the load is not in series with the sense resistor (Boost and Buck-boost modes). The output current setting depends on the choice of the sense resistor RS, the voltage on the ADJ pin and the voltage on the GI pin, according to the device working mode. The sense resistor RS sets the coil current IRS. The ADJ pin may be connected directly to the internal 1.25V reference (VREF) to define the nominal 100% LED current. The ADJ pin can also be overdriven with an external dc voltage between 125mV and 2.5V to adjust the LED current proportionally between 10% and 200% of the nominal value. ADJ and GI are high impedance inputs within their normal operating voltage ranges. An internal 2.6V clamp protects the device against excessive input voltage and limits the maximum output current to approximately 4% above the maximum current set by VADJ if the maximum input voltage is exceeded. Below are provided the details of the LED current calculation both when the load in series with the sense resistor (Buck mode) and when the load is not in series with the sense resistor (Boost and Buck-boost modes). In Buck mode, GI is connected to ADJ which results in the average LED current (ILED) equal to the average sense resistor/coil current (IRS). A loop gain compensation factor, K, compensates for GI being connected to ADJ. This gives the following equation for ILED:
RS
VIN
ISM
REF
ILED
=
IRs
225mV VADJ 218mV VADJ where K = 0.97 =K = RS VREF RS VREF
ADJ
If ADJ (and GI pin) is directly connected to VREF, this becomes: ILED Therefore: 218mV Rs = ILED = IRs = 218mV RS
GI
SGND
Figure 30: Buck configuration
In Boost and Buck-boost mode GI is connected to ADJ through a voltage divider. With VADJ equal to VREF, the ratio defined by the resistor divider at the GI pin determines the ratio of average LED current (ILED) to average sense resistor/coil current.
RS
VIN
ISM
ICOIL
Where
=
ILED 1- D
VRS = ICOIL xRS =
ILED xRS 1- D
R GI2
REF
ADJ
ILED
=
VGI VADJ 0.225 = VADJ VREF R S
R GI1
GI
=
Therefore:
R GI1 VADJ 0.225 (R GI1 + R GI2 ) VREF R S Rs = RGI1 225mV VADJ (RGI1 + RGI2 ) ILED VREF
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SGND
Figure 31: Boost and Buck-boost connection
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ZXLD1374 Applications Information (Continued)
When the ADJ pin is directly connected to the REF pin, this becomes:
Rs =
RGI1 225mV (RGI1 + RGI2 ) ILED
Note that the average LED current for a Boost or Buck-boost converter is always less than the average sense resistor current. For the ZXLD1374, the recommended potential divider ratio is given by:
0. 2
NEW PRODUCT
RGI1 0.50 (RGI1 + RGI2 )
It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current. In general the design procedure to follow is: Define input conditions in terms of VIN and IIN Set output conditions in terms of LED current and the number of LEDs Define controller topology - Buck, Boost or Buck-boost
Calculate the maximum duty-cycle as:
Buck mode
D MAX =
VLEDs VINMIN
Boost mode
DMAX =
Buck-boost mode
VLEDS - VIN MIN VLEDS
DMAX =
VLEDS VLEDS + VIN MIN
Set the appropriate GIRATIO according to the circuit duty and the max switch current admissible limitations
GIRATIO =
Set RGI1 as:
VGI RGI1 = 1 - DMAX VADJ (RGI1 + RGI2 )
10k R GI1 200k
Calculate RGI2 as:
R GI2
Calculate the sense resistor as:
D MAX x R GI1 1 - D MAX
Rs =
R GI1 225mV (R GI1 + R GI2 ) ILED
If the potential divider ratio is greater than 0.64, the device detects that Buck-mode operation is desired and the output current will deviate from the desired value.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information (Continued)
For example, as in the typical application circuit, in order to get ILED= 350mA with IRS=1.5A the ratio has to be set as:
ILED VGI RGI1 = = 0.23 IRS VADJ (RGI1 + RGI2)
Setting RGI1= 33k it results
R GI2 = R GI1(
VADJ - 1) =110k VGI
NEW PRODUCT
This will result in: Rs = R GI1 225mV = 150m (R GI1 + R GI2 ) ILED
Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors:
Table 1
GIRATIO RGI1 RGI2 0.2 30k 120k 0.25 33k 100k 0.3 39k 91k 0.35 30k 56k 100k 150k 0.4 51k 62k 0.45 0.5 30k 30k The values shown have been chosen so that they do not load REF too much or create offset errors due to the GI pin input current. A ZXLD1374 calculator is available from http://www.diodes.com/destools/calculators.html that will help with component selection.
INDUCTOR/FREQUENCY SELECTION
Recommended inductor values for the ZXLD1374 are in the range 22 H to 100 H. The chosen coil should have a saturation current higher than the peak sensed current and a continuous current rating above the required mean sensed current by at least 50%. The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended limits over the supply voltage and load current range. The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz ~ 400kHz in most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs or the input voltage increases. The graphs below can be used to select a recommended inductor to maintain the ZXLD1374 switching frequency within a predetermined range when used in different topologies.
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ZXLD1374 Applications Information (Continued)
INDUCTOR/FREQUENCY SELECTION
15 13
NEW PRODUCT
Number of LEDs
11 9 L=47uH 7 5 L=33uH 3 1 0 L=10uH 10 L=22uH 20 30 Supply Voltage (V) 40 50 60
Figure 32: 1.5A Buck mode inductor selection for target frequency of 400 kHz
15 13 Number of LEDs 11 9 7 5 L=33uH 3 L=10uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH L=47uH
Figure 33: 1.5A Buck mode inductor selection for target frequency > 500kHz
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ZXLD1374 Applications Information (Continued)
For example, in a Buck configuration (VIN =24V and 6 LEDs), with a load current of 1.5A; if the target frequency is around 400 kHz, the Ideal inductor size is L= 33H. The same kind of graphs can be used to select the right inductor for a Buck configuration and a LED current of 750mA, as shown in figures 34 and 35.
15
NEW PRODUCT
13 Number of LEDs 11 9 7 5 L=68uH 3 L=33uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH L=100uH
Figure 34: 750mA Buck mode inductor selection for target frequency 400kHz
15 13 Number of LEDs 11 9 7 5 L=33uH 3 L=10uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH L=47uH
Figure 35: 750mA Buck mode inductor selection for target frequency > 500kHz ZXLD1374
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ZXLD1374 Applications Information (Continued)
In the case of the Buck-boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 36) or higher than 500kHz (figure 37).
15 13
NEW PRODUCT
Number of LEDs
11 9 7 5 L=33uH 3 L=22uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH
Figure 36: 350mA Buck-boost mode inductor selection for target frequency 400kHz
15 13 Number of LEDs 11 9 7 5 3 L=22uH 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=33uH L=47uH
Figure 37: 350mA Buck-boost mode inductor selection for target frequency > 500kHz
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ZXLD1374 Applications Information (Continued)
For example, in a Buck-boost configuration (VIN =10-18V and 4 LEDs), with a load current of 350mA; if the target frequency is around 400kHz, the Ideal inductor size is L= 33uH. The same size of inductor can be used if the target frequency is higher than 500kHz driving 6LEDs with a current of 350mA from a VIN =12-24V. In the case of the Boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 38) or higher than 500kHz (figure 39).
15
L=47uH
NEW PRODUCT
13 Number of LEDs 11 9 7 5 3 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH
L=33uH
Figure 38: 350mA Boost mode inductor selection for target frequency 400kHz
L=47uH 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=22uH L=33uH
Figure 39: 350mA Boost mode inductor selection for target frequency > 500kHz ZXLD1374
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ZXLD1374 Applications Information (Continued)
Suitable coils for use with the ZXLD1374 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range manufactured by NIC components. The following websites may be useful in finding suitable components www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de
DIODE SELECTION
NEW PRODUCT
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the maximum LX voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX pin. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin, including supply ripple, does not exceed the specified maximum value. *A suitable Schottky diode would be PDS3100 (Diodes Inc).
OUTPUT CAPACITOR
An output capacitor may be required to limit interference or for specific EMC purposes. For Boost and Buck-boost regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first switching subinterval. An output capacitor in a Buck topology will simply reduce the LED current ripple below the inductor current ripple. In other words, this capacitor changes the current waveform through the LED(s) from a triangular ramp to a more sinusoidal version without altering the mean current value. In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to be less than 40% of the average LED current).
Buck:
C OUTPUT = 8 x fSW IL -PP x rLED x ILED-PP
Boost and Buck-boost
COUTPUT =
where: * * * * IL is the ripple of the inductor current, usually 20% of the average sensed current ILED is the ripple of the LED current, it should be <40% of the LEDs average current fsw is the switching frequency (from graphs and calculator) rLED is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the datasheet of the LED manufacturer).
D x ILED fSW x rLED x ILED -PP
The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. The minimum RMS current for the output capacitor is calculated as follows:
Buck
ICOUTPUT - RMS =
ILED -PP 12
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ZXLD1374 Applications Information (Continued)
Boost and Buck-boost
ICOUTPUT-RMS = ILED
DMAX 1 - DMAX
Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and performance over the voltage and temperature ranges.
BOOTSTRAP CIRCUIT
NEW PRODUCT
In Boost and Buck-boost modes with input voltages below 12V to fully enhance the internal power switch it is required to use a bootstrap network as shown in figure 40.
Figure 40: Bootstrap circuit for low voltage operations
The bootstrap circuit is realized by adding a reservoir capacitor, C8, current limiting resistor R13 (=100) and a blocking diode D2 (DFSL160). During the power switch turn-on C8 needs to be able to supply approximately 10mA current. A capacitor of 1uF (C8) provides a reasonable trade-off between VAUX supply needs and LED current accuracy. At start-up the VAUX pin requires only a few mA of current from the LED current. In normal operation the current taken from the LED current to supply VAUX will be negligible.
INPUT CAPACITOR
The input capacitor and minimum RMS current for the output capacitor can be calculated knowing the input voltage ripple VIN-PP as follows:
Input capacitor Buck
CIN = D x(1 - D)x ILED fSW x VIN-PP
Minimum RMS current
ICIN-RMS = ILED x Dx(1 - D)
use D=0.5 as worst case
use D=0.5 as worst case
Boost
CIN = ICOIL - PP 8 x fSW x VIN - PP ICIN-RMS = IL -PP 12
Buck-boost
CIN = D x ILED fSW x VIN-PP
ICIN-RMS = ILED x D (1 - D)
Use D = DMAX as worst case
Use D = DMAX as worst case
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ZXLD1374 Applications Information (Continued)
PWM OUTPUT CURRENT CONTROL & DIMMING
The ZXLD1374 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with 1000:1 resolution; however higher dimming frequencies can be used - at the expense of dimming dynamic range and accuracy. Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is better than 1% for PWM from 5% to 100%. This is shown in the graph below:
15.0% 1500
NEW PRODUCT
12.5% Normalized LED current error VIN = 24V TA = 25C fPWM = 1kHz
1250
7.5% ILED 5.0%
750
500
2.5%
Normalized LED Current Error
250
0.0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% PWM duty cycle
0 100%
Figure 41. LED current linearity and accuracy with PWM dimming at 1kHz
For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater than 5%. This is shown in the graph below:
15.0% 1500
12.5% Normalized LED current error
1250
7.5%
750
5.0%
500
2.5% Normalized LED Current Error 0.0% 0% 10% 20% 30% 40% 50% 60% PWM duty cycle 70% 80% 90%
250
0 100%
Figure 42. LED current linearity and accuracy with PWM dimming at 100Hz
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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LED current (mA)
10.0%
VIN = 24V TA = 25C fPWM = 100Hz
ILED
1000
LED current (mA)
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1000
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ZXLD1374 Applications Information (Continued)
The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector transistor. In this case the designer can either use the internal pull-up network or an external pull-up network in order to speed-up PWM transitions, as shown in the Boost/ Buck-boost section.
NEW PRODUCT
Figure 43. PWM Dimming from Open Collector Switch
Figure 44. PWM Dimming from MCU
LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the PWM pin to turn the controller on and off. This will produce an average output current proportional to the duty cycle of the control signal. During PWM operation, the device remains powered up and only the output switch is gated by the control signal. The PWM signal can achieve very high LED current resolution. In fact, dimming down from 100% to 0, a minimum pulse width of 5us can be achieved resulting in very high accuracy. While the maximum recommended pulse is for the PWM signal is10ms.
Figure 45. PWM Dimming Minimum and Maximum Pulse
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ZXLD1374 Applications Information (Continued)
The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the circuitry inside the device is switched off and residual quiescent current will be typically 90A. In particular, the Status pin will go down to GND while the FLAG and REF pins will stay at their nominal values.
NEW PRODUCT
Fig 46. Stand-by state from PWM signal TADJ pin - Thermal control of LED current
The `Thermal control' circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on the TADJ pin to 625mV at the required temperature threshold. This will give 100% LED current below the threshold temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the value of Rth and/or the thermistor to suit the requirements of the chosen LED. The Thermal Control feature can be disabled by connecting TADJ to REF. Here is a simple procedure to design the thermal feedback circuit: 1. Select the temperature threshold TTHRESHOLD at which the current must start to decrease 2. Select the Thermistor TH1 (both resistive value at 25C and beta) 3. Select the value of the resistor RTH as RTH = TH1 at TTHRESHOLD
Figure 47. Thermal feedback network
For example, 1) 2) 3) Temperature threshold TTHRESHOLD = 70C TH1 = 10k at 25C and beta= 3500 RTH = TH1 at TTHRESHOLD = 3.3k TH1 = 3.3k at 70C
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information (Continued)
Over-Temperature Shutdown
The ZXLD1374 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125C nominal and the output is disabled when die temperature exceeds 150C nominal. Normal operation resumes when the device cools back down to 125C.
FLAG/STATUS Outputs
NEW PRODUCT
The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output, which is normally high resistance, but switches low resistance to indicate that a warning, or fault condition exists. STATUS is a DAC output, which is normally high (4.5V), but switches to a lower voltage to indicate the nature of the warning/fault. Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table:
Table 2 Warning/Fault condition Severity (Note 10) Monitored parameters FLAG Nominal STATUS voltage
Normal operation Supply under-voltage Output current out of regulation (Note 11) Driver stalled with switch `on', or `off' (Note 12) Switch over-voltage Device temperature above maximum recommended operating value Sense resistor current IRS above specified maximum Average switch current greater than 1.5A
Notes:
H 1 2 2 2 3 4 5 5 VAUX<5.6V VIN<5.6V VSHP outside normal voltage range tON, or tOFF>100s LX voltage > 60V TJ>125C VSENSE>0.375V ILX > 1.5A L L L L L L L L
4.5 4.5 3.6 3.6 3.6 2.7 1.8 0.9 0.9
10. Severity 1 denotes lowest severity. 11. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able to maintain regulation. 12. This warning will be indicated if the LX pin stays at the same level for greater than 100us (e.g. the internal transistor cannot pass enough current to reach the upper switching threshold).
ZXLD1374
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ZXLD1374 Applications Information (Continued)
FLAG VOLTAGE
VR EF
0V
4.5V
NEW PRODUCT
Normal Operations
3.6V
VAUX UVLO
STAT US VOLTA GE
- VI N UVLO - STALL - OU T of REG
2.7V
ZXLD1374 Switch OV
1.8V
Over Temperature
0.9V
Over C urrent 0A 0 1 2 SEVERITY 3 4 5
Fig 48. Status levels
In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g. `Excessive coil current' and `Out of regulation' occurring together will produce an output of 0.9V on the STATUS pin. If VADJ>1.7V, VSENSE may be greater than the excess coil current threshold in normal operation and an error will be reported. Hence, STATUS and FLAG are only guaranteed for VADJ<=VREF. Diagnostic signals should be ignored during the device start - up for 100s. The device start up sequence will be initiated both during the first power on of the device or after the PWM signal is kept low for more than 15ms, initiating the standby state of the device. In particular, during the first 100s the diagnostic is signaling an over-current then an out-of-regulation status. These two events are due to the charging of the inductor and are not true fault conditions.
VREF FLAG
Out of regulation STATUS Overcurrent
1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 time (s) 120 140 160 180 200
Coil current (A)
Figure 49. Diagnostic during Start-Up ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information (Continued)
Over-voltage Protection
The ZXLD1374 is inherently protected against open-circuit load when used in Buck configuration. However care has to be taken with open-circuit load conditions in Buck-boost or Boost configurations. This is because in these configurations there is only an over-voltage FLAG but no internal open-circuit protection mechanism for the internal MOSFET. In this case an Over-Voltage-Protection (OVP) network should be provided to the MOSFET to avoid damage due to open circuit conditions. This is shown in Figure 37 below, highlighted in the dotted blue box.
NEW PRODUCT
Figure 50. OVP Circuit
The zener voltage is determined according to: Vz = VLEDMAX +10%. The LX pin voltage exceeds Vz then the gate of MOSFET Q2 will start to turn on causing the PWM pin to be brought low. This will disable to LX output until the voltage on the LX falls below Vz. If the fault exists for longer than 20ms then the ZXLD1374 will enter into a shutdown state.
Take care of the max voltage drop on the Q2 MOSFET gate. Alternatively, to perform the OVP function, it can be used the diagnostic section of the ZXLD1374. In particular a microcontroller can read the FLAG and the status pins, and if they signal an over-voltage, the microcontroller can switch the device off by pulling the PWM signal low.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Information (Continued)
PCB Layout considerations
PCB layout is a fundamental activity to get the most of the device in all configurations. In the following section it is possible to find some important insight to design with the ZXLD1374 both in Buck and Buck-boost/Boost configurations.
NEW PRODUCT
Figure 51. Circuit Layout
Here are some considerations useful for the PCB layout: In order to avoid ringing due to stray inductances, the inductor L1, the anode of D1 and the LX pin should be placed as close together as possible. The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more than 5mm from the SHP pin. Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of 2.2uF, X7R, 100V (C3 and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of 1uF, X7R, 100V each (C2, C8), as well as a further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9) the device is used in Buck mode, or can be driven from a separate supply.
ZXLD1374
Document number: DS35032 Rev. 1 - 2
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ZXLD1374 Applications Examples
1.5A Buck LED driver
NEW PRODUCT
In this application example, ZXLD1374 is connected as a Buck LED driver with schematic and parts list shown below. The LED driver is able to deliver 1.5A of LED current to single or multiple LEDs in series with input voltage ranged from 10V to 50V. In order to achieve high efficiency under high LED current, Super Barrier Rectifier (SBR) with low forward voltage is used as free wheeling rectifier. With only a few extra components, the ZXLD1374 LED driver is able to deliver LED power of greater than 60W. This is suitable for applications which require high LED power likes high power down lighting, wall washer, automotive LED lighting etc.
Figure 52. Application circuit of 1.5A Buck LED driver Bill of Material Ref No.
U1 D1 L1 C1 C2 C3 C4 C5 R1 R2 R3
Value
60V 1.5A LED driver 100V 3A SBR 33uH 4.2A 100pF 50V 1uF 100V X7R 2.2uF 100V X7R 300m 1% 4.7
Part No.
ZXLD1374 SBR3U100 744770933 SMD 0805/0603 SMD1206 SMD1210 SMD1206 SMD1206
Manufacturer
Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic
Typical Performance
Efficiency vs Input Voltage
100% 90% 80%
LED Current vs Input Voltage
1600
Efficiency (%)
70% 60% 50% 40% 30% 20% 10% 0% 10 15 20 25 30 35 40 45 50
LED Current (mA)
1200
800
1 LED VF=3.4V 3 LED VF=9.8V 5 LED VF=16V
400
1 LED VF=3.4V 3 LED VF=9.8V 5 LED VF=16V
0 10 15 20 25 30 35 40 45 50
Input Voltage (V)
Input Voltage (V)
Figure 53. Efficiency
Figure 54. Line regulation
ZXLD1374
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ZXLD1374 Applications Examples
350mA Boost LED diver
In this application example, ZXLD1374 is connected as a Boost LED driver with schematic and parts list shown below. The LED driver is able to deliver 350mA of LED current into 12 high brightness LED with input voltage ranged from 16V to 28V.
NEW PRODUCT
Overall high efficiency of 92%+ make it ideal for applications likes solar LED street lighting and general LED illuminations.
Figure 55. Application circuit of 350mA Boost LED driver Bill of Material
Ref No. U1 Q1 D1 Z1 L1 C1 C3 C4 C2 R1 R2 R3 R4 R5 Value 60V LED driver 60V MOSFET 100V 3A Schottky 51V 410mW Zener 47uH 2.6A 100pF 50V 4.7uF 100V X7R 1uF 50V X7R 300m 1% 120k 1% 36k 1% 2.7k
Efficiency vs Input Voltage
100% 90% 80%
300 400 350
Part No. ZXLD1374 2N7002A PDS3100-13 BZT52C51 744771147 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603
Manufacturer Diodes Inc Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic
Generic Generic
LED Current vs Input Voltage
Typical Performance
70%
LED Current
Efficiency
60% 50% 40% 30% 20% 10% 0% 16 18 20 22 24 26 28 30
250 200 150 100 50 0 16 18 20 22 24 26 28 30
12 LED VF=37V 15 LED VF=47V
12 LED VF=37V 15 LED VF=47V
Input Voltage
Input Voltage
Figure 56. Efficiency
Figure 57. Line regulation
ZXLD1374
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ZXLD1374 Applications Examples
350mA Buck-boost LED driver
NEW PRODUCT
In this application example, ZXLD1374 is connected as a Buckboost LED driver with schematic and parts list shown below. The LED driver is able to deliver 350mA of LED current into 4/5 high brightness LED with input voltage ranged from 7V to 20V. In order to increase the driving voltage level for the internal MOSFET during low voltage input, bootstrap circuit formed by R6 D2 and C6 are used to supply higher voltage to the VAUX pin. Since the Buck-boost LED driver can handle an input voltage range below and above the LED voltage, this versatile input voltage range makes it ideal for automotive lighting applications.
Figure 58. Application circuit of 350mA Buck-boost LED driver
Bill of Material
Ref No. U1 Q1 D1 D2 Z1 L1 C1 C3 C4 C5 C2 C6 R1 R2 R3 R4 R5 R6 Value 60V LED driver 60V MOSFET 100V 3A Schottky 100V 1A Schottky 47V 410mW Zener 47uH 2.6A 100pF 50V 4.7uF 50V X7R 1uF 50V X7R 300m 1% 120k 1% 36k 1% 2.7k 1k Part No. ZXLD1374 2N7002A PDS3100-13 B1100 BZT52C47 744771147 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 SMD 1206 Manufacturer Diodes Inc Diodes Inc Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Generic Generic Generic
Typical Performance
Efficiency vs Input Voltage
100% 90% 80% 70%
LED Current vs Input Voltage
400 350 300
Efficiency
60% 50% 40% 30% 20% 10% 0% 7 8 9 10 11 12 13 14 15 16 17 18 19 20
LED Current
250 200 150 100
4 LED VF=12.5V 5 LED VF=15.6V
50 0 7 8 9 10 11 12 13 14 15 16
4 LED VF=12.5V 5 LED VF=15.6V
17 18 19 20
Input Voltage
Input Voltage
Figure 59. Efficiency ZXLD1374
Document number: DS35032 Rev. 1 - 2
Figure 60. Line regulation
Page 33 of 35 www.diodes.com October 2010
(c) Diodes Incorporated
A Product Line of Diodes Incorporated
ZXLD1374 Ordering Information
Device Packaging Status Part Marking ZXLD1374 Reel Quantity 2500 Tape Width Reel Size
ZXLD1374EST20TC
TSSOP-20EP
Active
16mm
13"
Package Mechanical Data
TSSOP-20 EP
NEW PRODUCT
1
ZXLD1374
Document number: DS35032 Rev. 1 - 2
Page 34 of 35 www.diodes.com
October 2010
(c) Diodes Incorporated
A Product Line of Diodes Incorporated
ZXLD1374
IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website, harmless against all damages.
NEW PRODUCT
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel. Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application. Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks. LIFE SUPPORT Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systemsrelated information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright (c) 2010, Diodes Incorporated www.diodes.com
ZXLD1374
Document number: DS35032 Rev. 1 - 2
Page 35 of 35 www.diodes.com
October 2010
(c) Diodes Incorporated

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