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| A Product Line of Diodes Incorporated ZXLD1370 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER Description The ZXLD1370 is an LED driver controller IC for driving external MOSFETs to drive high current LEDs. It is a multitopology controller 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 15 LEDs in series. The ZXLD1370 is a modified hysteretic controller using a patent pending control scheme providing high output current accuracy in all three modes of operation. High accuracy dimming is achieved through DC control and high frequency PWM control. The ZXLD1370 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-16 EP Features * * * * * 0.5% typical output current accuracy 6 to 60V operating voltage range LED driver supports Buck, Boost and Buck-boost configurations 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 * * Typical Application Circuit Buck-boost diagram utilizing thermistor and Tadj Curve showing LED current vs. TLED ZXLD1370 Document number: DS32165 Rev. 2 - 2 1 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Pin Descriptions Pin Name Pin Type Description Adjust input (for dc output current control) Connect to REF to set 100% output current. Drive with dc voltage (125mV 1 I REF 2 O TADJ 3 I SHP 4 I/O STATUS 5 O SGND PGND N/C N/C GATE 6 7 8 9 10 P P - VAUX 11 P VIN ISM FLAG 12 13 14 P I O PWM 15 I GI 16 I EP Notes: PAD P . Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin. ZXLD1370 Document number: DS32165 Rev. 2 - 2 2 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated) Symbol VIN VAUX VISM VSENSE VGATE IGATE VFLAG VPWM, VADJ, VTADJ, VGI, VPWM 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) Gate driver output voltage Gate driver continuous output current Flag output voltage Other input pins 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 20 18 -0.3 to 40 -0.3 to 5.5 150 -55 to 150 Unit V V V V V mA V V C C 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. Recommended Operating Conditions Symbol VIN VAUX VISM VSENSE VADJ IREF fmax VTADJ fPWM tPWMH/L VPWMH VPWML TJ GI Notes: Parameter Input supply voltage range Auxiliary supply voltage range (Note 2) Current sense monitor input range Differential input voltage External dc control voltage applied to ADJ pin to adjust output current Reference external load current Recommended switching frequency range (Note 3) Temperature adjustment (TADJ) input voltage range Recommended PWM dimming frequency range (Note 4) PWM pulse width in dimming mode 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 Performance/Comment Normal operation Functional (Note 1) Normal operation Functional VVIN-VISM, with 0 VADJ 2.5 DC brightness control mode from 10% to 200% REF sourcing current Min 8 6.3 8 6.3 6.3 0 0.125 Max 60 60 60 450 2.5 1 Unit V V V mV V mA kHz V Hz Hz ms V V C 300 0 To achieve 1000:1 resolution To achieve 500:1 resolution PWM input high or low 100 100 0.002 2 0 -40 0.20 1000 VREF 500 1000 10 5.5 0.4 125 0.50 Ratio= VGI/VADJ 1. 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 6V and 8V, depending upon load and conditions. 2. 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. 3. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency are not tested in production. 4. This gives maximum resolution at the expense of accuracy. To ensure accuracy the following equation should be used: 2*Resolution *fPWM < fSWH ZXLD1370 Document number: DS32165 Rev. 2 - 2 3 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Electrical Characteristics (Test conditions: VIN = VAUX = 12V, TA = 25C, unless otherwise specified.) 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. Internal reference voltage VREF Change in reference voltage with output VREF current 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 100 A Min 5.2 5.5 Typ 5.6 6 1.5 150 90 0.7 1.25 Max 6.3 6.5 3 300 150 10 1.263 5 Units V V mA A A A V mV dB ppm/C 1.237 -5 -60 VREF_LINE Reference voltage line regulation VIN = VAUX , 6.5V -90 +/-50 1.25 2.5 100 5 0.8 100 5 36 100 25 0.125 V nA A V nA A A ms C C 10 15 150 125 11 0.25 300 350 20 2 375 A % mV The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This provides some failsafe should those pins get overdriven. ZXLD1370 Document number: DS32165 Rev. 2 - 2 4 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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 6) VIN under-voltage (VIN < 5.6V) Switch stalled (tON or tOFF> 100s) Over-temperature (TJ > 125C) Excess sense resistor current (VSENSE > 0.32V) Normal operation No load Sourcing 1mA (Note 7) Sinking 1mA, (Note 8) VIN = VAU X= VISM = 18V IGATE = 1mA Charging or discharging gate of external switch with QG = 10nC and 400kHz Min Typ Max 0.5 1 4.8 3.9 3.9 3.9 2.1 1.2 Units V A 4.2 3.3 3.3 3.3 1.5 0.6 4.5 3.6 3.6 3.6 1.8 0.9 10 STATUS Flag no-load output voltage VSTATUS (Note 5) V RSTATUS Output impedance of STATUS output Driver output (PIN GATE) VGATEH High level output voltage VGATEL Low level output voltage k V 0.5 V V mA 10 11 VGATECL High level GATE CLAMP voltage IGATE Dynamic peak current available during rise or fall of output voltage 12.8 300 15 Time to assert `STALL' flag and warning on STATUS output GATE low or high (Note 9) LED Thermal control circuit (TADJ) parameters Upper threshold voltage Onset of output current reduction VTADJH (VTADJ falling) Lower threshold voltage Output current reduced to <10% of VTADJL set value (VTADJ falling) TADJ pin Input current ITADJ VTADJ = 1.25V tSTALL Notes: 100 170 s 560 380 625 440 690 500 1 mV mV A 5. 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. 6. Flag is asserted if VSHP<2.5V or VSHP>3.5V 7. GATE is switched to the supply voltage VAUX for low values of VAUX (i.e. between 6V and approximately 12V). For VAUX>12V, GATE is clamped internally to prevent it exceeding 15V. 8. GATE is switched to PGND by an NMOS transistor 9. If tON exceeds tSTALL, the device will force GATE low to turn off the external switch and then initiate a restart cycle. 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. ZXLD1370 Document number: DS32165 Rev. 2 - 2 5 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Typical Characteristics - Buck Mode - RS = 150m - L = 33H - ILED = 1.5A 1.500 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs 1.490 1.480 1.470 1.460 1.450 1.440 1.430 6.5 LED Current (A) 11 15.5 29 33.5 38 42.5 47 51.5 Input Voltage (V) Figure 1: Load Current vs. Input Voltage & Number of LED 20 24.5 56 60.5 1000 1 LE D 3 LE Ds 5 LE Ds 7 LE Ds 9 LE Ds 11 LE Ds 13 LE Ds 15 LE Ds 900 Switching Frequency (kHz) 800 700 600 500 400 300 200 100 0 6.5 TA = 25C VAU X = VIN 11 15.5 29 33.5 38 42.5 47 51.5 Input Voltage (V) Figure 2: Frequency vs. Input Voltage & Number of LED 20 24.5 56 60.5 100% 95% 90% Efficiency 85% 80% 75% 70% 65% 60% 6.5 11 15.5 20 29 33.5 38 42.5 47 Input Voltage (V) Figure 3: Efficiency vs. Input & Number of LED 24.5 51.5 56 60.5 ZXLD1370 Document number: DS32165 Rev. 2 - 2 6 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Typical Characteristics - Buck Mode - Rs = 300m - L = 47H - ILED = 750mA 0.740 0.735 TA = 25C LED Current (A) V AUX = VIN 0.730 0.725 0.720 2 LEDs 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs 0.715 6.5 11 15.5 20 29 33.5 38 42.5 Input Voltage (V) Figure 4: I LED vs. Input & Number of LED 7 LEDs 9 LEDs 11 LEDs 13 LEDs 24.5 47 51.5 56 60.5 1000 2 LEDs 3 LEDs 5 LEDs 15 LEDs 900 Switching Frequency (kHz) 800 700 600 500 400 300 200 100 0 6.5 TA = 25C VAU X = VIN 11 15.5 29 33.5 38 42.5 47 Input Voltage (V) Figure 5: Frequency ZXLD1370 - Buck Mode - L47 H 20 24.5 51.5 56 60.5 100% 95% 90% Efficiency 85% 80% 75% 70% 2 LEDs 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs TA = 25C VAU X = VIN 65% 60% 6.5 11 15.5 29 33.5 38 42.5 47 Input Voltage (V) Figure 6: Efficiency vs. Input Voltage & Number of LED 20 24.5 51.5 56 60.5 ZXLD1370 Document number: DS32165 Rev. 2 - 2 7 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Typical Characteristics - Boost mode - ILED = 350mA - RS = 150m - GIRATIO = 0.23 0.400 0.350 0.300 TA = 25C VAU X = VIN LED Current (A) 0.250 0.200 0.150 0.100 0.050 3 LEDs 4 LEDs 6 LEDs 8 LEDs 10 LEDs 12 LEDs 14 LEDs 16 LEDs 0.000 6.5 10 13.5 17 24 27.5 31 34.5 38 Input Voltage (V) Figure 7: ILED vs. Input Voltage & Number of LED 6 LEDs 8 LEDs 10 LEDs 12 LEDs 20.5 41.5 45 48.5 500 3 LEDs 4 LEDs 14 LEDs 16 LEDs 450 Switching Frequency (kHz) 400 350 300 250 200 150 100 50 6.5 TA = 25C VAU X = VIN Boosted voltage across LEDs approaching VIN 10 13.5 24 27.5 31 34.5 38 41.5 Input Voltage (V) Figure 8: Frequency vs. Input Voltage & Number of LED 6 LEDs 8 LEDs 10 LEDs 12 LEDs 14 LEDs 17 20.5 45 48.5 100% 95% 90% 85% 80% 75% 70% 65% 60% 6.5 3 LEDs 4 LEDs 16 LEDs Efficiency TA = 25C VAU X = VIN 10 13.5 24 27.5 31 34.5 38 41.5 Input Voltage (V) Figure 9: Efficiency vs. Input Voltage & Number of LED 17 20.5 45 48.5 ZXLD1370 Document number: DS32165 Rev. 2 - 2 8 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Typical Characteristics - Buck-Boost mode - RS=150m - ILED = 350mA - GIRATIO = 0.23 0.370 3 LEDs 4 LEDs 5 LEDs 6 LEDs 7 LEDs 8 LEDs 0.365 0.360 LED Current (A) 0.355 0.350 0.345 0.340 0.335 0.330 6.5 8 11 12.5 14 Input Voltage (V) Figure 10: LED Current vs. Input Voltage & Number of LED 4 LEDs 5 LEDs 6 LEDs 7 LEDs 9.5 15.5 17 800 3 LEDs 8 LEDs 700 Switching Frequency (kHz) 600 500 400 300 200 100 0 6.5 8 11 12.5 14 15.5 Input Voltage (V) Figure 11: Switching Frequency vs. Input Voltage & Number of LED 4 L EDs 5 L EDs 6 L EDs 7 L EDs 8 L EDs 9.5 17 100% 3 L EDs 95% 90% Efficiency 85% 80% 75% 70% 65% 60% 6.5 8 11 12.5 14 Input Voltage (V) Figure 12: Efficiency vs. Input Voltage & Number of LED 9.5 15.5 17 ZXLD1370 Document number: DS32165 Rev. 2 - 2 9 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Applications Information The ZXLD1370 is a high accuracy hysteretic inductive buck/boost/buck-boost controller designed to be used with an external NMOS switch 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 13 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 external NMOS switch transistor M1 via the internal Gate Driver. 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 GATE goes low, 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, GATE goes high, the switch is turned on again and the cycle of events repeats, resulting in continuous oscillation. Figure 13: Buck configuration 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 30%), the frequency may deviate from nominal in extreme conditions. Loop compensation is achieved by a single external capacitor C2, connected between SHP and SGND. Gate Voltage ~15V 0V V VIN V -225 mV VIN ISM Voltage Coil/LED current 225mV/R s 0A t t OFF ON Figure 14: Operating waveforms (Buck mode) ZXLD1370 Document number: DS32165 Rev. 2 - 2 10 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 b) Boost and Buck-Boost modes 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 external NMOS switch transistor M1 via the internal Gate Driver. 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 GATE goes low, 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, GATE goes high, 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 Figure 15: Boost and Buck-Boost configuration 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 minimises variation in output current with changes in operating conditions. Loop compensation is achieved by a single external capacitor C2, connected between SHP and SGND. Gate Voltage ~15V 0V VVIN VVIN -225mV ISM Voltage Coil current 225mV/Rs 0A LED current 225mV/Rs Average LED current 0A tOFF tON Figure 16 - Operating waveforms (Boost and Buck-boost modes) Note: In Boost and Buck-boost modes, average ILED= average ICOIL x RGI1/(RGI1+RGI2) 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. ZXLD1370 Document number: DS32165 Rev. 2 - 2 11 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Application Information A basic ZXLD1370 application circuit is shown in Figure 13 and 15. 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, the inductor/frequency setting and the MOSFET selection. 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 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 giving the ratio of average LED current (ILED) to average sense resistor/coil current (IRS). RS VIN ISM ILED = IRs = 225mV VADJ R S VREF REF If the ADJ and GI pins are connected to VREF directly, this becomes: ADJ ILED Therefore: = IRs = 225mV RS GI SGND Rs = 225mV ILED Figure 17: Buck configuration RS 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 (IRS). VIN ISM REF ILED = VGI R GI1 IRs = IRs VADJ (R GI1 + R GI2 ) 225mV VADJ RS VREF ADJ R GI2 GI Where IRs = R GI1 SGND When the ADJ pin is connected to VREF directly, this becomes: IRs = 225mV RS 12 of 33 www.diodes.com Figure 18: Boost and Buck-boost connection ZXLD1370 Document number: DS32165 Rev. 2 - 2 May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Therefore: Rs = R GI1 225mV (R GI1 + R GI2 ) 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 ZXLD1370, the recommended potential divider ratio is given by: 0. 2 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 = Boost mode VLEDs VINMIN VLEDS - VIN MIN VLEDS DMAX = Buck-boost mode DMAX = VLEDS VLEDS + VIN MIN Set the appropriate GI ratio according to the circuit duty and the max switch current admissible cycle limitations VGI R GI1 = 1 - D MAX VADJ (R GI1 + R GI2 ) - Set RGI1 as: - Calculate RGI2 as: 10k R GI1 200k R GI2 - D MAX x R GI1 1 - D MAX Calculate the sense resistor as: 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. 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: ZXLD1370 Document number: DS32165 Rev. 2 - 2 13 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ILED VGI RGI1 = = 0.23 IRS VADJ (RGI1 + RGI2) Setting RGI1= 33k it results R GI2 = R GI1( VADJ - 1) = 110k VGI 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 GI ratio 0.2 0.25 0.3 0.35 0.4 0.45 0.5 RGI1 30k 33k 39k 30k 100k 51k 30k RG2 120k 100k 91k 56k 150k 62k 30k INDUCTOR/FREQUENCY SELECTION Recommended inductor values for the ZXLD1370 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 ZXLD1370 switching frequency within a predetermined range when used in different topologies. Buck inductor selection: ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor Target Switching frequency - 400kHz 15 13 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 19: 1.5A Buck mode inductor selection for target frequency of 400 kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 14 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor Target Switching frequency > 500kHz 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 20: 1.5A Buck mode inductor selection for target frequency > 500kHz 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 21 and 22. ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor Target Switching frequency 400kHz 15 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 21: 750mA Buck mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 15 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor Target Switching frequency > 500kHz 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 30 Supply Voltage (V) 40 50 60 L=47uH L=33uH L=68uH L=100uH Figure 22: 750mA Buck mode inductor selection for target frequency > 500kHz 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 23) or higher than 500kHz (figure 24). ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency - 400kHz 15 13 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 23: 350mA Buck-Boost mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 16 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency > 500kHz 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 24: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz For example, in a Buck-bust 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 25) or higher than 500kHz (figure 26). ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency - 400kHz 15 13 Number of LEDs 11 9 7 5 3 1 0 10 20 L=22uH L=47uH L=33uH 30 Supply Voltage (V) 40 50 60 Figure 25: 350mA Boost mode inductor selection for target frequency 400kHz ZXLD1370 Document number: DS32165 Rev. 2 - 2 17 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency > 500kHz 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 26: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz Suitable coils for use with the ZXLD1370 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 MOSFET Selection The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node. The current rating is recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the resistive and switching power losses. P = Presistive + Pswitching Resistive power losses The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance. Calculate the current for the different topologies as follows: Buck mode IMOSFET -MAX = D MAX x ILED Boost / Buck-boost mode IMOSFET -MAX = D MAX x ILED 1 - DMAX The approximate RMS current in the MOSFET will be: Buck mode IMOSFET -RMS =ILED D Boost / Buck-boost mode IMOSFET -RMS = D x ILED 1- D 18 of 33 www.diodes.com May 2010 (c) Diodes Incorporated ZXLD1370 Document number: DS32165 Rev. 2 - 2 A Product Line of Diodes Incorporated ZXLD1370 The resistive power dissipation of the MOSFET is: Presistive = IMOSFET-RMS x RDS -ON 2 Switching power losses Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using a first order rough approximation, the switching power dissipation of the MOSFET is: Pswitching = CRSS x V 2 IN x fsw x ILOAD IGATE where CRSS is the MOSFET's reverse-transfer capacitance (a data sheet parameter), fSW is the switching frequency, IGATE is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold. Matching the MOSFET with the controller is primarily based on the rise and fall time of the gate voltage. The best rise/fall time in the application is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit inductance, switching frequency, etc. How fast a MOSFET can be turned on and off is related to how fast the gate capacitance of the MOSFET can be charged and discharged. The relationship between C (and the relative total gate charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as: dt = dV C Qg = I I where dt = turn-on/turn-off time dV = gate voltage C = gate capacitance = Qg/V I = drive current - constant current source (for the given voltage value) Here the constant current source" I " usually is approximated with the peak drive current at a given driver input voltage. Example 1) Using the DMN6068 MOSFET (VDS(MAX) = 60V, ID(MAX) = 8.5A): QG = 10.3nC at VGS = 10V ZXLD1370 IPEAK = I GATE = 300mA dt = Qg IPEAK = 10.3nC = 35ns 300mA Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt f = 1/ tPERIOD = 1.43MHz This frequency is well above the max frequency the device can handle, therefore the DNM6068 can be used with the ZXLD1370 in the whole spectrum of frequencies recommended for the device (from 300kHz to 1MHz). Example 2) Using the ZXMN6A09K (VDS(MAX) = 60V, ID(MAX) = 12.2A): QG = 29nC at VGS = 10V ZXLD1370 IPEAK = 300mA dt = Qg IPEAK = 29nC = 97ns 300mA Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt f = 1/ tPERIOD = 515kHz This frequency is within the recommended frequency range the device can handle, therefore the ZXMN6A09K is recommended to be used with the ZXLD1370 for frequencies from 300kHz to 500kHz). The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC. ZXLD1370 Document number: DS32165 Rev. 2 - 2 19 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Junction temperature estimation Finally, the ZXLD1370 junction temperature can be estimated using the following equations: Total supply current of ZXLD1370: IQTOT IQ + f * QG Where IQ = total quiescent current IQ-IN + IQ-AUX Power consumed by ZXLD1370 PIC = VIN * (IQ + f * Qg) Or in case of separate voltage supply, with VAUX < 15V PIC = VIN * IQ-IN + Vaux * (IQ-AUX + f * Qg) TJ = TA + PIC * RTH(JA)= TA + PIC * (RTH(JC)+ RTH(CA)) Where the total quiescent current IQTOT consists of the static supply current (IQ) and the current required to charge and discharge the gate of the power MOSFET. Moreover the part of thermal resistance between case and ambient depends on the PCB characteristics. DIODE SELECTION 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 transistor 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 Drain of the external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the Drain of the external MOSFET, 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 C OUTPUT = where: * * * * fSW D x ILED -PP x rLED x ILED -PP 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). 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: ZXLD1370 Document number: DS32165 Rev. 2 - 2 20 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Buck ICOUTPUT - RMS = ILED -PP 12 D MAX 1 - D MAX Boost and Buck-boost ICOUTPUT -RMS = ILED 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. INPUT CAPACITOR The input capacitor can be calculated knowing the input voltage ripple VIN-PP as follows: Buck CIN = Boost D x(1 - D)x ILED fSW x VIN-PP IL -PP 8 x fSW x VIN-PP D x ILED fSW x VIN-PP Use D = 0.5 as worst case CIN = Buck-boost CIN = Use D = DMAX as worst case The minimum RMS current for the output capacitor is calculated as follows: Buck ICIN-RMS = ILED x Dx(1 - D) Boost use D=0.5 as worst case ICIN-RMS = Buck-boost IL -PP 12 ICIN-RMS = ILED x D (1 - D) Use D=DMAX as worst case PWM OUTPUT CURRENT CONTROL & DIMMING The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with up to 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: ZXLD1370 Document number: DS32165 Rev. 2 - 2 21 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Buck m ode - L=33uH - Rs = 150m - PW @ 1kHz M 1500.00 1250.00 LED current [mA] 1000.00 750.00 500.00 250.00 0.00 0 10 20 30 40 50 PWM PWM @ 1kHz Error 60 70 80 90 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0% 100 Error Error Figure 27: 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: Buck m ode - L=33uH - Rs = 150m - PW @ 100Hz M 1500.00 1250.00 LED current [mA] 1000.00 750.00 500.00 250.00 0.00 0 10 20 30 40 50 PWM PWM @ 100Hz Error 60 70 80 90 10% 9% 8% 7% 6% 5% 4% 3% 2% 1% 0% 100 Figure 28: LED current linearity and accuracy with PWM dimming at 100Hz 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. Figure 29: PWM dimming from open collector switch Figure 30: PWM dimming from MCU ZXLD1370 Document number: DS32165 Rev. 2 - 2 22 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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 2s can be achieved resulting in very high accuracy. While the maximum recommended pulse is for the PWM signal is10ms. 2s Gate < 10 ms 0V PWM < 10 ms 0V 2s Figure 31:PWM dimming minimum and maximum pulse 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. Fig 32: Stand-by state from PWM signal ZXLD1370 Document number: DS32165 Rev. 2 - 2 23 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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) 2) 3) Select the temperature threshold Tthreshold at which the current must start to decrease Select the Thermistor TH1 (both resistive value at 25C and beta) Select the value of the resistor Rth as Rth = TH at Tthreshold Figure 33: Thermal feedback network For example, 1) 2) 3) Temperature threshold Tthreshold = 70C TH1 = 10k at 25C and beta= 3500 Rth = TH at Tthreshold = 3.3k TH = 3.3k @ 70C Over-Temperature Shutdown The ZXLD1370 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. ZXLD1370 Document number: DS32165 Rev. 2 - 2 24 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 FLAG/STATUS Outputs The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output, which is normally off, but switches low 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 Normal operation Supply under-voltage Output current out of regulation (Note 10) Driver stalled with switch `on', or `off' (Note 11) Device temperature above maximum recommended operating value Sense resistor current IRS above specified maximum Notes: Severity (Note 9) 1 2 2 2 3 4 Monitored parameters VAUX<5.6V VIN<5.6V VSHP outside normal voltage range tON, or tOFF>100s TJ>125C VSENSE>0.32V FLAG H L L L L L L Nominal STATUS voltage 4.5 4.5 3.6 3.6 3.6 1.8 0.9 9. Severity 1 denotes lowest severity. 10. 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. 11. This warning will be indicated if the gate pin stays at the same level for greater than 100us (e.g. the output transistor cannot pass enough current to reach the upper switching threshold). FLAG VOLTAGE VREF 0V 4.5V Normal Operations 3.6V VAUX UVLO STATUS VOLTAGE - VIN UVLO - STALL - OUT of REG 2.7V 1.8V Over Temperature 0.9V Over Current 0A 0 1 2 SEVERITY 3 4 Fig 34: 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. ZXLD1370 Document number: DS32165 Rev. 2 - 2 25 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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 0V STATUS O ut of r e g u la t io n O ver C u rre n t 2 2 5 m V /R 1 Coil current 0A 100us Fig 35: Diagnostic during Start-up Boosting VAUX supply voltage in Boost and Buck-Boost mode When the input voltage is lower than 8V, the gate voltage will also be lower 8V. This means that depending on the characteristics of the external MOSFET, the gate voltage may not be enough to fully enhance the power MOSFET. This boosting technique is particularly important when the output MOSFET is operating at full current, since the boost circuit allows the gate voltage to be higher than 12V. This guarantees that the MOSFET is fully enhanced reducing both the power dissipation and the risk of thermal runaway of the MOSFET itself. An extra diode D2 and decoupling capacitor C3 can be used, as shown below in figure 36, to generate a boosted voltage at VAUX when the input supply voltage at VIN is below 8V. This enables the device to operate with full output current when VIN is at the minimum value of 6V. In the case of a low voltage threshold MOSFET, the bootstrap circuit is generally not required. Fig 36: Bootstrap circuit for Boost and Buck-boost low voltage operations The resistor R2 can be used to limit the current in the bootstrap circuit in order to reduce the impact of the circuit itself on the LED accuracy. The impact on the LED current is usually a decrease of maximum 5% compared to the nominal current value set by the sense resistor. The Zener diode D3 is used to limit the voltage on the VAUX pin to less than 60V. Due to the increased number of components and the loss of current accuracy, the bootstrap circuit is recommended only when the system has to operate continuously in conditions of low input voltage (between 6 and 8V) and high load current. Other circumstances such as low input voltage at low load current, or transient low input voltage at high current should be evaluated keeping account of the external MOSFET power dissipation. Over-voltage Protection ZXLD1370 Document number: DS32165 Rev. 2 - 2 26 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 The ZXLD1370 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 no internal open-circuit protection mechanism for the external MOSFET. In this case an Over-Voltage-Protection (OVP) network should be provided externally to the MOSFET to avoid damage due to open circuit conditions. This is shown in Figure 33 below, highlighted in the dotted blue box. Fig 37: OVP circuit The zener voltage is determined according to: Vz = VLEDMAX +10% Take care of the max voltage drop on the Q2 MOSFET gate. 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 ZXLD1370 both in Buck and Buck-Boost/Boost configurations. SHP pin Inductor, Switch and Freewheeling diode VIN / VAUX decoupling Figure 38: 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 drain of Q1 should be placed as close together as possible. ZXLD1370 Document number: DS32165 Rev. 2 - 2 27 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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). VIN and VAUX pins can be short-circuited when the device is used in buck mode, or can be driven from a separate supply. APPLICATION EXAMPLES Example 1: 2.8A Buck LED driver In this application example, the ZXLD1370 is connected as a buck LED driver. The schematic and parts list are shown below. The LED driver is able to deliver 2.8A of LED current with an input voltage range of 8V to 24V. In order to achieve high efficiency at high LED current, a Super Barrier Rectifier (SBR) with a low forward voltage is used as the free wheeling rectifier. This LED driver is suitable for applications which require high LED current such as LED projector, automatic LED lighting etc. Figure 39: Application circuit: 2.8A Buck LED driver Table 3: Bill of Material Ref No. U1 Q1 D1 L1 C1 C2 C3 C4 C5 R1 R2 R3 R4 R5 Value Part No. ZXLD1370 ZXMN6A09K SBR10U45SP5 744770933 SMD 0805/0603 SMD1206 SMD1210 SMD1206 SMD1206 SMD 0805/0603 Manufacturer Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Generic 60V LED driver 60V MOSFET 45V 10A SBR 33uH 4.2A 100pF 50V 1uF 50V X7R 4.7uF 50V X7R 300m 1% 400m 1% 0 ZXLD1370 Document number: DS32165 Rev. 2 - 2 28 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Typical Performance Efficiency vs Input Voltage 100% 90% 80% 2500 3000 LED Current vs Input Voltage LED Current (m A) 24 70% Efficiency (%) 2000 60% 50% 40% 30% 20% 10% 0% 10 12 14 16 18 20 22 1500 1 LED 2 LED 1000 500 0 10 12 14 16 18 20 22 24 Input Voltage (V) Input Voltage (V) Figure 40: Efficiency Example 2: 400mA Boost LED driver Figure 41: Line regulation In this application example, the ZXLD1370 is connected as a boost LED driver. The schematic and parts list are shown below. The LED driver is able to deliver 400mA of LED current into 12 high-brightness LEDs with an input voltage range of 16V to 32V. The overall high efficiency of 92%+ makes it ideal for applications such as solar LED street lighting and general LED illuminations. Figure 42: Application circuit - 400mA Boost LED driver ZXLD1370 Document number: DS32165 Rev. 2 - 2 29 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Table 4: Bill of Material Ref No. U1 Q1 Q2 D1 Z1 L1 C1 C3 C9 C2 R1 R2 R9 R10 R12 R15 Value 60V LED driver 60V MOSFET 60V MOSFET 100V 3A Schottky 47V 410mW Zener 68uH 2.1A 100pF 50V 4.7uF 50V X7R 1uF 50V X7R 560m 1% 33K 1% 0 2.7K Part No. ZXLD1370 ZXMN6A25G 2N7002A PDS3100-13 BZT52C47 744771168 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 Manufacturer Diodes Inc Diodes Inc Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Generic Generic Typical Performance Efficiency vs Input Voltage 100% 90% 80% 70% 450 400 350 300 LED Current vs Input Voltage Efficiency 60% LED Current 16 18 20 22 24 26 28 30 32 50% 40% 30% 20% 10% 0% 250 200 150 100 50 0 16 18 20 22 24 26 28 30 32 Input Voltage Input Voltage Figure 43: Efficiency Figure 44: Line regulation Example 3: 700mA Buck-Boost LED driver In this application example, the ZXLD1370 is connected as a buck-boost LED driver. The schematic and parts list are shown below. The LED driver is able to deliver 700mA of LED current into 4 high-brightness LEDs with an input voltage range of 7V to 20V. Since the Buck-boost LED driver handles an input voltage range from below and above the total LED voltage, the versatile input voltage range make it ideal for automotive lighting applications. ZXLD1370 Document number: DS32165 Rev. 2 - 2 30 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Figure 45: Application circuit - 700mA Buck-Boost LED driver Table 5: Bill of Material Ref No. U1 Q1 Q2 D1 Z1 L1 C1 C3 C9 C2 R1 R2 R3 R9 R10 R12 R15 Value 60V LED driver 60V MOSFET 60V MOSFET 100V 5A Schottky 47V 410mW Zener 22uH 2.1A 100pF 50V 4.7uF 50V X7R 1uF 50V X7R 300m 1% 33K 1% 15K 1% 0 2.7K Part No. ZXLD1370 ZXMN6A25G 2N7002A PDS5100-13 BZT52C47 744771122 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 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% 800 700 600 LED Current vs Input Voltage LED Current 60% 500 400 300 200 100 0 Efficiency 50% 40% 30% 20% 10% 0% 7 8 9 10 11 12 13 14 15 16 17 18 19 20 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Input Voltage Input Voltage Figure 46: Efficiency Figure 47: Line regulation 31 of 33 www.diodes.com May 2010 (c) Diodes Incorporated ZXLD1370 Document number: DS32165 Rev. 2 - 2 A Product Line of Diodes Incorporated ZXLD1370 Ordering Information Device ZXLD1370EST16TC Packaging TSSOP-16 EP Status Active Part Marking ZXLD1370 Reel Quantity 2500 Tape Width 16mm Reel Size 13" Package Thermal Data Thermal Resistance Junction-to-Case, JC Package TSSOP-16 EP 23 Unit C/W Package Thermal Data TSSOP-16 EP ZXLD1370 Document number: DS32165 Rev. 2 - 2 32 of 33 www.diodes.com May 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 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. 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 ZXLD1370 Document number: DS32165 Rev. 2 - 2 33 of 33 www.diodes.com May 2010 (c) Diodes Incorporated |
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