ZXLD1366EV2 User Guide Issue 2

ZXLD1366EV2 USER GUIDE
DESCRIPTION
The ZXLD1366EV2, Figure 1, is a PCB constructed using an aluminium base for evaluating the ZXLD1366 LED
driver with internal switch, in DFN3030-6 package [1]. The evaluation board can be used to drive an external choice
of LEDs; the total forward voltage across the LEDs depending on the number and type connected.
The operating voltage is nominally higher than 30V for the external LEDs, and can be raised to 60V maximum, which
will reduce the supply current.
Please refer to the Zetex ZXLD1360 and ZXLD1350 products for applications requiring input voltages lower than 30V.
The nominal current for the evaluation board is set at 1A with a 0.2 sense resistor, R1.
The 150µH inductor used in the circuit is based on a 30V nominal supply, which should be connected across +VIN
and GND pins.
Test point ‘ADJ’ provides a connection point for DC or PWM dimming and shutdown.
Note: The evaluation board does not have reverse polarity protection
Warning: with 1A output, the connected LED will be hot and very bright
Figure 1: ZXLD1366EV2 evaluation board
ZXLD1366 DEVICE DESCRIPTION
The ZXLD1366 is a continuous mode inductive driver both in a TSOT23-5 package and DFN633 package, for
driving one or more series connected LEDs efficiently from a voltage source higher than the LED voltage. The
device includes the output switch and a current sense circuit, which requires an external sense resistor to set the
nominal current up to 1A.
ZXLD1366 DEVICE FEATURES

Typical accuracy better than 0.8%

Enhanced thermal capability in DFN633 package

Drives one or more series-connected LEDs

LEDs up to 1A.

Internal 60V switch.

Wide input voltage: 7V to 60V.

Inherent open circuit LED protection.

Brightness control using DC or PWM.

Internal PWM filter.
DEVICE APPLICATIONS

LED flashlights.

High Power LED driving.

Low-voltage halogen replacement LEDs.

Automotive lighting.

Illuminated signs.
ZXLD1366EV2
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ZXLD1366EV2
ZXLD1366 Device Packages, Pin and Definitions
TSOT23-5, DFN3030-6 and SO-8EP package options
ZXLD1366DACTC Device Pin Definition
Name
Pin No
Description
LX
1
Drain of NDMOS switch.
GND
2, 5
Ground (0V).
ADJ
3
Internal voltage ref. pin (1.25V) :

Leave floating for normal operation.

Connect to GND to turn off output current.

Drive with a DC voltage (0.3V to 1.25V) or with a PWM signal to
adjust output current

Connect a capacitor from this pin to ground to set the soft-start
time.
ISENSE
4
Connect a sense resistor, Rs, from the ADJ pin to VIN to sense the nominal
output current. Nominal Iout = 0.2/ R1
VIN
6
Input voltage: 6V to 60V. Decouple to ground with a 100nF and a 10uF or
higher ceramic capacitor depending on the input voltage[1].
ORDERING INFORMATION
EVALBOARD ORDER NUMBER
ZXLD1366EV2
DEVICE ORDER NUMBER
ZXLD1366DACTC
ZXLD1366E5TA
ZXLD1366EN8TC
Please note: Evaluation boards are subject to availability and qualified leads.
ZXLD1366EV2 EVALUATION BOARD
REFERENCE DESIGN
The ZXLD1366EV2 is an evaluation board configured to be used with the ZXLD1366 in DFN3030-6 package, as in
Figure 2. The target application is a driver for one or more series-connected LEDs for luminaires in both commercial
and automotive applications.
The maximum operating voltage is 60V, and the nominal current is set at 1A with a 0.2 sense resistor R1. The
device operates in continuous mode at approximately 70kHz, with a 150µH inductor, when the system drives a single
LED.
An accurate way of determining the current, avoiding the need to insert an ammeter in the current path, is to measure
the voltage on the sense resistor. A 10K resistor and a 1uF capacitor can be used to form a low pass filter and the
voltage across the capacitor represents a more stable dc reading of current. Using this method, 200mV represents
1Amp when using a 0.2Ω sense resistor.
The ADJ pin connects to a low pass filter within the ZXLD1366 chip to provide some decoupling, but the external
capacitor C2 (100nF) is used to provide additional decoupling to reduce any high frequency noise as well as
enabling the soft start function.
Both DC and PWM dimming can be achieved by driving the ADJ pin. For DC dimming, the ADJ pin may be driven
between 0.3V and 1.25V. Driving the ADJ pin below 0.2V will shut down the output current. For PWM dimming, an
external open-collector NPN transistor or open-drain N-channel MOSFET can be used to drive the ADJ pin. The
PWM frequency can be low, around 100Hz to 1 kHz, or high between 10 kHz to 50 kHz.
ZXLD1366EV2
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ZXLD1366EV2
For low frequency, PWM capacitor C2 should be removed on the evaluation board, to give a more accurate duty
cycle.
Shorting R2 will connect the test pin ADJ to device pin ADJ if needed.
The external capacitor C2 on the ADJ pin sets the soft start time. The amount of soft start time achievable is
approximately 0.1ms/nF.
For other reference designs or further applications information, please refer to the ZXLD1366 datasheet.
Schematic Diagram
Figure 2 shows the schematic for the ZXLD1366EV2 evaluation board.
Vin
6
C1
ADJ
LED A
R1
4
Vin
C3
R2
3
C4
Isense
ZXLD1366DAC
ADJ
LX
D1
1
L1
LED K
C2
GND
2, 5
GND
Figure 2: Schematic for the evaluation board ZXLD1366EV2
ZXLD1366 Operation
In normal operation, when voltage is applied at +VIN, the ZXLD1366 internal NDMOS switch is turned on. Current
starts to flow through sense resistor R1, inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate
is determined by the input voltage +VIN and the inductor L1. This rising current produces a voltage ramp across R1.
The internal circuit of the ZXLD1366 senses the voltage across R1 and applies a proportional voltage to the input of
the internal comparator. When this voltage reaches an internally set upper threshold, the NDMOS switch is turned off.
The inductor current continues to flow through R1, L1, the LEDs, the Schottky diode D1, and back to the supply rail,
but it decays, with the rate of decay determined by the forward voltage drop of the LEDs and the Schottky diode. This
decaying current produces a falling voltage at R1, which is sensed by the ZXLD1366. A voltage proportional to the
sense voltage across R1 is applied at the input of the internal comparator. When this voltage falls to the internally set
lower threshold, the NDMOS switch is turned on again. This switch-on-and-off cycle continues to provide an average
current (set by the sense resistor R1) to the LEDs. Please refer to the datasheet for the threshold limits, ZXLD1366
internal circuits, electrical characteristics and parameters.
ZXLD1366EV2
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ZXLD1366EV2
ZXLD1366EV2 Evaluation Board - BOM
Ref
R1
R2
C1
C2,C3
C4
L1
Value
0.2R
1kΩ
10uF 100V
100nF, 100V
100nF 100V
150µH
Package
1210
0805
SMD
0805
1206
-
D1
U1
100V, 2A
ZXLD1366
SMB
DFN30306
Part Number
SR732ETTDR200F
Generic
NACEW100M1006.3x8TR13F
NMC0805X7R104K100TRPLPF
NMC1206X7R104K100TRPLP3KF
MSS1246-154ML
NPIS27H151LTRF
B2100
ZXLD1366DACTC
Manufacturer
KOA
NIC
NIC
NIC
Coilcraft
NIC
DIODES inc
Diodes Inc
Notes
1%, 100ppm
Electrolytic - 20%
20%
150µH
Schottky diode
DC-DC LED Driver
The Aluminium PCB design guarantees a good thermal dissipation for the ZXLD1366 device. Other sources of heat
are the Schottky diode, the inductor and the sense resistor. Care must be taken in their placement.
Warning: After 30 minutes of operation at 60V operation with 500mA output, the board temperature rises by
around 50°C above ambient.
Figure 3: Component layout and circuit board view
ZXLD1366EV2 Connection Point Definition
Name
Description
+VIN
Positive supply voltage.
GND
Supply Ground (0V).
ADJ
LED A
LED K
Internal voltage ref. pin (1.25V). This pin can be used to achieve dimming and soft-start,
and for switching the output current off.

Leave floating for normal operation.

See 'Circuit Features' section to achieve dimming, soft-start and for switching the
output current off.
LED A connects to the external LED anode
LED K connects to the external LED cathode
ZXLD1366EV2
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ZXLD1366EV2
ZXLD1366EV2 Basic operation at full voltage
1.
Connect external LEDs across test pins ‘LED A’ (anode) and ‘LED K’ (cathode). The number of external
LEDs that can be connected depends on their operating power and forward voltage drop, but typically 16 x
3.4V LEDs can be connected using a 60V rail. For an external load other than LEDs, the positive terminal of
the load should be connected the anode and the negative to the cathode.
2.
Connect VIN and GND.
Warning: The board does not feature reverse battery/supply protection.
3.
Set the PSU to the desired input voltage (usually between 30V and 60V)
4.
Turn on the PSU. The external LEDs will illuminate and the current should be approximately 1A
5.
LX waveforms can be acquired using the test point J1
Warning: Do not stare at the LEDs directly.
Circuit features
N.B. Remove power before changing components!
Soft-start
1.
The evaluation board is fitted with capacitor C2, which performs the soft start function by slowing the rise
time of the adjust pin at start-up. The pin output impedance is 50k so CxR is the time constant to reach 66%
of output current.
PWM
1.
Remove the soft start capacitor C2
2.
Refer to the datasheet for how to perform PWM
Switching off the output current
3.
Shorting the ADJ pin to GND will cause the LED current to go to zero. Releasing this pin will switch on the
system (creating a soft-start power up sequence if the C2 capacitor is used).
Changing the LED current
1.
Remove R1
2.
Calculate and fit a new sense resistor, R1, the value of which is based on the required LED current without
dimming. R1 can be calculated using following equation :
R1 = 0.2(V / IOUT) where
IOUT = the LED current.
R1 = the sense resistor value in ohms.
0.2V is the nominal sense voltage with ADJ open circuit or set to 1.25V.
PERFORMANCE
The system efficiency depends on the sense resistor, supply voltage, switching inductor, and the number of LEDs.
With a 60V supply and 15 LEDs, using and inductor of 150µH, the switching frequency is typically 100 kHz and
efficiency levels >94% are achievable.
Visit our website www.diodes.com to find useful tools for circuit design and simulation.
REFERENCE
[1] ZXLD1366 Datasheet – www.diodes.com
ZXLD1366EV2
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ZXLD1366EV2
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