ZXLD1356EV1 User Guide Issue 1

ZXLD1356EV1 USER GUIDE
DESCRIPTION
The ZXLD1356EV1, Figure 1, is a PCB constructed using an FR4 base for evaluating the ZXLD1356 LED driver
with internal switch in SOT23-5 package. 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. [1]
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 550mA with a 0.36Ω sense resistor, R1//R3.
The 150uH 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 550mA output, the connected LED will be hot and very bright
Figure 1: ZXLD1356EV1 evaluation board
ZXLD1356 DEVICE DESCRIPTION
The ZXLD1356 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 550mA.
ZXLD1356 DEVICE FEATURES
•
Typical accuracy better than 0.8%
•
Enhanced thermal capability in DFN633 package
•
Drives one or more series-connected LEDs
•
LEDs up to 550mA.
•
Internal 60V switch.
•
Wide input voltage: 7V to 60V.
•
Inherent open circuit LED protection.
•
Brightness control using DC or PWM.
•
Internal PWM filter.
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DEVICE APPLICATIONS
•
LED flashlights.
•
High Power LED driving.
•
Low-voltage halogen replacement LEDs.
•
Automotive lighting.
•
Illuminated signs.
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ZXLD1356EV1
ZXLD1356 Device Packages, Pin and Definitions
TSOT23-5 and DFN633 package options
ZXLD1356 Device Pin Definition
Name
Pin No
LX
1
GND
2
ADJ
3
ISENSE
4
VIN
5
Description
Drain of NDMOS switch.
Ground (0V).
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.
Connect a sense resistor, Rs= R1//R3, from the ADJ pin to VIN to sense the
nominal output current. Nominal Iout = 0.2/ Rs
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
ZXLD1356EV1
DEVICE ORDER NUMBER
ZXLD1356DAC
ZXLD1356E5TA
Please note: Evaluation boards are subject to
availability and qualified leads.
ZXLD1356EV1 EVALUATION BOARD
REFERENCE DESIGN
The ZXLD1356EV1 is an evaluation board configured to be used with the ZXLD1356 in SOT23-5 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 550mA with a 0.36Ω sense resistor R1.
The device operates in continuous mode at approximately 120 kHz, with a 150uH 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
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ZXLD1356EV1
filter and the voltage across the capacitor represents a more stable dc reading of current. Using this method,
200mV represents 0.55 Amp when using a 0.36Ω sense resistor.
The ADJ pin connects to a low pass filter within the ZXLD1356 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.
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 ZXLD1356 datasheet.
Schematic Diagram
Figure 2 shows the schematic for the ZXLD1356EV1 evaluation board.
LED A
R1//R3
Vin
5
4
C4
Vin
V sense
D1
C3
C1
L1
ADJ
R2
3
ADJ
ZXLD1356
1
LX
LED K
C2
GND
GND
Figure 2: Schematic for the evaluation board ZXLD1356EV1
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ZXLD1356EV1
ZXLD1356 Operation
In normal operation, when voltage is applied at +VIN, the ZXLD1356 internal NDMOS switch is turned on.
Current starts to flow through sense resistor R1//R3, 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//R3. The internal circuit of the ZXLD1356 senses the voltage across R1//R3 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//R3, 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//R3,
which is sensed by the ZXLD1356. A voltage proportional to the sense voltage across R1//R3 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 resistors
R1 and R3) to the LEDs. Please refer to the datasheet for the threshold limits, ZXLD1356 internal circuits,
electrical characteristics and parameters.
ZXLD1356EV1 Evaluation Board - BOM
Ref
R1
R2
R3
C1
C2,C4
C3
L1
D1
U1
Value
0.36R
1kΩ
Package
1206
0805
10uF 100V
100nF, 100V
100nF
150uH
100V, 2A
ZXLD1356
SMD
0805
1206
SMB
TSOT23-5
Part Number
SR732BTTDR360F
Generic
Not fitted
NACEW100M1006.3x8TR13F
NMC0805X7R104K100TRPLPF
NMC1206X7R104K100TRPLP3KF
NPIS104F151MTRF
B2100
ZXLD1356E5TA
Manufacturer
KOA
-
Notes
1%, 100ppm
-
NIC
NIC
NIC
NIC
DIODES inc
Zetex
Electrolytic - 20%
20%
150uH
Schottky diode
DC-DC converter
The FR4 PCB design guarantees a good thermal dissipation for the ZXLD1356 device. Other sources of heat are
the Schottky diode, the inductor and the sense resistor. Care must be taken in their placement.
Warning: At 60V operation with 500mA output, the board temperature rises by around 50C from ambient
after 30 minutes of operation.
Figure 3: Component layout and circuit board view
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ZXLD1356EV1
ZXLD1356EV1 Connection Point Definition
Name
Description
+VIN
Positive supply voltage.
GND
Supply Ground (0V).
ADJ
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
LED A
LED K
ZXLD1356EV1 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 500mA
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 whilst 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 and R3
2.
Calculate and fit a new sense resistor, R1//R3, the value of which is based on the required LED current
without dimming. R1//R3 can be calculated using following equation :
R1//R3 = 0.2(V / IOUT)
where IOUT = the LED current.
R1,R3 = the sense resistors value in ohms.
0.2V is the nominal sense voltage with ADJ open circuit or set to 1.25V.
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ZXLD1356EV1
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, the switching frequency is typically 200 kHz and efficiency levels >90% are
achievable.
Visit our website www.zetex.com to find useful tools for circuit design and simulation.
REFERENCE
[1] ZXLD1356 Datasheet – www.zetex.com
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ZXLD1356EV1
INTENTIONALLY BLANK
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ZXLD1356EV1
Definitions
Product change
Diodes Incorporated reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service.
Customers are solely responsible for obtaining the latest relevant information before placing orders.
Applications disclaimer
The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the
user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by
Diodes Inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from
such use or otherwise. Diodes Inc. does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including
negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential
loss in the use of these circuit applications, under any circumstances.
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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.
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For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes sales office.
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To ensure quality of service and products we strongly advise the purchase of parts directly from Zetex Semiconductors or one of our regionally
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Diodes Zetex Semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales
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Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The
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can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of
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Product status key:
“Preview”
“Active”
“Last time buy (LTB)”
“Not recommended for new designs”
“Obsolete”
Datasheet status key:
“Draft version”
“Provisional version”
“Issue”
Future device intended for production at some point. Samples may be available
Product status recommended for new designs
Device will be discontinued and last time buy period and delivery is in effect
Device is still in production to support existing designs and production
Production has been discontinued
This term denotes a very early datasheet version and contains highly provisional
information, which may change in any manner without notice.
This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance.
However, changes to the test conditions and specifications may occur, at any time and without notice.
This term denotes an issued datasheet containing finalized specifications. However, changes to
specifications may occur, at any time and without notice.
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