ZXSC310EV6 User Guide Issue 1

ZXSC310EV6 EVALUATION BOARD USER GUIDE
ZXSC310 DESCRIPTION
The ZXSC310 is a single or multi-cell LED driver designed for LCD backlighting applications. The input voltage
range of the device is between 0.8V and 8V. This means that the ZXSC310 is compatible with single NiMH, NiCd
or Alkaline cells, as well as multi-cell or Li-Ion batteries.
The device features a shutdown control, resulting in a standby current less than 5µA, and an output capable of
driving serial or parallel LEDs. The circuit generates a constant power output, which is ideal for driving single or
multiple LEDs over a wide range of operating voltages. These features make the device ideal for driving LEDs in
LCD backlight applications, for example, in Digital Still cameras and PDAs.
The ZXSC310 is a PFM DC-DC controller IC that drives an external Zetex switching transistor with a very low
saturation resistance. Such transistors are excellent for this type of conversion, enabling high efficiency
conversion with low input voltages. The drive output of the ZXSC310 LED driver generates a dynamic drive
signal for the switching transistor.
The ZXSC310 is offered in the SOT23-5 package, which, when combined with a SOT23 switching transistor,
generates a high efficiency, small size circuit solution. The IC-and-discrete combination offers the ultimate costversus-performance solution for LED backlight applications.
FEATURES
TYPICAL APPLICATIONS
•
•
•
•
•
•
•
•
•
•
•
•
•
•
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94% efficiency
Minimum operating input voltage 0.8V
Maximum operating input voltage 8V
Standby current less than 5µA
Programmable output current
Series or parallel LED configuration
Low saturation voltage switching transistor
SOT23-5 package
LCD backlights:
Digital still camera
PDA
Mobile phone
LED flashlights and torches
White LED driving
Multiple LED driving
ORDERING INFORMATION
EVALBOARD ORDER NUMBER
ZXSC310EV6
DEVICE ORDER NUMBER
ZXSC310E5TA
Please note: Evaluation boards are subject to
availability and qualified sales leads.
Figure 1: ZXSC310EV6 evaluation board
Issue 1 – February 2009
© Diodes Incorporated, 2009
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ZXSC310EV6
REFERENCE DESIGN
Schematic Diagram
Vbatt
Vout
L1
10u
D1
ZHSC1000
U1
1
Vcc
3
Q1
ZXTN25012
5
Drive
En
Batt
2
GND
4
Sense
C2
1u
D2
K2
Vs
ZXSC310:
R6
20mR
Figure 2: Conceptual Schematic for the evaluation board ZXSC310EV6
(The LED is not fitted on the board)
The ZXSC310EV6, Figure 1, is an evaluation board for the ZXSC310 boost LED driver. It is
configured as in
Fig. 2, to drive approximately 200mA into either a single LED, or an external choice of LEDs, from a
single 1.5V battery.
The operating voltage is nominally 1.5 volts, but the circuit will operate from 0.8volts up to 8 volts. The
10uH inductor used in the circuit has been chosen as being the optimum value for this voltage range.
Power should be applied across the +VE and -VE pins, or, alternatively, a 1.5v ‘AA’ size battery can
be inserted in the clips provided. The nominal input current for the evaluation board is 600mA, and the
operating frequency will be about 250kHz
Note: The evaluation board does not have reverse battery protection.
WARNING: Exposed battery connections exist on the front and back of the board. Do not
cause the batteries to short-circuit by placing it on a conductive surface or allowing other
conductive materials to come into contact with it.
SL
2
3
P2
boost option
1
2
15u
1
2
SL
U1
P4
Bat1
Batt
D1
L1
1
TP
C1
1u
1
2
1
SL
3
2
Vcc
R1
R2
1
Vbatt
SL
Drive
5
3
10k@25C
En
GND
Q1
ZXTN25012EFH
Sense
4
SK1
C3
1u
2
TP3
P3
1
2
1
2
P1
D2
Rebel
R4
1
2
3
4
5
6
12
11
10
9
8
7
ZD1
BZX84-C10
100R
C2
1u
ZXSC310:
R5
20mR
FUTURE 6X2
TP4
TP
TP2
TP1
GND
The zener is to protect the transistor in case the led is not fitted.
Figure 3: Actual schematic for ZXSC310 EV6
(The LED is not fitted on the board)
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ZXSC310EV6
Differences between the Actual and Conceptual Schematics
The actual board has several different configurations, as in the schematic Fig. 3. Some of these are
not appropriate for this application.
R4 is not needed in this application, so a low (or zero) value resistor fitted.
For operation as described, solder links P1 and P4 should be shorted and P1 and P2 left open.
The LED is not fitted. A LED suitable for the actual application can be fitted on an external PCB via
SK1. The zener diode is fitted to protect Q1 against high voltages that would be produced by the
circuit of there was an open circuit load. It is not needed for applications where the LED is
permanently connected.
Design Procedure
The objective of this evaluation board is to drive the LED with the maximum current, subject to a
reasonable efficiency and component cost.
Fundamentally for this type of circuit the limiting factor is the peak current through the inductor. Using
the ZXTN25012 with the ZXSC310 at 1.0V to 1.5V the highest design current is about 1A. The
threshold Voltage on the Isense pin is given as 19mV so a 19mR resistor could be used. The next
highest preferred value is 20mR and the dissipation is only 20mW, so an 0805 package is adequate.
The ZXTN25012 is optimized for this type of application as it has an excellent combination of Vcesat
and gain at 1A. If a different type of transistor is used, the value of the sense resistor may have to be
increased, causing a reduction in output current.
The choice of inductor is a compromise between size and price. The small 10uH is a good
compromise here: a larger inductor value in the same case would have a higher series resistance and
hence higher losses. The value is not critical: a higher value could be used with little change in
performance. If the inductor is too small, not only is the power output reduced, but the circuit could
enter discontinuous mode, which is undesirable for e.m.c. and efficiency reasons.
The Schottky diode should have low forward voltage at 1A: the ZHSC1000 comes in a SOT23
package and has a Vf of about 400mV at 1A.
The output capacitor could be regarded as unnecessary, as the flicker that results from it’s omission is
not visible, but it helps with respect to e.m.c.
In this design the ‘Enable’ pin is tied to the Vcc pin (via solder link P4), as it’s functionality is not
used.
If no load is placed on the circuit, the output voltage continues to rise to an unacceptable level, so
ZD1 is included to limit the voltage to approximately 10volts.
For other reference designs or further applications information, please refer to the ZXSC310
datasheet, Application Notes and Design Notes at www.zetex.com.
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ZXSC310EV6
Figure 4: Component layout
ZXLD1360EV6 Component list
Designator
U1
ZD1
Q1
D1
Value
ZXSC310E5
BZX84C10 350mW
ZXTN25012EFH
ZHCS1000
Footprint
SOT23-5
SOT23A
SOT23
SOT23
C1, C2
1uF, 10V
0805
C3
1uF, 16V
0805
L1
R1
R2
R4
R5
SK1
SW1
Bat1
10uH 1.5A
10k
10k
100R
20mR
N/A
Slide switch, SPDT
Batt holder
NPIS73100
0805
0805
0805
0805
DIL
Name
+Ve
-Ve
TP1
TP2
LED+
LEDSK1
Part No
ZXSC310E5
ZXTN25012EFH
ZHCS1000
C0805C105K8RAC
GRM21BR71A105KA01L
NMC0805X7R105K10
C0805C105K4RAC
GRM21BR71C105KA01L
NMC0805X7R105K16
NPIS73T100MTRF
SMD 10k@25C 0805 NTC Thermistor
Resistor +/- 1%
Resistor +/- 1%
Resistor +/- 1%
Rapid 18-3505
Manufacturer
DIODES / ZETEX
DIODES / ZETEX
DIODES / ZETEX
DIODES / ZETEX
Kemet
Murata
NIC
Kemet
Murata
NIC
NIC
generic
generic
generic
generic
generic
generic
Keystone
Quantity
1
1
1
1
2
1
1
0
0
1
1
1
1
1
ZXLD1360EV6 Connection Point Definition
Description
Positive supply voltage.
Supply Ground (0V).
To monitor the voltage across the current sense resistor R6
Can be used to supply an Enable voltage if solder link P4 is opened.
External LED +ve
External LED -ve
The socket is designed to accept an LED Module Board. The pins are:
5 ,6, 7, 8 = LED cathode (-ve) and 1, 2, 11, 12 = LED anode (+ve).
Pins 3, 4, 9, and 10 are not used.
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ZXSC310EV6
ZXLD1360EV6 Basic operation at 1.5V
WARNING: Exposed battery connections exist on the front and back of the board. Do
not cause the batteries to short-circuit by placing it on a conductive surface or
allowing other conductive materials to come into contact with it.
1. Connect a power supply to TP3 (+ve) and TP4 (-ve) or insert an ‘AA’ size battery as depicted
on the top of the board .
Warning: The board does not have reverse battery/supply protection.
2. Set the PSU (if used), to 1.5V
3. Connect a suitable LED board to connector SK1, or an extyernal LED to LED+ and LED-. .
(The LED must be capable of handling 600mA)
4. Turn on the PSU (if used), and the switch SW1. The LED will illuminate and the current
should be approximately 600mA.
Warning: Do not look at the LED directly.
ZXSC310 Device Packages, Pin and Definitions
ZXSC310
Vcc
1
GND
2
En
3
5
Vdrive
4
Vsense
SOT23-5 package
ZXLD1360 Device Pin Definition
Name
Pin No
Description
VCC
1
Input Voltage
GND
2
Ground (0V).
Enable
3
Tie high for normal operation, low to shutdown
Vsense
4
From the sense resistor
Vdrive
5
Drive current output to transistor
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ZXSC310EV6
ZXSC310 Operation
The ZXSC310 is a constant off-time converter (also known as PFM). It operates as follows:On switch on, Q1 is switched on and the current through the inductor rises until the voltage across the
sense resistor R6 reaches the threshold (set by the device to about 20mV). Q1 is then switched off
for a constant time (determined by the internal device characteristics ) of about 1.5us. During this
time the inductor partially discharges into the load.
After the off-time, the cycle repeats.
It is worth noting that the frequency is determined by the ratio of the input voltage to the load voltage
(and the fixed off-time) and does not depend on the inductor value.
Test and Diagnostics
With this type of circuit the performance is best evaluated by watching the waveform on the current
sensing resistor. A test pad (TP1) has been provided for this purpose.
The voltage is normally 0-20mV so a sensitive oscilloscope with fairly narrow bandwidth is ideal.
This waveform with a corresponding inductor current waveform is shown schematically in Fig 5
188.8320u
196.7942u
I(L1-P) / mA
7.962140u
900
800
700
600
500
400
300
200
Inductor current
8.697934m
Vsense
U2-Vsense / mV
20
19.13537m
15
10.43743m
10
5
0
184
186
188
190
REF
192
194
196
198
200
A
Time/uSecs
2uSecs/div
Figure 5: Sample Waveforms
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ZXSC310EV6
Interpretation
The upper curve is the inductor current and this is not easy to measure without disturbing the circuit
operation.
The lower curve is the voltage across the sense resistor which actually contains more information, but
is less easy to interpret. This is the curve that can be seen from the test pad TP1.
The first thing to notice about this waveform is that the current starts from a non-zero value at the start
of the on period. This shows that the circuit is operating in continuous mode.
The current rise on the lower trace looks straight which shows that the inductor resistance is not very
high: if the resistances were high, the trace would sag towards the high current end and the circuit
efficiency would be poor.
The voltage in the off period is close to zero, which shows that the transistor Vcesat is not reducing
the efficiency significantly.
The ratio to on and off period is clearly defined showing that the circuit is operating cleanly. If the
waveforms were not well defined there would be a fault in the operation; possibly too low an input
Voltage
The maximum Voltage is about 20mV showing that the peak current is at the design level.
The minimum Voltage during the on period is about 10mV, so that the minimum current in this
example is 500mA, and hence the average input current in this example is 750mA .
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ZXSC310EV6
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.
Life support
Diodes Zetex 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.
Reproduction
The product specifications contained in this publication are issued to provide outline information only which (unless agreed by the company in
writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating
to the products or services concerned.
Terms and Conditions
All products are sold subjects to Diodes Inc. terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two
when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement.
For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes sales office.
Quality of product
Diodes Zetex Semiconductors Limited is an ISO 9001 and TS16949 certified semiconductor manufacturer.
To ensure quality of service and products we strongly advise the purchase of parts directly from Zetex Semiconductors or one of our regionally
authorized distributors. For a complete listing of authorized distributors please visit: www.zetex.com or www.diodes.com.
Diodes Zetex Semiconductors does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales
channels.
ESD (Electrostatic discharge)
Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The
possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent of damage
can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of
being affected should be replaced.
Green compliance
Diodes Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding
regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the
use of hazardous substances and/or emissions.
All Diodes Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with WEEE
and ELV directives.
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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