ZXSC380EV2 Datasheet and User Guide Issue 3

ZXSC380
Single or multi cell LED driver solution
Description
The ZXSC380 is a highly integrated single or
multi cell LED driver for applications where
step-up voltage conversion from a very low
input voltage is required. These applications
mainly operate from 1.5V or 1.2V cells. The IC
generates constant current pulses that are
ideal for driving single or multiple LEDs over
a wide range of operating voltages. The
ZXSC380 provides a simple to use, low cost,
space saving and easy to layout solutions.
The IC can start up under full load and operates
down to an input voltage of only 0.9V typical.
The ZXSC380 is offered in the space saving
SOT23 package or in die form, offering an
excellent cost vs performance solution for
single cell LED driving applications.
The ZXSC380 uses a PFM control technique to
drive an internal switching transistor which
has a low saturation resistance. This ensures
high efficiency, even for input voltages as low
as 1V.
SOT23
Features
Applications
•
80% efficiency
•
LED flashlights and torches
•
User adjustable output current
•
LED backlights
•
Single cell operation
•
White LED driver
•
Low saturation voltage switching transistor
•
Simple application circuit
•
Low external component count
•
SOT23 package
•
Available also in die form
Pin connections
Typical application circuit
VIN
L1
VCC 1
1
VCC
3 GND
ZXSC380
VOUT 2
GND
VOUT 2
3
LED1
Top view
GND
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ZXSC380
Absolute maximum ratings
Supply voltage (VCC)
-0.6V to 10V
Output voltage (VOUT)
-0.6V to 20V
Supply current
20mA
Output switch current
200mA
Power dissipation SOT23-3
450mW
Power dissipation die
1W
Operating temperature range
0°C to +85°C
Storage temperature range
-55°C to +150°C
Electrical characteristics
Measured at Tamb = 25°C, L = 100␮H and VCC = 1.5V unless otherwise specified.
Parameter
Conditions
Limits
Min.
Supply voltage operating range
Typ.
0.8
Minimum supply start-up voltage
Units
Max.
6
V
0.9
1.0
V
80
95
mA
0.5
V
Switch current
VOUT = 1.0V
Switch saturation voltage
IVOUT = 50mA
0.3
Mean LED current
VLED = 3.5V
18
mA
Efficiency
VLED = 3.5V
75
%
Operating frequency
VLED = 3.5V
160
kHz
65
Discharge pulse width
1.4
2.2
3.0
␮s
Pin descriptions
VCC 1
3 GND
VOUT 2
Top view
Pin descriptions
Pin No.
Name
Description
1
VCC
Supply voltage, generally Alkaline, NiMH or NiCd single cell
2
VOUT
Switch output external inductor/LED
3
GND
Ground
Ordering information
Device
ZXSC380FH
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Package
SOT23
Part Mark
380
2
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ZXSC380
Typical characteristics
Ivcc vs Supply Voltage for L = 100uH
80
100
70
90
80
60
70
Ivcc (mA)
LED Current, ILed (mA)
LED Current vs Supply Voltage for L = 100uH
50
40
30
60
50
40
30
20
20
10
10
0
0.5
1
1.5
2
2.5
0
3
0.5
Supply Voltage Vvcc (V)
1
1.5
2
2.5
3
Supply Voltage Vvcc (V)
Operating Waveforms
Efficiency vs Supply Voltgae for L = 100uH
100
90
Efficiency (%)
80
70
60
50
40
30
20
10
0
0.5
1
1.5
2
2.5
3
Supply Voltage Vvcc (V)
Channel 1 (lower): LED current ILed. 50mA/div.
Channel 2 (upper): Voltage at Vout pin. 1V/div
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ZXSC380
Typical characteristics
LED Current vs Supply Voltage
for L = 22, 47, 68 & 100uH
LED Current vs Supply Voltage
for L= 22, 47, 68 & 100uH
20
80
18
70
LED Current ILed (mA)
LED Current ILed (mA)
16
14
12
10
8
6
60
50
40
30
20
4
10
2
0
0
1
1.1
1.2
1.3
1.4
1
1.5
1.5
L = 100uH
L = 68uH
2
3
2.5
Supply Voltage Vvcc (V)
Supply Voltage Vvcc (V)
L = 47uH
L = 100uH
L = 22uH
Frequency vs Supply Voltage
for L= 22, 47, 68 & 100uH
L = 68uH
L = 47uH
L=22uH
Efficiency vs Supply Voltage
for L= 22, 47, 68 & 100uH
350
120
300
100
Efficiency (%)
Frequency (kHz)
250
200
150
80
60
40
100
20
50
0
0
1
1.5
2
2.5
3
1
Supply Voltage Vcc (V)
L = 100uH
L = 68uH
Issue 3 - September 2007
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L = 47uH
1.5
2
2.5
3
Supply Voltage Vvcc (V)
L = 22uH
L = 100uH
4
L = 68uH
L = 47uH
L = 22uH
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ZXSC380
Device description
The ZXSC380 is non-synchronous PFM, DC-DC controller IC which, with a high performance
internal transistor, for a high efficiency boost converter for use in single cell applications. A block
diagram is shown in Figure 1.
VCC
1
+
VREF
R1
2
VOUT
+
-
R2
I SENSE
R SENSE
3
GND
GND
Figure 1 ZXSC380 Block diagram
The on chip comparator forces the driver circuit and therefore the internal switching transistor to
switch off when the voltage at ISENSE exceeds 20mV. This threshold is set by an internal reference
circuit and divider. The voltage at ISENSE is taken from a current sense resistor connected in series
with the emitter of the switching transistor. This resistor is chosen to give 20mV at ISENSE for an
emitter current of 80mA.
A monostable following the output of the comparator forces the turn-off time of the output stage
to be typically 2.2␮s. This ensures that there is sufficient time to discharge a significant proportion
of the energy stored in the inductor coil before the next On period.
With every On pulse the switching transistor is kept on until the voltage across the current-sense
resistor exceeds the threshold of the ISENSE input. The On-pulse length, and therefore the
switching frequency, is determined by the programmed peak current, the input voltage and the
input to output voltage differential. See applications section for details.
The Driver circuit supplies the internal switching transistor with a fixed drive current. To maximize
efficiency the internal transistor is switched quickly, typically being switched off within 30ns.
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ZXSC380
Application notes
Typical application circuit
Figure 2 shows a typical boost circuit for 18mA LED current from a single cell 1.5V supply. The
inductor value is 100␮H. The operating frequency is typically 160kHz typical for 1.5V supply.
VIN
L1
100uH
1
VCC
ZXSC380
VOUT 2
GND
3
LED1
GND
Figure 2 Typical application circuit
The LED current can be set by the choice of inductor values described below.
Inductor selection and current setting
Figure 3 shows the LED current vs the supply voltage while Figure 4 shows the switching
frequency vs the supply voltage for various inductor values. Figure 3 and 4 can be used as guides
to the inductor value selection. The inductor should have a low DC resistance for high efficiency.
The switching frequency is dependent on the programmed peak current, the input voltage, the
input to output voltage differential and the inductor value.
LED Current vs Supply Voltage
for L = 22, 47, 68 & 100uH
20
18
LED Current ILed (mA)
16
14
12
10
8
6
4
2
0
1
1.1
1.2
1.3
1.4
1.5
Supply Voltage Vvcc (V)
L = 100uH
L = 68uH
L = 47uH
L = 22uH
Figure 3 The LED current vs the supply voltage for various inductor values
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ZXSC380
Frequency vs Supply Voltage
for L= 22, 47, 68 & 100uH
350
300
Frequency (kHz)
250
200
150
100
50
0
1
1.5
2
2.5
3
Supply Voltage Vcc (V)
L = 100uH
L = 68uH
L = 47uH
L = 22uH
Figure 4 Switching frequency vs the supply voltage for various inductor values
Bootstrap operation
The ZXSC380 can be operated in bootstrap mode, as shown in Figure 5, to operate down to 0.7V
typical after the initial successful start up. The operation down to 0.7V typical allows further cell
energy to be extracted beyond typically quoted end of battery voltage of approx. 0.9. This
prolongs the battery use time. (Note: Some batteries may have low voltage protections and may
switch the supply off.) The schotkky diodes, D1 and D2, should have a very low forward voltage,
e.g. of such part is Zetex ZHCS400 (SOD323 package) or Zetex BAT54C (dual schotkky diode with
common Cathode). The start up voltage is 0.9V typical without bootstrap, however, due to the
additional schotkky, D1, being in the path of the supply to the Vcc pin, the start up voltage can be
1.1V typical for the bootstrap configuration.
D2
L1
100uH
VIN
D1
1
VCC
C1
1uF
VOUT 2
GND
ZXSC380
3
LED1
GND
Figure 5 ZXSC380 in bootstrap mode
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ZXSC380
Intentionally left blank
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ZXSC380
Package outline - SOT23
E
e
e1
b
3 leads
L1
D
E1
A
A1
Dim.
L
c
Millimeters
Inches
Dim.
Millimeters
Min.
Max.
Min.
Max.
A
-
1.12
-
0.044
e1
A1
0.01
0.10
0.0004
0.004
E
2.10
2.64
0.083
0.104
b
0.30
0.50
0.012
0.020
E1
1.20
1.40
0.047
0.055
c
0.085
0.20
0.003
0.008
L
0.25
0.60
0.0098
0.0236
D
2.80
3.04
0.110
0.120
L1
0.45
0.62
0.018
0.024
-
-
-
-
-
e
0.95 NOM
Min.
0.037 NOM
Max.
Inches
1.90 NOM
Min.
Max.
0.075 NOM
Note: Controlling dimensions are in millimeters. Approximate dimensions are provided in inches
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ZXSC380
Definitions
Product change
Zetex Semiconductors 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 Zetex 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. Zetex 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
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 Zetex Semiconductors plc. 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
labelling 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
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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 Zetex sales office.
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Zetex 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/salesnetwork
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.
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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 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”
Future device intended for production at some point. Samples may be available
“Active”
Product status recommended for new designs
“Last time buy (LTB)”
Device will be discontinued and last time buy period and delivery is in effect
“Not recommended for new designs” Device is still in production to support existing designs and production
“Obsolete”
Production has been discontinued
Datasheet status key:
“Draft version”
This term denotes a very early datasheet version and contains highly provisional information, which
may change in any manner without notice.
“Provisional version”
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.
“Issue”
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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