ZXSC310
LED DRIVER SOLUTION FOR LCD BACKLIGHTING
DEVICE 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 the ZXSC310 is compatible with single
NiMH, NiCd or Alkaline cells, as well as multi-cell or
LiIon batteries.
The device features a shutdown control, resulting in a
standby current less than 5µA, and an output capable
of driving serial or parallel LED’s. The circuit generates
constant power output, which are ideal for driving
single or multiple LED’s over a wide range of operating
voltages. These features make the device ideal for
driving LED’s particularly in LCD backlight applications
for Digital Still cameras and PDA’s.
The ZXSC310 is a PFM DC-DC controller IC that drives
an external Zetex switching transistor with a very low
saturation resistance. These transistors are the best
switching devices available 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 circuit can start up under full load and operates
down to an input voltage of 0.8 volts. The solution
configuration ensures optimum efficiency over a wider
range of load currents; several circuit configurations
are possible depending on battery life versus
brightness considerations.
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
cost Vs performance solution for LED backlight
applications.
FEATURES
•
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
TYPICAL APPLICATIONS CIRCUIT
APPLICATIONS
•
LCD backlights:
Digital still camera
PDA
Mobile phone
•
LED flashlights and torches
•
White LED driving
•
Multiple LED driving
V
IN
= 3.3V / 5V
V
CC
V
DRIVE
S
TDN
I
SENSE
Gnd
ORDERING INFORMATION
DEVICE
REEL
SIZE
ZXSC310E5TA
180mm
TAPE
WIDTH
8mm
QUANTITY
PER REEL
3000
DEVICE MARKINGS
•
C310
Package SOT23-5
ISSUE 3 - SEPTEMBER 2007
1
SEMICONDUCTORS
ZXSC310
ABSOLUTE MAXIMUM RATINGS:
Supply Voltage
Maximum Voltage other pins
Power Dissipation
Operating Temperature
Storage Temperature
-0.3 to 10V
-0.3 to V
CC
+0.3V
450mW
-40 to 85 °C
-55 to 150°C
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: V
CC
=1.5V, T
AMB
=25 C
Symbol
Parameter
Efficiency
V
CC
V
CC(min)
(1)
Conditions
Min
Typ
Max
94
Units
%
V
V
Recommended supply
voltage range
Minimum startup and
operating voltage
Quiescent current
(2)
Base drive current
Supply current
(3)
I
DRIVE
=-600µA
,
V
DRIVE
=0.7V
I
DRIVE
=-600µA, V
DRIVE
=0.7V,
T
AMB
=-10°C
(3)
V
EN =
V
CC
(enabled)
V
EN =
0V (standby)
V
DRIVE
= 0.7V, V
ISENSE
= 0V
V
DRIVE
= 0.7V, V
ISENSE
= 0V
V
ISENSE
= 0V, I
VDRIVE
=-0.5mA
V
ISENSE
= 50mV, I
VDRIVE
= 5mA
0.8
0.8
0.9
0.2
5
1.5
2
8
0.92
I
Q
I
VDRIVE
I
CC
V
VDRIVE(high)
V
VDRIVE(low)
V
STDN(high)
V
STDN(low)
I
STDN
V
ISENSE
(threshold)
mA
10
3.5
4
µA
mA
mA
High level drive voltage
Low level drive voltage
Device enabled
Device in standby mode
Enable input current
Output current reference
voltage
I
SENSE
voltage temp co.
(2)
I
SENSE
input current
Discharge Pulse Width
V
CC
-0.3
0
0.7
V
CC
0.2
V
V
V
0.15
-1
14
19
0.4
V
ISENSE
= 0V
0
1.2
-30
1.7
-65
3.2
1
24
V
µA
mV
%/°C
µA
µs
T
CVISENSE
I
ISENSE
T
DRV
OPERATING CONDITIONS
Symbol
F
OSC
Parameter
Recommended operating
frequency
(4)
Conditions
Min
Typ
Max
200
Units
kHz
(1) Application dependent, see reference designs
(2) These parameters guaranteed by Design and characteristics
(3) Total supply current =I
Q
+ I
VDRIVE
, see typical characteristics
(4) Operating frequency is application circuit dependent. See applications section.
ISSUE 3 - SEPTEMBER 2007
SEMICONDUCTORS
2
ZXSC310
FMMT618
For the circuits described in the applications section
Zetex FMMT618 is the recommended pass transistor.
The following indicates outline data for the device,
m ore detailed i nform a tion can be found at
www.zetex.com/fmmt618
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: T
AMB
=25 C
Symbol
V
CE(sat)
Parameter
Collector-Emitter
Saturation Voltage
5
Conditions
I
C
=0.1A, I
B
=10mA
I
C
=1A, I
B
=10mA
I
C
=2.5A, I
B
=50mA
V
(BR)CEO
5
Min
Typ
8
70
130
Max
15
150
200
Units
mV
Collector-Emitter
Breakdown Voltage
5
I
C
=10mA
20
27
V
Measured under pulse conditions. Pulse width=300µs. Duty cycle
2%
ZHCS1000
For the maximum brightness circuit described in the
applications section Zetex ZHCS1000 is the
recommended Schottky diode.
The following indicates outline data for the ZHCS, more
detailed i nform a tion can be found at
www.zetex.com/zhcs1000
ELECTRICAL CHARACTERISTICS:
Test conditions unless otherwise stated: T
AMB
=25 C
Symbol
V
F
t
rr
Parameter
Forward voltage
Reverse Recovery Time
Conditions
I
F
= 500mA
I
F
= 1A
Switched from I
F
=500mA to
I
R
=500mA.
Measured at I
R
=50mA
I
R
Reverse Current
V
R
= 30V
50
100
µA
12
Min
Typ
Max
400
500
ns
Units
mV
Part
Number
V
R
Max.
V
I
F
Max.
mA
200
2000
1000
750
500
400
I
FSM
Max.
A
0.6
20
12
12
6.75
6.75
V
F
at
Max.
mV
500
500
500
540
550
500
I
F
mA
30
2000
1000
750
500
400
I
R
at
Max.
A
250
1000
100
100
40
40
V
R
V
25
30
30
30
30
30
Capacitance
at V
R
= 25V, f = 1MHz
Typ.
pF
10
60
25
25
20
20
Package
SOT23
SOT23-6
SOT23
SOT23
SOT23
SOT23
SOT323
BAT54
ZHCS2000
ZHCS1000
ZHCS750
ZHCS500
ZHCS400
30
40
40
40
40
40
ISSUE 3 - SEPTEMBER 2007
3
SEMICONDUCTORS
ZXSC310
TYPICAL CHARACTERISTICS
ISSUE 3 - SEPTEMBER 2007
SEMICONDUCTORS
4
ZXSC310
DEVICE DESCRIPTION
The ZXSC310 is PFM, controller IC which, when
combined with a high performance external transistor,
enables the production of a high efficiency boost
converter for LED driving applications. A block diagram
is shown for the ZXSC310 below.
The on chip comparator forces the driver circuit and
therefore the external switching transistor off if the
voltage at I
SENSE
exceeds 19mV. An internal reference
circuit and divider set this threshold.
The voltage at I
SENSE
is taken from a current sense
resistor connected in series with the emitter of the
switching transistor. A monostable following the
output of the comparator forces the turn-off time of the
output stage to be typically 1.7us. This ensures that
there is sufficient time to discharge 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 I
SENSE
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 external switching
transistor with a fixed drive current. To maximise
efficiency the external transistor switched quickly,
typically being forced off within 30ns.
V
CC
I
2
S
TDN
Drive
R1
V
RE
I
R2
V
DRIVE
I
SENSE
G
ND
ZXSC310 Block Diagram
ISSUE 3 - SEPTEMBER 2007
5
SEMICONDUCTORS
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