ZXLD383

A Product Line of
Diodes Incorporated
ZXLD383
SINGLE OR MULTI CELL LED DRIVER SOLUTION
Summary
The ZXLD383 is a single or multi cell LED driver designed for applications requiring step-up voltage conversion from a very
low input voltage. The IC generates constant current pulses that are ideal for driving single or multiple LEDs over a wide
range of operating voltages. It includes an on/off enable input that can be driven directly from a photocell array or an open
collector/drain logic output. The enable input features an ultra-low voltage drop diode to ground, eliminating the need for a
photocell array isolation diode in Garden Light applications.
The ZXLD383 uses a PFM control technique to drive an internal switching transistor which exhibits a low saturation
resistance. This ensures high efficiency, even for input voltages as low as 1.0V.
The IC can start up under full load and operates down to an input voltage of below 0.9V.
The ZXLD383 is offered in the space saving TSOT23-5 package or in die form, offering an excellent cost vs. performance
solution for single cell LED driving applications.
Features
•
•
•
•
•
•
•
Pin Assignments
85% Efficiency
User adjustable output current
Single cell operation
Low saturation voltage
TSOT23-3 package
Available also in die form
Simple application circuit
TSOT23-3
ENA 1
VCC
4
VOUT
GND 2
NC 3
(Top View)
Application
•
•
•
•
•
•
5
Garden lights
Door/pathway illumination
LED flashlight and torches
LED backlights
White LED driver
Gated boost supply generator
Typical Application Circuit
ZXLD383
Document number: DS32189 Rev. 3 - 2
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ZXLD383
Block Diagram
VC C
L1
Z XLD 383
D iode Array
VO U T
EN A
Puls e
C ontrol
N IMH
1.2V
LED
Dch
C on
Coff
R s ens e
GN D
Fig 1. ZXLD383 Block Diagram
Pin Description
Pin No.
1
2
3
Name
ENA
GND
NC
Description
Enable / Photodiode array battery charge input
Ground
Not connected (internally open circuit)
4
VOUT
Switch output external inductor/LED
5
VCC
Supply voltage, generally Alkaline, NiMH or NiCd single cell
ZXLD383
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ZXLD383
Absolute Maximum Ratings
Rating
Unit
Supply Voltage (VCC)
Parameter
-0.6 to 6
V
Output Voltage (VOUT)
-0.6 to 20
V
Enable Voltage (VENA)
Supply Current
Output Switch Current
Power Dissipation (TSOT23-3)
Power Dissipation Die
Operating Temperature Range
Storage Temperature Range
-1 to 3.5
V
20
800
450
1
-20 to 85
-55 to 150
mA
mA
mW
W
°C
°C
Electrical Characteristics
Measured at TAMB = 25°C, L = 6.8µH, IENA = 0 and VCC = 1.5V unless otherwise specified.
Parameter
Conditions
Supply Voltage Operating Range
Minimum Supply Start-up Voltage
Supply Current Quiescent
L = 10μH
L = 10μH
Supply Current Shutdown
VENA = VCC – 0.8V
Supply Current Under-Voltage
VCC = 0.6V
Switch Current
At turn-off
Min
0.9
2
250
Switch Saturation Voltage
IOUT = 200mA
Switch Leakage Current
VOUT = 20V, VENA = 0V
Mean LED Current
VLED = 3.5V
Efficiency
VLED = 3.5V
Operating Frequency
VLED = 3.5V
40
Limits
Typ.
Units
0.8
4
Max
3.3
0.9
8
17
30
µA
20
µA
V
V
mA
320
400
mA
100
300
mV
10
µA
65
mA
50
85
%
330
kHz
Discharge Pulse Width
0.7
1.5
2.5
µs
Enable Input Threshold
VCC - 0.6
-11
VCC - 0.2
-20
µA
-90
-250
mV
Enable Input Current
VENA = 0.2V
VCC - 0.8
0
Enable Input Voltage
IENA = -20mA
0
ZXLD383
Document number: DS32189 Rev. 3 - 2
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ZXLD383
Device Description
The ZXLD383 is a simple PFM, DC-DC controller combined with a high performance internal switching transistor, enabling
the production of a high efficiency boost converter for use in single cell applications. It includes a dual function Enable input
which serves both as an operation inhibit control and an ultra-low voltage drop isolation diode for battery charging purposes
in Garden Light applications. A block diagram is shown for the ZXLD383 in Figure 1.
With power applied and the enable pin held at VCC, an oscillator within the pulse control block forces the internal switching
transistor to switch on to start an energy charge cycle. The low saturation voltage switch pulls the VOUT pin close to ground
which forces the supply voltage across the external inductor L1. This causes a current to build up, storing energy in the
inductor. During this phase, switch current and supply voltage are monitored and used by the pulse control circuit to
determine the optimum drive conditions and on-time. At the end of the energy charge cycle, the internal switch is turned off
rapidly, interrupting the current flow through L1 which causes the voltage on VOUT to rise dramatically. When the voltage on
VOUT reaches the load LED’s forward (on) voltage, the inductor current is transferred from the internal switch to the LED,
starting the energy discharge cycle. With the voltage across the inductor reversed, the current flowing through it (and the
LED) now falls. When the inductor current reaches zero, the voltage on the VOUT pin falls back towards VCC. This action is
sensed by the pulse control circuit and is combined with the output of an off-period timer to initiate the next energy charge
cycle. Except for low level losses, all the energy stored in the inductor during a charge cycle is channeled to the load LED
during the following discharge cycle.
The current fed into the load LED has a sawtooth waveform, the average (DC) value of which is kept constant by the pulse
control circuit for varying supply voltage and temperature. It is possible to change the output current given by the ZXLD383
by changing the value of inductor L1. The larger the inductance of L1, the lower the output current. A table/graph showing
the relationship between inductance and output current is given later in this datasheet. Since the output current of the
ZXLD383 is a sawtooth waveform, its peak value is substantially larger than the DC/average value. The table also provides
this data.
The internal switching transistor has a minimum collector-emitter breakdown voltage of 20V and this sets the maximum
load voltage allowable. The minimum value is set by a feature of the pulse control circuit that requires the load voltage to
be at least 0.5V greater than VCC. (The device will function with load voltages smaller than this but output current regulation
will be impaired.) Higher than nominal load voltages will lower the average (DC) output current generated for a given
inductor value.
The Enable pin inhibits the operation of the output switch if held at a potential of Vcc-0.8V or lower. It also includes a diode
to ground which allows the input to be wired directly to a photocell array that will then both enable operation of the
converter when in darkness and charge the IC’s power source in daylight conditions. The diode function is performed by an
active circuit that gives an ultra low forward voltage drop (typically less than 0.1V at 20mA). This allows the use of a lower
output voltage photocell array (lower cost) without degrading performance.
ZXLD383
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ZXLD383
Typical Characteristics
90
100
22µH
10µH
80
90
4.7µH
80
70
6.8µH
70
Efficiency (%)
IOUT (mA)
60
50
10µH
40
60
50
40
6.8µH
30
30
22µH
20
20
4.7µH
47µH
10
0
47µH
10
0.8
1
1.2
1.4
1.6
V CC (V)
IO UT(AVERAG E) vs. V CC
1.8
0
2
0.8
1
1.2
1.4
1.6
1.8
V CC (V)
Efficiency vs. V CC for L = 2.2µH to 47µH
2
500
250
450
350
4.7µH
6.8µH
150
IIN (mA)
IIN (mA)
4.7µH
400
200
6.8µH
300
250
10µH
200
100
10µH
150
22µH
50
22µH
100
47µH
50
47µH
0
0.8
Notes:
0
1
1.2
1.4
1.6
V CC (V)
I IN vs. VC C
1.8
2
0.8
1
1.2
1.4
1.6
V CC (V)
Peak IIN vs. VCC
1.8
2
VLED = 3.5V for all graphs
ZXLD383
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ZXLD383
Typical Characteristics (Cont.)
450
400
0.8V
350
V ENA (mA)
300
1.0V
250
1.2V
200
150
100
50
1.4V
0
0
Notes:
10
20
30
40
IV ENA (mA)
V(ENA) vs. IENA
For VI N = 0.8, 1.2, 1.4V
50
Channel-1 (Upper): I LED @ 100mA/cm
Channel-2 (Lower): VO UT @ 1V/cm
Timebase: 500ns/cm
Operating Waveform for L = 6.8µH, V CC = 1.5V
VLED = 3.5V for all graphs
ZXLD383
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ZXLD383
Application Examples
Apart from the Garden Light application circuit shown on the front page of this datasheet, the ZXLD383 may be used in
many other ways. The following circuits and notes show some other possibilities and give typical performance details.
Standard operating mode
The following circuit demonstrates how few components are required to produce a light source using the ZXLD383.
Operating from a single cell, this simple circuit is suited for use in car key fobs, novelty products etc. where small size and
low cost are critical aspects.
By directly wiring the ENA pin to VCC, the part is permanently enabled once a power supply is provided. The ZXLD383 is
highly tolerant of supply ripple so no decoupling of VCC should be needed in a compactly constructed circuit. Also, the
part’s capability of operating with a VCC below 0.9V means that this simple circuit will make the best use of available battery
capacity.
The attached table shows the average LED currents that can be obtained using a range of inductor values. Also shown are
the peak currents required to achieve the given currents.
Z XLD 383
EN A
GN D
NC
5
1
VC C
I L E D (peak )
I L E D (avg)
(uH )
(m A )
(m A )
L1
2
4
3
VOU T
1.5V
LED
Notes:
L
47
45
8.5
22
100
17.3
10
210
34
6.8
330
50
4.7
415
63
VLED = 3.5V
Low Ripple LED Current Mode
It is possible that the peak LED current required to achieve a given average current is either too high for the LED of choice
or it leads to some loss of efficiency (due to LED resistance losses). In these cases, just two extra low cost components
can be added to provide a low ripple current supply for the LED. The Schottky diode D1 and capacitor C1 rectifies and
smoothes the output of the ZXLD383 giving a low ripple current supply to the load LED. Of course, this circuit could also be
used to power loads other than LEDs.
Z XL D 3 8 3
EN A
GN D
1
5
VC C
L1
2
D1
NC
3
4
VOU T
C1
1.5V
LED
L
IL E D
(uH )
(m A )
47
7.5
22
15.5
10
31
6.8
46
4.7
58
Notes: VLED = 3.5V, D1 = ZHCS1000, C1 = 1µF (low ESR)
ZXLD383
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ZXLD383
Buck-boost mode
Simple boost converters can run into problems when the input supply voltage is similar to or exceeds the intended load
voltage as there is usually a direct current path from the power source through to the load via the boost inductor. This path
does not require switching action and so is uncontrolled. When using the ZXLD383, this problem can be avoided by wiring
the cathode of the load LED to Vcc rather than ground. Without switching action, the LED is reverse-biased and so no
current can flow. When switching, the anode of the LED is driven to Vcc + Vf(led). The higher than normal output voltage
reduces the available output current as described earlier and this is shown in the typical data provided.
LED
Z XLD 383
3V
EN A
1
GN D
5
VC C
L1
2
NC
4
3
L
IL E D
(uH )
(m A )
47
5.5
22
10.3
10
23.2
6.8
36.7
4.7
46.2
VO U T
Notes: VLED = 3.5V
Low ripple buck-boost mode
The output of the Buck-Boost converter can be rectified and smoothed as with the standard circuit to give a low ripple
output to improve LED efficiency or to give a DC output for other loads.
C1
LED
Z XLD 383
3V
EN A
GN D
1
5
VC C
L1
2
L
IL E D
(uH )
(m A )
47
5
22
9 .7
10
2 1.7
6.8
34
4.7
43
D1
NC
3
4
VO U T
Note: VLED =3.5V, D1=ZHCS1000, C1 = 1uF (low ESR)
ZXLD383
Document number: DS32189 Rev. 3 - 2
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ZXLD383
Ordering Information
Part Number
Package
Part Mark
ZXLD383ET5TA
TSOT23-5
383
Tape Width
(mm)
8
Quantity
(per reel)
3000
Package Outline Dimensions
Millimeters
Inches
Dim.
Millimeters
Inches
Dim.
Min.
Max.
Min.
Max.
A
-
1.00
-
0.0393
E1
1.60 BSC
0.062 BSC
A1
0.01
0.10
0.0003
0.0039
e
0.95 BSC
0.037 BSC
A2
0.84
0.90
0.0330
0.0354
1.90 BSC
0.074 BSC
b
0.30
0.45
0.0118
0.0177
L
C
0.12
0.20
0.0047
0.0078
L2
D
2.90 BSC
0.114 BSC
E
2.80 BSC
0.110 BSC
ZXLD383
Document number: DS32189 Rev. 3 - 2
Min.
0.10
Q
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Max.
0.60
0.25 BSC
4
12
Min.
0.0039
Max.
0.0236
0.010 BSC
4
12
May 2010
© Diodes Incorporated
A Product Line of
Diodes Incorporated
ZXLD383
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ZXLD383
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