DIODES ZXLD1100

ZXLD1100
ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH AND OPEN
CIRCUIT PROTECTION IN SC70-6
DESCRIPTION
The ZXLD1100 is a PFM inductive boost converter
designed for driving 2, 3 or 4 series connected white
LEDs from a Li-Ion cell and up to 8 LEDs from a 5V
supply. The device operates from an input supply of
between 2.5V and 5.5V and provides an adjustable
output current of up to 50mA.
The ZXLD1100 includes the output switch and peak
current sense resistor, and can operate with a
maximum output voltage of 28V.
Output current can be adjusted by applying a PWM
control signal to the 'Enable' pin. Depending upon the
control frequency, this will provide either a continuous
or a 'chopped' output current. The PWM filter
components are contained within the chip.
Quiescent current is typically 60␮A and a shutdown
function is provided to reduce this current to less than
500nA in the 'off' state.
The device is assembled in a low profile SC70-6 pin
package with industry standard pinout.
ADVANCED FEATURES
APPLICATIONS
• Internal 30V NDMOS switch, current sense and
• Mobile phones
The ZXLD1100 contains an internal avalanche diode to
protect the output switch. This allows the device to
operate indefinitely if the load is open circuit. Input
supply current during this condition is less than 1mA.
open circuit protection
• True Analog Dimming via PWM
• Digital cameras
FEATURES
• PDAs
•
•
•
•
•
•
•
•
•
•
• LCD modules
Low profile SC70 6 pin package
Internal PWM filter for flicker free output
High efficiency (80% typ)
Wide input voltage range: 2.5V to 5.5V
Up to 50mA output current
Low quiescent current: (60␮A typ)
500nA maximum shutdown current
Up to 1MHz switching frequency
Low external component count
Inherently matched LED currents
• Portable internet appliances
• Palmtop computers
TYPICAL APPLICATION CIRCUIT
PIN CONNECTIONS
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1
SEMICONDUCTORS
ZXLD1100
ORDERING INFORMATION
DEVICE
ZXLD1100H6
DEVICE DESCRIPTION
TEMPERATURE RANGE
PART MARK
TAPING
OPTIONS
Boost convertor in SC70-6
-40 to +85°C
110
TA, TC
ZXLD1100H6TA = 7” reel of 3,000 devices
ZXLD1100H6TC = 13” reel of 10,000 devices
ABSOLUTE MAXIMUM RATINGS (Voltages to GND unless otherwise stated)
PARAMETER
SYMBOL
LIMIT
UNIT
Input voltage
(V IN )
7
V
LX output voltage
(V LX )
30
V
Switch output current
(I LX )
500
mA
Power dissipation
(PD)
300
mW
Operating temperature
(T OP )
-40 to 85
°C
Storage temperature
(T ST )
-55 to 150
°C
Junction temperature
(T j MAX )
125
°C
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SEMICONDUCTORS
2
ZXLD1100
ELECTRICAL CHARACTERISTICS (at VIN = 3V, Tamb = 25°C unless otherwise stated(1))
SYMBOL
PARAMETER
V IN
Input voltage
I IN
Supply current
CONDITIONS
MIN.
TYP.
2.5
Quiescent
V EN = V IN , I LX = 0,
Output not switching
Shutdown
V EN = 0V
V FB
FB pin control voltage
I FB
FB pin input current
f LX
Operating frequency
60
90.5
L=10␮H, V OUT =10V,
I OUT =20mA
0.35
350
MAX. UNIT
5.5
V
100
␮A
500
nA
109.5
mV
100
nA
1
MHz
5
µs
T OFF
LX output 'OFF' time
T ON
LX output 'ON' time (2)
I LXpk
Switch peak current limit
R LX
Switch 'On' resistance
I LX(leak)
Switch leakage current
V LX =20V
1
µA
V OUT
Controller output voltage
Normal operation
VSENSE pin
open-circuit or
grounded
28
V
L=10␮H, V OUT =10V,
I OUT =20mA
25
1.5
V ENH
EN pin High level Input voltage
Device active
EN pin Low level Input voltage
Device in shutdown
I ENL
EN pin Low level input current
V EN =0V
I ENH
EN pin High level input current
V EN =V IN
V EN switched from
high to low
(4)
∆T/T
PWM duty cycle range at ‘EN’ input for
filtered PWM control (5)
f LPF
Internal PWM low pass filter cut-off
frequency
A LPF
Filter attenuation
320
VSENSE connected to
Vout
V ENL
EN pin turn off delay
ns
mA
⍀
1.5
V OUT(MAX) Controller output voltage with output
open circuit (3)
T EN(hold)
500
10kHz < f < 100kHz,
V ENH =V IN
f=30kHz
30
V
VIN
V
-100
nA
1
␮A
120
20
V
0.4
µs
100
%
4
kHz
52.5
dB
NOTES:
(1) Production testing of the device is performed at 25°C. Functional operation of the device over a -40°C to +85°C temperature range is
guaranteed by design, characterization and process control.
(2) Nominal 'on' time (TONnom) is defined by the input voltage (VIN), coil inductance (L) and peak current (ILXpkdc) according to the expression:
TONnom = {ILX(pkdc) x L/VIN} +200ns.
(3) When using the open circuit protection feature, the maximum output voltage under normal operation should be maintained below the
minimum value specified, in order to prevent possible disturbance of the current control loop.
(4) This is the time for which the device remains active after the EN pin has been asserted low. This delay is necessary to allow the output to be
maintained during dc PWM mode operation.
(5) The minimum PWM signal frequency during this mode of operation is to ensure that the device remains active during PWM control. This
provides a continuous dc output current. For lower frequencies, the device will be gated 'on' and 'off' during PWM control.
(6) The maximum PWM signal frequency during this mode of operation should be kept as low as possible to minimize errors due to the turn-off
delay of the device (see Enable pin turn-off delay).
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SEMICONDUCTORS
ZXLD1100
PIN DESCRIPTION
PIN NO.
NAME
DESCRIPTION
1
LX
Output of NDMOS switch
2
GND
Ground (0V)
3
FB
Feedback pin for current control loop (connect resistor R1
from this pin to GND for output current I=100mV/ R1)
4
EN
Enable input (active high to turn on device)
Also used to adjust output current by PWM signal.
Connect to V in for permanent operation.
5
VSENSE
Output voltage sense (used for open circuit protection).
Connect to GND if not required.
6
V IN
Input voltage (2.5V to 5.5V). Decouple with capacitor close
to device.
BLOCK DIAGRAM
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ZXLD1100
DEVICE DESCRIPTION
The device is a PFM flyback dc-dc boost converter,
working in discontinuous mode.
Filtered PWM operation
The input of an internal low pass filter is switched to
VREF when the EN pin is high and switched to ground
when the EN pin is low. The output of this filter drives
the comparator within the control loop. A continuous
high state on EN therefore provides a filtered voltage of
value VREF to the comparator. However, by varying the
duty cycle of the EN signal at a suitably high frequency
(f>10kHz), the control loop will see a voltage, that has
an average value equal to the duty cycle multiplied by
VREF. This provides a means of adjusting the output
current to a lower value. It also allows the device to be
both turned on and adjusted with a single signal at the
'EN' pin. The output during this mode of operation will
be a dc current equal to (VREF/R1) x duty cycle
With reference to the chip block diagram and typical
application circuit, the operation of the device is as
follows:
Control loop
When 'EN' is high, the control circuits become active
and the low side of the coil (L1) is switched to ground
via NDMOS transistor (MN). The current in L1 is
allowed to build up to an internally defined level
(nominally 320mA) before MN is turned off. The energy
stored in L1 is then transferred to the output capacitor
(C2) via schottky diode (D1). When the voltage on C2
has risen above the threshold voltage of the series
connected LEDs, current will flow through external
sense resistor R1. The voltage developed across R1 is
sensed at pin 'FB' and compared to a 100mV reference
voltage (V REF ). A comparator senses when the
feedback voltage is above VREF and its output is used to
control the 'off' time of the output switch. The control
loop is self-oscillating, producing pulses of up to 5␮s
maximum duration (switch 'on'), at a frequency that
varies in proportion to the LED current. The feedback
loop maintains a voltage of VREF at the FB pin and
therefore defines a maximum LED current equal to VREF
divided by R1. The minimum 'off' time of the output
switch is fixed at 0.5␮s nominal, to allow time for the
coil's energy to be dissipated before the switch is
turned on again. This maintains stable and efficient
operation in discontinuous mode.
Gated PWM operation
The internal circuitry of the ZXLD1100 is turned off
when no signal is present on the 'EN' pin for more than
120␮s (nominal). A low frequency signal applied to the
EN pin will therefore gate the device 'on' and 'off' at the
gating frequency and the duty cycle of this signal can
be varied to provide a 'chopped' output current equal
to (VREF/R1) x duty cycle. For best accuracy, the gating
frequency should be made as low as possible (e.g.
below 1kHz), such that the turn off delay of the chip is
only a small proportion of the gating period
Further details of setting output current are given in the
applications section under brightness control.
Open circuit protection
There is an internal avalanche diode between the
VSENSE and FB pins of the device. This diode, together
with the associated resistors provides open circuit
protection when the VSENSE pin is connected to the
output voltage. In the event of an open circuit
condition, the output voltage will rise above the
breakdown voltage of the internal diode, which will
then conduct and override the control signal from the
current sense resistor. This maintains the output
voltage at a level below the breakdown voltage of the
output switch. Supply current in this condition will fall
to a low value as the control loop provides only the bias
current for the diode.
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SEMICONDUCTORS
ZXLD1100
TYPICAL CHARACTERISTICS
(For typical application circuit at VIN=3V and TA=25 °C unless otherwise stated)
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ZXLD1100
TYPICAL OPERATING CHARACTERISTICS
(For typical applications circuit at VIN=3V, L=10␮H Coilcraft DO1608C Series, 3 series LEDs,
ILED=15mA, TA=25 °C unless otherwise stated)
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SEMICONDUCTORS
ZXLD1100
APPLICATIONS
Programming the maximum LED current
The maximum LED current is programmed by adding a
single resistor in series with the LED chain. The current
is determined by the resistor value and feedback
voltage and is given by:
Dimming Control using a DC voltage
For applications where the EN pin is not available a DC
voltage can be used to control dimming. By adding
resistors R2 and R3 and applying a DC voltage, the LED
current can be adjusted from 100% to 0%. As the DC
voltage increases, the voltage drop across R2 increases
and the voltage drop across R1 decreases, thus
reducing the current through the LEDs. Selection of R2
and R3 should ensure that the current from the DC
voltage is much less than the LED current and much
larger than the feedback current. The component
values in the diagram below represent 0% to 100%
dimming control from a 0 to 2V DC voltage.
ILED = VFB/R1
where VFB=100mV
The table below gives recommended resistor values
for required LED currents:
LED Current
R1 Value
10mA
10⍀
15mA
6.8⍀
20mA
5⍀
30mA
3.3⍀
Dimming Control via a PWM signal on the EN pin
A Pulse Width Modulated (PWM) signal can be applied
to the EN pin in order to adjust the output current to a
value below the maximum LED current. Two modes of
adjustment are possible as described below.
Dimming Control using a logic signal
For applications where the LED current needs to be
adjusted in discrete steps a logic signal can be applied
as shown in the diagram below. When Q1 os ‘off’, R1
sets the minimum LED current. When Q1 is ‘on’, R2 sets
the LED current that will be added to the minimum LED
current. The formula for selecting values for R1 and R2
are given below:
True Analog Dimming - Filtered ‘DC’ mode
If a PWM signal of 10kHz or higher is applied to the EN
pin, the device will remain active when the EN pin is
low. However, the input to the internal low pass filter
will be switched alternately from VREF to ground, with a
duty cycle (D) corresponding to that of the PWM signal.
This will present a filtered dc voltage equal to the duty
cycle multiplied by VREF to the control loop and will
produce a dc output current lower than the maximum
set value. This current is given by:
IOUTdc = 0.1D/R1
This mode of adjustment minimizes flicker in the light
output and system noise.
Pulsed Dimming - Gated Mode
If a lower frequency of 1kHz or less is applied to the EN
pin, the device will be gated ‘on’ and ‘off’ at a duty cycle
(D) corresponding to that of the input signal. The
average output current is then given by:
IOUTavg » 0.1D/R1
MOSFET ‘off’
I LED ( MIN )
This mode may be preferred over dc current control if
the purest white output is required. However, note the
120␮s nominal turn-off delay of the device, when using
the device in this mode.
V FB
RLED
MOSFET ‘on’
I LED ( MAX )
V FB
RLED
where VFB = 100mV
I LED ( MIN )
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SEMICONDUCTORS
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ZXLD1100
Open circuit protection
For maximum stability over temperature, capacitors
with X7R dielectric are recommended, as these have a
much smaller temperature coefficient than other types.
The voltage sense pin (VSENSE) can be connected to the
output to provide open circuit protection for the device
and external circuits when driving series connected
LEDs, thus eliminating the need for an external Zener
diode. Protection is provided by the internal avalanche
diode (ZD), which limits the maximum output voltage
to a value below the breakdown voltage of the output
switch when the connection to the diodes is broken.
A table of recommended manufacturers is provided
below:
Capacitor selection
A ceramic capacitor grounded close to the GND pin of
the package is recommended at the output of the
device. Surface mount types offer the best
performance due to their lower inductance. A
minimum value of 0.22␮F is advised, although higher
values will lower switching frequency and improve
efficiency especially at lower load currents. A higher
value will also minimize ripple when using the device
to provide an adjustable dc output current.
Manufacturer
Website
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Kemet
www.kement.com
AVX
www.avxcorp.com
A good quality, low ESR capacitor should also be used
for input decoupling, as the ESR of this capacitor is
effectively in series with the source impedance and
lowers overall efficiency. This capacitor has to supply
the relatively high peak current to the coil and smooth
the current ripple on the input supply. A minimum
value of 1␮F is acceptable if the input source is close to
the device, but higher values will improve performance
at lower input voltages, when the source impedance is
high. The input capacitor should be mounted as close
as possible to the IC
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SEMICONDUCTORS
ZXLD1100
Inductor selection
The choice of inductor will depend on available board
space as well as required performance. Small value
inductors have the advantage of smaller physical size
and may offer lower series resistance and higher
saturation current compared to larger values. A
disadvantage of lower inductor values is that they result
in higher frequency switching, which in turn causes
reduced efficiency due to switch losses. Higher inductor
values can provide better performance at lower supply
voltages. However, if the inductance is too high, the
output power will be limited by the internal oscillator,
which will prevent the coil current from reaching its
peak value. This condition will arise whenever the ramp
time (I LX(peak) x L/V IN ) exceeds the nominal 5␮s
maximum ‘on’ time limit for the LX output.
The graphs opposite show the ZXLD1100 performance
for given inductor values and different manufacturers.
Recommended inductor values for the ZXLD1100 are
in the range 6.8␮H to 22␮H. The inductor should be
mounted as close to the device as possible with low
resistance connections to the LX and VIN pins.
Suitable coils for use with the ZXLD1100 are shown in
the table below:
L
( H)
Part No.
DCR
( )
I SAT
(A)
Manufacturer
CMD4D11-100MC 10
0.457 0.5
Sumida
www.sumida.com
DO1608-103
10
0.16
1.1
Coilcraft
www.coilcraft.com
LQH31CN100
10
1.3
0.23
Murata
www.murata.com
LB2012Y100MR
10
0.5
0.1
Taiyo Yuden
www.t-yuden.com
Diode selection
Layout considerations
The rectifier diode (D1) should be a fast low
capacitance schottky diode with low reverse leakage at
the working voltage. It should also have a peak current
rating above the peak coil current and a continuous
current rating higher than the maximum output load
current.
PCB tracks should be kept as short as possible to
minimize ground bounce, and the ground pin of the
device should be soldered directly to the ground plane.
It is particularly important to mount the coil and the
input/output capacitors close to the device to minimize
parasitic resistance and inductance, which will
degrade efficiency. The FB pin is a high impedance
input so PCB track lengths to this should also be kept as
short as possible to reduce noise pickup. Excess
capacitance from the FB pin to ground should be
avoided.
The table below gives some typical characteristics for
diodes that can be used with the ZXLD1100:
Diode
V F @ 100mA (mV)
I FSM (mA)
Ic (mA)
I R at 30V ( A)
Package
ZHCS400
300
1000
400
15
SOD323
ZHCS500
300
1000
500
15
SOT23
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SEMICONDUCTORS
10
ZXLD1100
REFERENCE DESIGNS
3 LED Driver for Handset LCD Backlight
Circuit Diagram
Note: LED current is set to 15mA
Bill of materials
Ref
Value
U1
Package
Part Number
Manufacturer
Notes
SC70-6
ZXLD1100H6
Zetex
LED Driver IC
SOD323
ZHCS400
Zetex
400mA Schottky Diode
CMD4D11-100MC
Sumida
1mm Height Profile
Generic
Generic
D1
400mA
L1
10␮H
R1
6.8⍀
R2 1
100k⍀
0603
Generic
Generic
C1
1␮F
0603
Generic
Generic
C2
1␮F
0603
Generic
Generic
NSCW215
Nichia
LEDs
0603
3pcs per board
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1100 and LEDs. If EN pin can be driven low, R2 is not necessary.
Performance Graphs
ISSUE 4 - JULY 2004
11
SEMICONDUCTORS
ZXLD1100
4 LED Driver for Handset LCD Backlight
Circuit Diagram
Note: LED current is set to 15mA
Bill of materials
Ref
Value
U1
Package
Part Number
Manufacturer
Notes
SC70-6
ZXLD1100H6
Zetex
LED Driver IC
SOD323
ZHCS400
Zetex
400mA Schottky Diode
CMD4D11-100MC
Sumida
1mm Height Profile
Generic
Generic
D1
400mA
L1
10␮H
R1
6.8⍀
R2 1
100k⍀
0603
Generic
Generic
C1
1␮F
0603
Generic
Generic
C2
1␮F
0603
Generic
Generic
NSCW215
Nichia
LEDs
0603
4pcs per board
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1100 and LEDs. If EN pin can be driven low, R2 is not necessary.
Performance Graphs
ISSUE 4 - JULY 2004
SEMICONDUCTORS
12
ZXLD1100
5 LED Driver for Handset Main and Sub Display LCD Backlight
Circuit Diagram
Note: LED current is set to 15mA
Bill of materials
Ref
Value
U1
Package
Part Number
Manufacturer
Notes
SC70-6
ZXLD1100H6
Zetex
LED Driver IC
SOD323
ZHCS400
Zetex
400mA Schottky Diode
CMD4D11-100MC
Sumida
1mm Height Profile
Generic
Generic
D1
400mA
L1
10␮H
R1
6.8⍀
R2 1
100k⍀
0603
Generic
Generic
C1
1␮F
0603
Generic
Generic
C2
1␮F
0603
Generic
Generic
NSCW215
Nichia
LEDs
0603
5pcs per board
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1100 and LEDs. If EN pin can be driven low, R2 is not necessary.
Performance Graphs
ISSUE 4 - JULY 2004
13
SEMICONDUCTORS
ZXLD1100
6 LED Driver for LCD Backlight
Circuit Diagram
Note: LED current is set to 15mA
Bill of materials
Ref
Value
U1
Package
Part Number
Manufacturer
Notes
SC70-6
ZXLD1100H6
Zetex
LED Driver IC
SOD323
ZHCS400
Zetex
400mA Schottky Diode
CMD4D11-100MC
Sumida
1mm Height Profile
Generic
Generic
D1
400mA
L1
10␮H
R1
6.8⍀
R2 1
100k⍀
0603
Generic
Generic
C1
1␮F
0603
Generic
Generic
C2
1␮F
0603
Generic
Generic
NSCW215
Nichia
LEDs
0603
6pcs per board
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1100 and LEDs. If EN pin can be driven low, R2 is not necessary.
Performance Graphs
ISSUE 4 - JULY 2004
SEMICONDUCTORS
14
ZXLD1100
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15
SEMICONDUCTORS
ZXLD1100
PACKAGE OUTLINE - SC70-6
Controlling dimensions are in millimeters. Approximate conversions are given in inches
PACKAGE DIMENSIONS
Millimeters
Inches
DIM
Millimeters
Inches
DIM
Min
Max
Min
Max
A
0.80
1.10
0.0315
0.0433
E
A1
-
0.10
-
0.0039
E1
A2
0.80
1.00
0.0315
0.0394
e
b
0.15
0.30
0.006
0.0118
e1
C
0.08
0.25
0.0031
0.0098
L
0.26
0.46
0.0102
0.0181
a°
0°
8°
0°
8°
D
2.00 BSC
0.0787 BSC
Min
Max
2.10BSC
1.25
1.35
0.65 BSC
1.30 BSC
Min
Max
0.0826 BSC
0.0492
0.0531
0.0255 BSC
0.0511 BSC
© Zetex plc 2003
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SEMICONDUCTORS
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SCZXLD1100DS2