1
SEMICONDUCTORS
DESCRIPTION
The ZXLD1101 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 ZXLD1101 includes the output switch and peak
current sense resistor, and can operate with a
maximum output voltage of 28V.
Quiescent current is typically 60A and a shutdown
function is provided to reduce this current to less than
500nA in the 'off' state.
ADVANCED FEATURES
•True Analog Dimming via PWM
FEATURES
•1mm height profile TSOT23-5 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: (60A typ)
•500nA maximum shutdown current
•Up to 1MHz switching frequency
•Low external component count
•Inherently matched LED currents
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.
The device is assembled in the TSOT23-5 pin package
with 1mm maximum height profile.
APPLICATIONS
•Mobile phones
•Digital cameras
•PDAs
•LCD modules
•Portable internet appliances
•Palmtop computers
ZXLD1101
ISSUE 4 - JULY 2004
ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH IN TSOT23-5
PIN CONNECTIONS
TYPICAL APPLICATION CIRCUIT
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ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
2
PARAMETER SYMBOL LIMIT UNIT
Input voltage (VIN)7V
LX output voltage (VLX)30V
Switch output current (ILX) 500 mA
Power dissipation (PD) 300 mW
Operating temperature (TOP) -40 to 85 °C
Storage temperature (TST) -55 to 150 °C
Junction temperature (Tj MAX) 125 °C
ABSOLUTE MAXIMUM RATINGS (Voltages to GND unless otherwise stated)
DEVICE DEVICE DESCRIPTION TEMPERATURE RANGE PART MARK TAPING
OPTIONS
ZXLD1101ET5 Boost converter in TSOT23-5 -40°C to +85°C 1101 TA, TC
ORDERING INFORMATION
ZXLD1101ET5TA for 7” reel of 3,000 devices
ZXLD1101ET5TA for 13” reel of 10,000 devices
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ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
3
SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
VIN Input voltage 2.5 5.5 V
IIN Supply current
Quiescent
Shutdown
VEN =V
IN,I
LX =0,
Output not switching
VEN =0V
60 100
500
A
nA
VFB FB pin control voltage 90.5 109.5 mV
IFB FB pin input current 100 nA
fLX Operating frequency L=10H, VOUT =10V,
IOUT=20mA 0.35 1 MHz
TOFF LX output 'OFF' time 350 500 ns
TON LX output 'ON' time (2) 5µs
ILXpk Switch peak current limit L=10H, VOUT =10V,
IOUT=20mA 320 mA
RLX Switch 'On' resistance 1.5 ⍀
ILX(leak) Switch leakage current VLX =20V 1 µA
VOUT Controller output voltage Normal operation 28 V
VENH EN pin High level Input voltage Device active 1.5 VIN V
VENL EN pin Low level Input voltage Device in shutdown 0.4 V
IENL EN pin Low level input current VEN =0V -100 nA
IENH EN pin High level input current VEN =VIN 1A
TEN(hold) EN pin turn off delay (3) VEN switched from high
to low 120 µs
∆T/T PWM duty cycle range at ‘EN’ input for
filtered PWM control (4) 10kHz < f < 100kHz,
VENH =VIN 20 100 %
fLPF Internal PWM low pass filter cut-off
frequency 4 kHz
ALPF Filter attenuation f=30kHz 52.5 dB
∆T/T PWM duty cycle range at ‘EN’ input for
‘gated’ output current control (5) f < 1kHz, VENH =VIN 0 100 %
ELECTRICAL CHARACTERISTICS (at VIN = 3V, Tamb = 25°C unless otherwise stated(1))
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, characterisation 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) 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.
(4)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.
(5)The maximum PWM signal frequency during this mode of operation should be kept as low as possible to minimise errors due to the turn-off
delay of the device (see Enable pin turn-off delay).
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ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
4
BLOCK DIAGRAM
PIN NO. NAME DESCRIPTION
1 FB Feedback pin for current control loop (connect resistor R1
from this pin to GND for output current I=100mV/ R1)
2 GND Ground (0V)
3 LX Output of NDMOS switch
4V
IN Input voltage (2.5V to 5.5V). Decouple with capacitor close
to device
5 EN Enable input (active high to turn on device)
Also used to adjust output current by PWM signal
Connect to Vin for permanent operation
PIN DESCRIPTION
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DEVICE DESCRIPTION
The device is a PFM flyback dc-dc boost converter,
working in discontinuous mode.
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
(nominally320mA)beforeMNisturnedoff.Theenergy
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 (VREF). A comparator senses when the
feedbackvoltageisaboveVREF 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 5s
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
thereforedefinesamaximumLEDcurrentequaltoVREF
divided by R1. The minimum 'off' time of the output
switch is fixed at 0.5s 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.
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
highstateonENthereforeprovidesafilteredvoltageof
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
Gated PWM operation
The internal circuitry of the ZXLD1101 is turned off
whenno signal is presenton the'EN'pinformore than
120s (nominal). A low frequency signal applied to the
ENpinwillthereforegate thedevice'on'and'off'atthe
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
Furtherdetailsofsettingoutputcurrentaregiveninthe
applications section under brightness control.
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
5
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APPLICATIONS
Programming the maximum LED current
ThemaximumLEDcurrentisprogrammedbyaddinga
singleresistor in serieswiththeLED chain. The current
is determined by the resistor value and feedback
voltage and is given by:
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.
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
willbeswitchedalternatelyfrom VREF to ground,witha
dutycycle(D)correspondingto thatofthePWMsignal.
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,thedevicewillbegated'on'and'off'at adutycycle
(D) corresponding to that of the input signal. The
average output current is then given by:
IOUTavg »0.1D/R1
This mode may be preferred over dc current control if
the purest white output is required. However, note the
120snominalturn-offdelayofthe device, whenusing
the device in this mode.
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
8
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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
resistorsR2 and R3andapplyinga DC voltage,theLED
current can be adjusted from 100% to 0%. As the DC
voltageincreases,thevoltagedropacrossR2increases
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.
Dimming Control using a filtered PWM signal
The filtered PWM signal can be considered as an
adjustable DC voltage by applying a RC filter. The
values shown in the diagram below are configured to
give 0% to 100% dimming for a 1kHz to 100kHz PWM
signal with a 2V amplitude. e.g. a 50% duty cycle will
give 50% dimming.
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
setstheminimumLEDcurrent.WhenQ1is'on',R2sets
theLED current that will beaddedtotheminimumLED
current. The formula for selecting values for R1 and R2
are given below:
MOSFET ‘off’
IV
R
LED MIN FB
LED
()
=
MOSFET ‘on’
IV
RI
LED MAX LED LED MIN
FB
() ()
=+
where VFB = 100mV
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
9
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Open circuit protection
For applications where the LED chain can go
open-circuitaZenerdiodecanbe connected acrossthe
LED chain preventing over-voltage and possible
damage to the main switching transistor. The Zener
diodes should be selected by ensuring its voltage
rating is higher than the combined forward voltage of
the LED chain. Under open circuit conditions the
current in the Zener diode defines the output current
as:
IVR
ZFB
Z
=
To limit battery drain in this fault condition the Zener
diode current should be less than 1mA.
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 0.22F is advised, although higher
values will lower switching frequency and improve
efficiency especially at lower load currents. A higher
value will also minimise ripple when using the device
to provide an adjustable dc output current.
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 1F is acceptable if the input source is close to
thedevice,buthighervalueswillimproveperformance
at lower input voltages, when the source impedance is
high. The input capacitor should be mounted as close
as possible to the IC.
For maximum stability over temperature, capacitors
with X7R dielectric are recommended, as these have a
muchsmallertemperaturecoefficientthanothertypes.
A table of recommended manufacturers is provided
below:
Manufacturer Website
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Kemet www.kement.com
AVX www.avxcorp.com
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
10
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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
disadvantageoflowerinductorvaluesisthattheyresult
in higher frequency switching, which in turn causes
reducedefficiencydue to switch losses.Higherinductor
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 (ILX(peak) xL/V
IN) exceeds the nominal 5s
maximum 'on' time limit for the LX output.
The graphs opposite show the ZXLD1101 performance
forgiveninductorvaluesanddifferentmanufacturers.
Recommended inductor values for the ZXLD1101 are
in the range 6.8H to 22H. 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 ZXLD1101 are shown in
the table below:
Part No. L
(H) DCR
( ) ISAT
(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.co
Diode selection
The rectifier diode (D1) should be a fast low
capacitanceschottky diode with low reverseleakage 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.
The table below gives some typical characteristics for
diodes that can be used with the ZXLD1101:
Diode VF@ 100mA (mV) IFSM (mA) Ic (mA) IRat 30V ( A) Package
ZHCS400 300 1000 400 15 SOD323
ZHCS500 300 1000 500 15 SOT23
Layout considerations
PCB tracks should be kept as short as possible to
minimise ground bounce, and the ground pin of the
deviceshouldbesoldereddirectlyto the groundplane.
It is particularly important to mount the coil and the
input/outputcapacitors close to the deviceto minimise
parasitic resistance and inductance, which will
degrade efficiency. The FB pin is a high impedance
inputsoPCB tracklengthstothisshouldalsobekeptas
short as possible to reduce noise pickup. Excess
capacitance from the FB pin to ground should be
avoided.
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
11
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REFERENCE DESIGNS
3 LED Driver for Handset LCD Backlight
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
12
Circuit Diagram
Performance Graphs
Ref Value Package Part Number Manufacturer Notes
U1 TSOT23-5 ZXLD1101ET5 Zetex LED Driver IC
D1 400mA SOD323 ZHCS400 Zetex 400mA Schottky Diode
L1 10H CMD4D11-100MC Sumida 1mm Height Profile
R1 6.8⍀0603 Generic Generic
R21100k⍀0603 Generic Generic
C1 1F 0603 Generic Generic
C2 1F 0603 Generic Generic
LEDs NSCW215 Nichia 3pcs per board
Bill of materials
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1101 and LEDs. If EN pin can be driven low, R2 is not necessary.
Note: LED current is set to 15mA
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4 LED Driver for Handset LCD Backlight
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
13
Circuit Diagram
Performance Graphs
Ref Value Package Part Number Manufacturer Notes
U1 TSOT23-5 ZXLD1101ET5 Zetex LED Driver IC
D1 400mA SOD323 ZHCS400 Zetex 400mA Schottky Diode
L1 10H CMD4D11-100MC Sumida 1mm Height Profile
R1 6.8⍀0603 Generic Generic
R21100k⍀0603 Generic Generic
C1 1F 0603 Generic Generic
C2 1F 0603 Generic Generic
LEDs NSCW215 Nichia 4pcs per board
Bill of materials
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.
Note: LED current is set to 15mA
Last Time Buy
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5 LED Driver for Handset Main and Sub Display LCD Backlight
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
14
Circuit Diagram
Performance Graphs
Ref Value Package Part Number Manufacturer Notes
U1 TSOT23-5 ZXLD1101ET5 Zetex LED Driver IC
D1 400mA SOD323 ZHCS400 Zetex 400mA Schottky Diode
L1 10H CMD4D11-100MC Sumida 1mm Height Profile
R1 6.8⍀0603 Generic Generic
R21100k⍀0603 Generic Generic
C1 1F 0603 Generic Generic
C2 1F 0603 Generic Generic
LEDs NSCW215 Nichia 5pcs per board
Bill of materials
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1101 and LEDs. If EN pin can be driven low, R2 is not necessary.
Note: LED current is set to 15mA
Last Time Buy
Closest Alternative is AP5724WUG-7
6 LED Driver for LCD Backlight
ZXLD1101
SEMICONDUCTORS
ISSUE 4 - JULY 2004
15
Circuit Diagram
Performance Graphs
Ref Value Package Part Number Manufacturer Notes
U1 TSOT23-5 ZXLD1101ET5 Zetex LED Driver IC
D1 400mA SOD323 ZHCS400 Zetex 400mA Schottky Diode
L1 10H CMD4D11-100MC Sumida 1mm Height Profile
R1 6.8⍀0603 Generic Generic
R21100k⍀0603 Generic Generic
C1 1F 0603 Generic Generic
C2 1F 0603 Generic Generic
LEDs NSCW215 Nichia 6pcs per board
Bill of materials
Note: R2 is optional. If EN is floating add R2 to shutdown the ZXLD1101 and LEDs. If EN pin can be driven low, R2 is not necessary.
Note: LED current is set to 15mA
Last Time Buy
Closest Alternative is AP5724WUG-7
ZXLD1101
SEMICONDUCTORS
16
ISSUE 4 - JULY 2004
Europe
Zetex plc
Fields New Road
Chadderton
Oldham, OL9 8NP
United Kingdom
Telephone (44) 161 622 4444
Fax: (44) 161 622 4446
hq@zetex.com
Zetex GmbH
Streitfeldstraße 19
D-81673 München
Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
europe.sales@zetex.com
Americas
Zetex Inc
700 Veterans Memorial Hwy
Hauppauge, NY 11788
USA
Telephone: (1) 631 360 2222
Fax: (1) 631 360 8222
usa.sales@zetex.com
Asia Pacific
Zetex (Asia) Ltd
3701-04 Metroplaza Tower 1
Hing Fong Road
Kwai Fong
Hong Kong
Telephone: (852) 26100 611
Fax: (852) 24250 494
asia.sales@zetex.com
These offices are supported by agents and distributors in major countries world-wide.
Thispublicationisissuedtoprovide outlineinformationonlywhich (unlessagreedbythe Companyinwriting)may notbeused,applied orreproduced
for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company
reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service.
For the latest product information, log on to www.zetex.com
© Zetex plc 2003
SCZXLD1101DS2
DIM Millimeters Inches DIM Millimeters Inches
Min Max Min Max 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 0.0037 BSC
A2 0.84 0.90 0.0330 0.0354 e1 1.90 BSC 0.074 BSC
b 0.30 0.45 0.0118 0.0177 L 0.30 0.50 0.0118 0.0196
c 0.12 0.20 0.0047 0.0078 L2 0.25 BSC 0.010 BSC
D 2.90 BSC 0.114 BSC a° 4° 12° 4° 12°
E 2.80 BSC 0.110 BSC - ----
PACKAGE DIMENSIONS
Controlling dimensions are in millimeters. Approximate conversions are given in inches
PACKAGE OUTLINE - TSOT23-5
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