Zetex (Now Diodes) ZXLD1101 Schematic [ru]
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ZXLD1101
ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH IN TSOT23-5
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 60 A and a shutdown function is provided to reduce this current to less than 500nA in the 'off' state.
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.
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: (60 A typ)
•500nA maximum shutdown current
•Up to 1MHz switching frequency
•Low external component count
•Inherently matched LED currents
APPLICATIONS
•Mobile phones
•Digital cameras
•PDAs
•LCD modules
•Portable internet appliances
•Palmtop computers
TYPICAL APPLICATION CIRCUIT
PIN CONNECTIONS
ISSUE 4 - JULY 2004
1 |
SEMICONDUCTORS |
ZXLD1101
ORDERING INFORMATION
DEVICE |
DEVICE DESCRIPTION |
TEMPERATURE RANGE |
PART MARK |
TAPING |
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OPTIONS |
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ZXLD1101ET5 |
Boost converter in TSOT23-5 |
-40°C to +85°C |
1101 |
TA, TC |
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ZXLD1101ET5TA for 7” reel of 3,000 devices
ZXLD1101ET5TA for 13” reel of 10,000 devices
ABSOLUTE MAXIMUM RATINGS (Voltages to GND unless otherwise stated)
PARAMETER |
SYMBOL |
LIMIT |
UNIT |
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Input voltage |
(VIN) |
7 |
V |
LX output voltage |
(VLX) |
30 |
V |
Switch output current |
(ILX) |
500 |
mA |
Power dissipation |
(PD) |
300 |
mW |
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Operating temperature |
(TOP) |
-40 to 85 |
°C |
Storage temperature |
(TST) |
-55 to 150 |
°C |
Junction temperature |
(Tj MAX) |
125 |
°C |
ISSUE 4 - JULY 2004
SEMICONDUCTORS |
2 |
ZXLD1101
ELECTRICAL CHARACTERISTICS (at VIN = 3V, Tamb = 25°C unless otherwise stated(1))
SYMBOL |
PARAMETER |
CONDITIONS |
MIN. |
TYP. |
MAX. |
UNIT |
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VIN |
Input voltage |
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2.5 |
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5.5 |
V |
IIN |
Supply current |
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Quiescent |
VEN = VIN, ILX = 0, |
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60 |
100 |
A |
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Output not switching |
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Shutdown |
VEN = 0V |
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500 |
nA |
VFB |
FB pin control voltage |
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90.5 |
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109.5 |
mV |
IFB |
FB pin input current |
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100 |
nA |
fLX |
Operating frequency |
L=10 H, VOUT =10V, |
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0.35 |
1 |
MHz |
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IOUT=20mA |
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TOFF |
LX output 'OFF' time |
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350 |
500 |
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ns |
TON |
LX output 'ON' time (2) |
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5 |
µs |
ILXpk |
Switch peak current limit |
L=10 H, VOUT =10V, |
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320 |
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mA |
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IOUT=20mA |
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RLX |
Switch 'On' resistance |
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1.5 |
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ILX(leak) |
Switch leakage current |
VLX =20V |
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1 |
µA |
VOUT |
Controller output voltage |
Normal operation |
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28 |
V |
VENH |
EN pin High level Input voltage |
Device active |
1.5 |
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VIN |
V |
VENL |
EN pin Low level Input voltage |
Device in shutdown |
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0.4 |
V |
IENL |
EN pin Low level input current |
VEN =0V |
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-100 |
nA |
IENH |
EN pin High level input current |
VEN =VIN |
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1 |
A |
TEN(hold) |
EN pin turn off delay (3) |
VEN switched from high |
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120 |
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µs |
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to low |
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∆T/T |
PWM duty cycle range at ‘EN’ input for |
10kHz < f < 100kHz, |
20 |
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100 |
% |
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filtered PWM control (4) |
VENH =VIN |
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fLPF |
Internal PWM low pass filter cut-off |
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4 |
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kHz |
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frequency |
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ALPF |
Filter attenuation |
f=30kHz |
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52.5 |
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dB |
∆T/T |
PWM duty cycle range at ‘EN’ input for |
f < 1kHz, VENH =VIN |
0 |
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100 |
% |
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‘gated’ output current control (5) |
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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).
ISSUE 4 - JULY 2004
3 |
SEMICONDUCTORS |
ZXLD1101
PIN DESCRIPTION
PIN NO. |
NAME |
DESCRIPTION |
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1 |
FB |
Feedback pin for current control loop (connect resistor R1 |
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from this pin to GND for output current I=100mV/ R1) |
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2 |
GND |
Ground (0V) |
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3 |
LX |
Output of NDMOS switch |
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4 |
VIN |
Input voltage (2.5V to 5.5V). Decouple with capacitor close |
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to device |
5 |
EN |
Enable input (active high to turn on device) |
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Also used to adjust output current by PWM signal |
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Connect to Vin for permanent operation |
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BLOCK DIAGRAM
ISSUE 4 - JULY 2004
SEMICONDUCTORS |
4 |
ZXLD1101
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 (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 (VREF). 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.
ISSUE 4 - JULY 2004
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
Gated PWM operation
The internal circuitry of the ZXLD1101 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.
5 |
SEMICONDUCTORS |
ZXLD1101
TYPICAL CHARACTERISTICS
(For typical application circuit at VIN=3V and TA=25°C unless otherwise stated)
ISSUE 4 - JULY 2004
SEMICONDUCTORS |
6 |