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PDF ZXLD1100 Data sheet ( Hoja de datos )
| Número de pieza | ZXLD1100 | |
| Descripción | ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH AND OPEN CIRCUIT PROTECTION | |
| Fabricantes | Zetex | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de ZXLD1100 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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www.DataSheet4U.com
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.
Quiescent current is typically 60A 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 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.
The device is assembled in a low profile SC70-6 pin
package with industry standard pinout.
ADVANCED FEATURES
• Internal 30V NDMOS switch, current sense and
open circuit protection
• True Analog Dimming via PWM
FEATURES
• 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: (60A 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
PROVISIONAL SPEC ISSUE A - AUGUST 2003
1
SEMICONDUCTORS
1 page  
www.DataSheet4U.com
ZXLD1100
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 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
therefore defines a maximum LED current equal to VREF
divided by R1. The minimum 'off' time of the output
switch is fixed at 0.5ms 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
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 ZXLD1100 is turned off
when no signal is present on the 'EN' pin for more than
120s (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.
PROVISIONAL SPEC ISSUE A - AUGUST 2003
5
SEMICONDUCTORS
5 Page 
REFERENCE DESIGNS
3 LED Driver for Handset LCD Backlight
Circuit Diagram
www.DataSheet4U.com
ZXLD1100
Note: LED current is set to 15mA
Bill of materials
Ref
U1
D1
L1
R1
R21
C1
C2
LEDs
Value
400mA
10H
6.8⍀
100k⍀
1F
1F
Package
SC70-6
SOD323
0603
0603
0603
0603
Part Number
ZXLD1100H6
ZHCS400
CMD4D11-100MC
Generic
Generic
Generic
Generic
NSCW215
Manufacturer
Zetex
Zetex
Sumida
Generic
Generic
Generic
Generic
Nichia
Notes
LED Driver IC
400mA Schottky Diode
1mm Height Profile
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
PROVISIONAL SPEC ISSUE A - AUGUST 2003
11
SEMICONDUCTORS
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet ZXLD1100.PDF ] | |
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