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PDF ZXLD1322 Data sheet ( Hoja de datos )
| Número de pieza | ZXLD1322 | |
| Descripción | Buck/boost mode DC-DC converter | |
| Fabricantes | Zetex Semiconductors | |
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ZXLD1322
Buck/boost mode DC-DC converter for LED driving
with 700mA output and current control
Description
The ZXLD1322 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 700mA output current.
Applications cover input voltages ranging
from 2.5V to 15V. Depending upon supply
voltage and external components, this can
provide up to 12W of output power.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and operates in Buck/
Boost mode, offering higher power efficiency
and lower system cost than conventional PFM
buck/boost circuitry.
The device includes the DC-DC converter, a
high-side current monitor and an NPN
switching transistor to provide an integrated
solution offering small PCB size, competitive
cost/performance, high power efficiency of
DC-DC conversion and maximum LED
brightness/reliability. More importantly, it
retains design flexibility to add customer
specific features.
The feedback control circuitry inside the
ZXLD1322 provides excellent load and current
regulation, resulting in very stable LED current
over the useful life of the battery and over the
full operating temperature range.
The LED current can be adjusted from 100%
down to 10% of the set value by applying a dc
voltage to the ADJ pin and down to 1% by
applying a PWM signal. An on-chip LED
protection circuit also allows output current to
be reduced linearly above a predetermined
threshold temperature using an external
thermistor at the TADJ pin.
External resistors set nominal average LED
current and coil peak current independently.
The device can be shut down by applying a
continuous low level dc voltage to the ADJ pin.
Features
• 2.5V to 15V Input Voltage Range
• Up to 700mA output current
• Typical efficiency# >80%
• User-defined thermal control of LED
output current using external thermistor
• High output current stability over input
voltage and temperature
• 12µA typical standby current
• LED current adjustable from 100%
down to 2%
• Adjustable Soft-Start
• Capable of driving 3 LEDs in series
Applications
• High power LED flashlights
• LED back-up lighting
• General LED lighting
Note# : Using standard external components as specified under electrical characteristics. Efficiency is dependent upon
external component types and values. Higher efficiency is possible with alternative coils.
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
1
www.zetex.com
Datasheet pdf - http://www.DataSheet4U.net/
1 page  
www.DataSheet.co.kr
ZXLD1322
Electrical characteristics (Test conditions: VIN = 4V, TAMB= 25°C unless otherwise stated(a))
DC-DC converter supply parameters
Symbol Parameter
Conditions
Min Typ Max Units
VIN Supply voltage
Normal operation 2.5
15 V
VIN(Start) Supply voltage for start-up(b)
Start-up mode
1.2
2.4 V
VUV-
Under-voltage detection threshold VIN falling
normal operation to start-up mode
1.8 V
VUV+
Under-voltage detection threshold VIN rising
start-up mode to normal operation
2.2 V
Iq Quiescent current
Measured into VIN
ADJ pin floating.
(Excluding switch
base current).
1.5
mA
ISTBY
Standby current
Measured into VIN.
ADJ pin grounded
12 20 µA
VREF
Internalreference voltage
ADJ pin floating
2.5V<VIN<15V
480 500 520 mV
TCO(REF) Internal reference temperature
coefficient.
50 ppm
/K
NOTES:
(a) Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified from -40°C to
+125°C are guaranteed by design, characterisation and process control.
(b) Between 1.2V and 2.2V the device will run in the Low Voltage Startup Mode (for details refer to section "Low Voltage Operation")
DC-DC converter input parameters
Symbol Parameter
Conditions
Min Typ Max Units
VSENSE
Peak switch current sense
voltage
Measured on ISENSE 45 55 65 mV
pin CFB pin at 0V
VSENSE
(SU)
Peak switch current sense
voltage in start-up mode
Measured on ISENSE
pin.
Start-up mode
VIN=1.2V
10.5
mV
ISENSE
Sense input current
Measured into
ISENSE with pin at
0V.CFB pin at 0V
-15 -7
-1 µA
CFB Control loop compensation
capacitor
10 nF
VADJ
External dc control voltage
applied to ADJ pin to adjust
output current
DC brightness
control mode
50
500 mV
VADJ(th)
Switching threshold of ADJ pin Standby state to
Normal operation
26 28 30 mV
TCO(VADJ) Temperature coefficient of
VADJ(th)
+0.3
%/K
RADJ
Internal resistor between VREF VADJ<500mV
and ADJ
100 kΩ
VADJ(clmp) Clamp voltage on ADJ pin
100µA injected into
ADJ pin
575 mV
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
5
www.zetex.com
Datasheet pdf - http://www.DataSheet4U.net/
5 Page 
www.DataSheet.co.kr
ZXLD1322
Application notes
Setting peak coil current
The peak current in the coil is set by the resistor (RSENSE) between the switch emitter and ground
according to
I SWpeak
=
50mV
Rsense
The minimum peak current will depend on operating mode, coil inductance and supply voltage
range. The maximum peak current must not exceed the specified value for the switch. (See
Application circuits for details)
Setting LED current
The nominal average LED current is given by
I LED (nom)
=
100mV
RM
Where RM is the external resistor connected between pins M_VIN and VIN.
This current can be adjusted to a lower value by applying a dc control voltage or PWM control
signal to the ADJ pin.
DC control
The LED current can be adjusted over a 10% to 100% range by connecting a variable resistor RADJ
from the ADJ pin to ground to vary the dc voltage at the ADJ pin. RADJ forms the lower part of a
resistive divider and the internal 100kΩ resistor between the ADJ and VREF pins forms the upper
part. A value of 1MΩ for RADJ will therefore give a maximum current of 91% of ILED (nom) and the
device will be turned off when the voltage on the ADJ pin falls below 28mV, corresponding to an
RADJ value of approximately 5kΩ. If required, an end-stop resistor in series with RADJ can be used
to maintain the voltage on the ADJ pin above the turn-on threshold.
Using a logarithmic potentiometer for RADJ will give an approximately linear variation of output
current with shaft rotation. (Fig 1)
If required, the maximum output current can be restored to 100% by adjusting the value of the
LED current monitor resistor (RM). The tolerance of the internal 100k resistor and RADJ should be
taken into account when calculating output current.
The ADJ pin is clamped internally to a voltage of 575mV (nom), to limit maximum average output
current to approximately 115% of ILED(nom).
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
11
www.zetex.com
Datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet ZXLD1322.PDF ] | |
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