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PDF ZXLD1320 Data sheet ( Hoja de datos )
| Número de pieza | ZXLD1320 | |
| Descripción | Buck mode DC-DC converter | |
| Fabricantes | Zetex Semiconductors | |
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ZXLD1320
Buck mode DC-DC converter for LED driving with
1.5A output and current control
Description
The ZXLD1320 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 1.5A output current.
Applications cover both commercial and
automotive environments with input voltages
ranging from 4V to 18V. Depending upon
supply voltage and external components, this
can provide up to 24W of output power.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and operates in the
step-down (Buck) operating mode, offering
higher power efficiency and lower system
cost than conventional PFM 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
ZXLD1320 provides excellent load and current
regulation, resulting in very stable LED current
over the full operating voltage and 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 'Power-OK' (POK) output flag remains high
during normal operation, but switches low if the
switch transistor remains on for more than
500μs. This provides indication of a low battery,
or fault condition. The POK output may be used
to drive an LED or the input of an MCU.
The device can be shut down by applying a
continuous low level dc voltage to the ADJ pin.
Features
• Step-down LED driver
• 4V to 18V input voltage range
• Up to 1.5A output current
• Typical efficiency# > 85%
• 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
• Power 'OK' flag output
• Capable of driving 4 LEDs in series
Applications
• Low voltage halogen lamp replacement
with LEDs
• High power LED flashlights
• LED back-up lighting
• General LED lighting
• Automotive 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
ZXLD1320
Electrical characteristics (Test conditions: VIN = 4V, TAMB= 25°C unless otherwise stated(a))
DC-DC converter supply parameters
Symbol
VIN
Iq
ISTBY
VREF
TCO(REF)
Parameter
Supply voltage
Quiescent current
Standby current
Internal reference voltage
Internal reference temperature
coefficient.
Conditions
Normal operation
Measured into VIN
ADJ pin floating.
(Excluding switch
base current).
Measured into VIN.
ADJ pin grounded
ADJ pin floating
2.0V<VIN<18V
Min
4.0
480
Typ Max Units
18 V
1.5 mA
12 20 µA
500 520 mV
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° Care guaranteed by design, characterisation and process control.
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
ISENSE
Sense input current
Measured into
-15 -7
ISENSE with pin at
0V.
CFB pin at 0V
-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) Internal clamp voltage on ADJ 100µA injected into 575 mV
pin ADJ pin
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
5
www.zetex.com
Datasheet pdf - http://www.DataSheet4U.net/
5 Page 
www.DataSheet.co.kr
ZXLD1320
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 MVIN and M_LOAD.
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 ZXLD1320.PDF ] | |
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