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PDF ZXLD1321 Data sheet ( Hoja de datos )
| Número de pieza | ZXLD1321 | |
| Descripción | Buck mode DC-DC converter | |
| Fabricantes | Zetex Semiconductors | |
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ZXLD1321
Boost mode DC-DC converter for LED driving with 1A
output and current control
Description
The ZXLD1321 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 1A output current.
Applications cover commercial environments
with input voltages ranging from 1.2V to 12V.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and supports step-up
(Boost) mode and self-powering Bootstrap
operating modes, 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
ZXLD1321 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 to the ADJ pin. 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
• 1.2V to 12V Input voltage range
• Up to 1A output current
• Typical efficiency# >85%
• Bootstrap operation enables input voltage
down to 1V
• 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
• Drives up to 5 white LEDs in series
Applications
• High power LED flashlights
• LED back-up lighting
• General LED lighting
• Emergency 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
ZXLD1321
Electrical characteristics (Test conditions: VIN = 3V, TAMB= 25°C unless otherwise stated(a))
DC-DC converter supply parameters
Symbol Parameter
Conditions
Min Typ Max Units
VIN Supply voltage
Normal operation 2.0
12 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
Internal reference voltage
ADJ pin floating
2.0V<VIN<18V
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
VSENSE
VSENSE
(SU)
Parameter
Peak switch current sense
voltage
Peak switch current sense
voltage in start-up mode
ISENSE
Sense input current
CFB Control loop compensation
capacitor
VADJ
External dc control voltage
applied to ADJ pin to adjust
output current
VADJ(th)
Switching threshold of ADJ
pin
TCO(VADJ) Temperature coefficient of
VADJ(th)
RADJ
Internal resistor between
VREF and ADJ
VADJ(clmp) Clamp voltage on ADJ pin
Conditions
Measured on ISENSE
pin CFB pin at 0V
Measured on ISENSE
pin.
Start-up mode
VIN=1.2V
Measured into
ISENSE with pin at
0V. CFB pin at 0V
Min
45
-15
DC brightness
control mode
Standby state to
normal operation
50
26
VADJ<500mV
100µA injected into
ADJ pin
Typ Max Units
55 65 mV
10.5 mV
-7 -1 µA
10 nF
500 mV
28 30 mV
+0.3
%/K
100 kΩ
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
ZXLD1321
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 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 | ||
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