ZXLD1321DCATC Diodes Zetex, ZXLD1321DCATC Datasheet - Page 17

• Manufacturer Part Number: ZXLD1321DCATC
• Description: IC LED DRVR WHITE BCKLGT 14-TDFN
• Manufacturer: Diodes Zetex
• Type: Backlight, White LEDr

Specifications of ZXLD1321DCATC

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: High Brightness LED (HBLED), White LED
• Frequency: 600kHz
• Voltage - Supply: 2 V ~ 12 V
• Mounting Type: Surface Mount
• Package / Case: 14-TDFN
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• Efficiency: 85%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Other names: ZXLD1321DCATR

The LED current is sensed by R3 and the controller varies this until the drop in R3 equals 20% of
VADJ. Hence making R3 = 100m
500mV VADJ results in 100mV across R3 which equals 1 Amp. Making VADJ = 10mV gives a LED
current of 100mA because the 50mV VADJ results in 10mV drop across R3 which equals 100mA.
The power is controlled by the chip backing off the peak coil current, so it is necessary to calculate
the coil inductance and current to guarantee slightly more than 100% LED power, so the circuit
can control it effectively. The internal control loop is compensated by C1, which is normally 10nF.
Note that in Bootstrap mode, the input current will be 2 or 3 times larger than the LED current and
the duty cycle will be such that TON is larger than TOFF, due to the fact that the supply voltage
charging the coil is low. Because of this, large LED currents can not be programmed at very low
supply voltages, as the transistor current would need to exceed 2 Amps.
If the thermistor (R5) is used, the power will be backed off progressively as the TADJ pin goes low.
With the TADJ pin above 75mV, power is 100% and this is reduced to zero when the TADJ pin
reaches 50mV. Making R4 = 5k
869
125°C the thermistor will reach 547
protect the LED from damage. These temperature values can be set by the customer by using a
different thermistor or a different value of R4. If protection is not required, leaving the TADJ pin
open circuit will make it float to a high voltage and always give 100% power.
Issue 1 - January 2008
© Zetex Semiconductors plc 2008
Reference
U1
D1
C1
C2
C3
R1
R2
R3
R4
R5
L1
L1
L1
at 105°C giving TADJ = 74mV which will start to reduce the LED power above 105°C. By
GRM31MR71E225K
GRM31CR71H475K
NPIS64D100MTRF
MSS7341-103ML
Thermistor NTC
744 777910
ZXLD1321
ZXCS2000
Part No
Generic
Generic
Generic
Generic
Generic
and VADJ = 500mV gives a LED current of 1 Amp because the
and using a 103KT1608 thermistor, the thermistor will reach
giving TADJ = 50mV which gives zero power. This will
Schottky diode
LED Driver
4.7µF 50V
2.2µF 25V
10nF 10V
10µH 2A
10µH 2A
10µH 2A
100m
Value
25m
5.1k
10k
17
Manufacturer
Generic 0805
Generic 0603
Generic 0805
Generic 0603
Murata 1206
Murata 1206
103kt1608
Coilcraft
Generic
Wurth
Zetex
Zetex
NIC
ZXLD1321
www.murata.com
www.murata.com
www.wurth.co.uk
Contact Details
www.coilcraft.co
www.zetex.com
www.zetex.com
www.niccomp
m