ZXLD1374_11 DIODES [Diodes Incorporated], ZXLD1374_11 Datasheet - Page 27

• Manufacturer Part Number: ZXLD1374_11
• Description: 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST
• Manufacturer: DIODES [Diodes Incorporated]

ZXLD1374
Document number: DS35032 Rev. 2 - 2
Applications Information
The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open
collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the
circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status pin
will go down to GND while the FLAG and REF pins will stay at their nominal values.
T
The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls
below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on
the TADJ pin to 625mV at the required temperature threshold. This will give 100% LED current below the threshold
temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the
value of Rth and/or the thermistor to suit the requirements of the chosen LED.
The Thermal Control feature can be disabled by connecting T
Here is a simple procedure to design the thermal feedback circuit:
1. Select the temperature threshold T
2. Select the Thermistor TH1 (both resistive value at 25˚C and beta)
3. Select the value of the resistor R
For example,
ADJ
1)
2)
3)
pin - Thermal control of LED current
Temperature threshold T
TH1 = 10kΩ at 25˚C and beta= 3500
R
TH
= TH1 at T
THRESHOLD
THRESHOLD
= 3.3kΩ
TH
(Continued)
THRESHOLD
as R
Fig 46. Stand-by state from PWM signal
Figure 47. Thermal feedback network
TH
60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST
= 70˚C
= TH1 at T
at which the current must start to decrease
www.diodes.com
TH1 = 3.3kΩ at 70˚C
THRESHOLD
27 of 37
ADJ
LED DRIVER CONVERTER WITH AEC-Q100
to REF.
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A Product Line of
© Diodes Incorporated
ZXLD1374
March 2011