ZXLD1374_11 DIODES [Diodes Incorporated], ZXLD1374_11 Datasheet - Page 14

• 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 ZXLD1374 is a high accuracy hysteretic inductive Buck/Boost/Buck-boost converter with an internal NMOS switch
designed to be used for current-driving single or multiple series-connected LEDs. The device can be configured to operate
in Buck, Boost, or Buck-boost modes by suitable configuration of the external components as shown in the schematics
shown in the device operation description.
Device Operation
a) Buck mode
The most simple Buck circuit is shown in Figure 26 LED
current control in Buck mode is achieved by sensing the coil
current in the sense resistor Rs, connected between the two
inputs of a current monitor within the control loop block. An
output from the control loop drives the input of a comparator
which drives the gate of the internal NMOS switch transistor.
When the switch is on, current flows from V
coil and switch to ground. This current ramps up until an
upper threshold value is reached. At this point the switch is
turned off and the current flows via Rs, LED, coil and D1
back to V
lower threshold value the switch is turned on again and the
cycle of events repeats, resulting in continuous oscillation.
The average current in the LED and coil is equal to the
average of the maximum and minimum threshold currents.
The ripple current (hysteresis) is equal to the difference
between the thresholds.
The control loop maintains the average LED current at the
set level by adjusting the thresholds continuously to force
the average current in the coil to the value demanded by the
voltage on the ADJ pin. This minimizes variation in output
current with changes in operating conditions.
The control loop also attempts to minimize changes in
switching frequency by varying the level of hysteresis. The
hysteresis has a defined minimum (typ 5%) and a maximum
(typ 20%), the frequency may deviate from nominal in
extreme conditions. Loop compensation is achieved by a
single external capacitor C1, connected between SHP and
SGND.
IN
. When the coil current has ramped down to a
60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST
IN
, via Rs, LED,
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LED DRIVER CONVERTER WITH AEC-Q100
Figure 27. Operating Waveforms (Buck Mode)
Figure 26. Buck Configuration
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ZXLD1374
March 2011