ZXLD1374 データシートの表示（PDF） - Diodes Incorporated.

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ZXLD1374

60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100

Diodes Incorporated. 

A Product Line of

Diodes Incorporated

ZXLD1374

Application 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 VIN, via Rs, LED, 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 VIN. When the coil current has

ramped down to a 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.

The control loop sets the duty cycle so that the sense voltage is

VSENSE

=

0.218⎜⎜⎝⎛

V ADJ

VREF

⎟⎟⎠⎞

Therefore,

ILED

=

⎜⎜⎝⎛

0.218

RS

⎟⎟⎠⎞⎜⎜⎝⎛

V ADJ

VREF

⎟⎟⎠⎞

(Buck mode)

Equation 1

If the ADJ pin is connected to the REF pin, this simplifies to

VIN

C1

GND

R1

VAUXVIN ISM

PWM

GI

LX

ADJ ZXLD1374 LX

REF

TADJ

FLAG

STATUS

SHP NC SGNDPGND

C2

100pF

SD1

L1

Figure 26 Buck Configuration

+11V to

15V typ.

GATE

voltage

tOFF

tON

0V

VIN + VF

Q1

Drain

voltage

0V

IPK

Coil &

LED

current

0A

ILED

=

⎜⎜⎝⎛

0.218

RS

⎟⎟⎠⎞

(Buck

mode).

Sense

voltage

VIN - VISM

Mean = 218mV

Figure 27 Operating Waveforms (Buck Mode)

ZXLD1374

Document number: DS35032 Rev. 3 - 2

15 of 39

www.diodes.com

September 2012

© Diodes Incorporated

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