Diodes ZETEX ZXLD1370EV2 User Manual

Issue 2 – July 2010 www.diodes.com

© Diodes Incorporated, 2010

ZXLD1370EV2 BUCK/BOOST LED DRIVER

USER GUIDE

Fig.1 ZXLD1370EV2 Evaluation board connection diagram

8-48V 2A

DC PSU

0-1.5A DC

DVM

BUCK/BOOST

1 - 15 LEDs

1.5A

0V

4.5V

Open Drain output

125mV = 10%

2.5V = 200%

-t°

GND

0 – 4.5V Status steps

Thermal connection

ZXLD1370EV2

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Fig2. Schematic diagram

FLAG

ZXLD1370EV2

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PARTS LIST

Ref Value Package Part Number Manufacturer Contact Details
U1 LED Driver

Controller

TSSOP16L ZXLD1370 Diodes Zetex www.diodes.com

Q1 60V N-ch

MOSFET

DPAK DMN6068LK3 Diodes Zetex www.diodes.com

Q2 Q3 60V General

Purpose
Mosfet

SOT23 2N7002 Diodes www.diodes.com

D1 Freewheeling

diode 3A
100V

PowerDI5 PDS3100 Diodes www.diodes.com

D2 51V 200mW

Zener Diodes

SOD323 BZT52C51 Diodes www.diodes.com

D3 Freewheeling

diode 3A
100V

PowerDI5 PDS3100 Diodes www.diodes.com

Z1 47V 300mW

Zener Diode

SOT23 BZX84C47 Diodes www.diodes.com

L1 33uH 2.3A MS1246-333MLB

NPIS24H330MTRF
744-7715330

Coilcraft
NIC Comps.
Wurth

www.coilcraft.com
www.niccomp.com
www.we-

online.com

C1 100pF 10V 0805 Generic
C2 C5 C8 1uF 100V

X7R

1206 GRM31CR72A105KA01L Murata www.murata.com

C3 C4 C9
C10

2.2uF 100V
X7R

1812 GRM43ER72A225KA01L Murata www.murata.com

C6 C7 Not fitted
C11 10nF 100V

X7R

0805 Generic

R1 R2 0R3 1206 Generic
R4 1K3 0805 Generic
R7 47K 0805 Generic
R9 120K 1% 0805 Generic
R10 36K 1% 0805 Generic
R3 R5 R6
R8 R11
R12 R14

0R 0805 Generic

R15 2K 0805 Generic
R13 R18 Not fitted
R16 R17
R19

1K 0805 Generic

ZXLD1370EV2

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NOTES

The PCB is supplied with R3 and R8 0R0 resistors fitted.
The ‘ADJ’ pin and the ‘TADG’ pin are disabled.
Boost-only mode is selected by changing PL1

In boost mode, the total LED output voltage is <=47V.
The supply voltage for the ZXLD1370EV2 is >=6V, <= (total LED voltage).

In buck-boost operation, the input voltage range is limited by the overvoltage threshold voltage and the
LED voltage. >=6V, <=(47V – VLED).

For other reference designs or further applications information, please refer to the ZXLD1370
datasheet.

Q2 and Z1 protect the circuit from open-circuit LEDs.
The overvoltage threshold of the evaluation board is 47V. (Set by the 47V Zener diode Z1)

The overvoltage threshold can be increased by using a Zener diode with a higher voltage (56V)
Do not use a Zener diode of higher voltage than the MosFet or ZXLD1370.

Boost and Buck-boost modes, average I

LED

= average I

INDUCTOR

x R10/(R9+R10)

OPERATION

In Boost and Buck-boost mode the LED current is sensed by the series resistor (R1 // R2). An output
from the control loop drives the input of a comparator. The comparator drives the gate of the external
NMOS switch transistor via ‘GATE’. When the NMOS switch is on, current flows from VIN, via (R1 //
R2), inductor and switch to ground and increases until a high value is reached. Then, GATE goes low,
the switch turns off and the current flows through (R1 // R2), the inductor, D1 and the LED, to ‘VIN’
(Buck-boost mode), or ‘GND’ (Boost mode). When the inductor current has gone low, ‘GATE’ goes high,
and the cycle of events repeats. The circuit oscillates. The average current in the LEDs 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 average current in the LED is always less than the average
current in the inductor and the ratio between these currents is set by the values of resistors R9 and
R10. The peak current in the LED is equal to the peak current in the inductor. The control loop keeps
the average LED current at the level set by the voltage on the ‘ADJ’ pin. Loop compensation is
achieved by C1.

Bootstrap Circuit

The ZXLD1370 works normally between 8-60V. For input voltages between 6-8V and high switch
currents that require a fully enhanced MOSFET, it is recommended to use the bootstrap network D2­R13 and remove R11.

ZXLD1370EV2

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Fig. 3 Waveforms for Boost and Buck-boost modes

ZXLD1370EV2

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ADJ Terminal (DC output current adjustment)

On the ZXLD1370EV2, the ‘ADJ’ pin R3 connects the internal 1.25V reference (V

REF

) give 100% LED

current.
The ADJ pin can also be driven with an external DC voltage >=125mV and <= 2.5V to adjust the LED

current to >= 10% and <=200% of the nominal value.
To do this, remove R3, fit R5 and apply an external DC voltage between ‘ADJIN’ and ‘GND’
The voltage V

ADJ

can be derived from a resistor-divider connected between ‘REF’ and ‘GND’.

‘ADJ’ has high impedance within its normal operating voltage range. An internal 2.6V clamp protects the
device against excessive input voltage and limits the maximum output current to approximately 4% above
the maximum current set by ‘V

ADJ

‘ if the maximum input voltage is exceeded.

PWM Terminal (PWM output current control/dimming)

The LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the ‘PWM’ pin
to turn the controller on and off. This will produce an average output current proportional to the duty cycle of
the control signal. During PWM operation, the device remains powered up and only the output switch is
switched by the control signal.

The device can be shut down by taking the PWM pin to < 0.4V with a short to 0V or suitable open collector
NPN, or open drain NMOS transistor, for >15ms. In the shutdown state, most of the circuitry inside the
device is off and the quiescent current will be typically 90µA.

TADJ Terminal (Thermal control of LED current)

The ‘Thermal control’ circuit monitors the voltage on the ‘TADJ’ pin and reduces the output current linearly
if the voltage on ‘TADJ’ < 625mV. An NTC thermistor and resistor can be connected to set the voltage on
the ‘TADJ’ pin = 625mV at the required threshold temperature. This will give 100% LED current below the
threshold temperature and <100% above it as shown in the graph. The temperature threshold can be
changed by adjusting the value of Rth and/or the thermistor to suit the LED used.

On the ZXLD1370EV2, Rth is 1K3 (R4). In order to use thermal control, remove R8, fit R6, and fit a 10K
NTC Negative Temperature Coefficient) type thermistor between ‘TADJ’ and ‘GND’. This will set the
threshold temperature to ~ 90ºC.

Thermal control by LED current reduction

Fig. 4 Thermal control

The Thermal Control feature can be disabled by connecting TADJ to REF through the jumper resistor R8.

ZXLD1370EV2

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BOARD LAYOUT

ZXLD1370EV2

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Sales offices

The Americas

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Westlake Village,
CA 91362-3154
Tel: [phone]
Fax: [phone]

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Balanstraße 59,
D-81541 München
Germany
Tel: [phone]
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7F, No. 50,
Min Chuan Road
Hsin-Tien
Taipei, Taiwan
Tel: [phone]
Fax: [phone]

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Rm. 606, No.1158
Changning Road
Shanghai, China
Tel: [phone]
Fax [phone]

Shenzhen

Room A1103-04,
ANLIAN Plaza, #4018
Jintian Road
Futian CBD,
Shenzhen, China
Tel: [phone]
Fax: [phone]

Korea

6 Floor, Changhwa B/D,
1005-5 Yeongtong-dong,
Yeongtong-gu, Suwon-si,
Gyeonggi-do, Korea 443-813
Tel: [phone]
Fax: [phone]

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