ZXLD1320
Buck mode DC-DC converter for LED driving with
1.5A output and current control
Description
The ZXLD1320 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 1.5A output current.
Applications cover both commercial and
automotive environments with input voltages
ranging from 4V to 18V. Depending upon
supply voltage and external components, this
can provide up to 24W of output power.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and operates in the
step-down (Buck) operating mode, offering
higher power efficiency and lower system
cost than conventional PFM circuitry.
The device includes the DC-DC converter, a
high-side current monitor and an NPN
switching transistor to provide an integrated
solution offering small PCB size, competitive
cost/performance, high power efficiency of
DC-DC conversion and maximum LED
brightness/reliability. More importantly, it
retains design flexibility to add customer
specific features.
The feedback control circuitry inside the
ZXLD1320 provides excellent load and current
regulation, resulting in very stable LED current
over the full operating voltage and temperature
range.
The LED current can be adjusted from 100%
down to 10% of the set value by applying a dc
voltage to the ADJ pin and down to 1% by
applying a PWM signal. An on-chip LED
protection circuit also allows output current to
be reduced linearly above a predetermined
threshold temperature using an external
thermistor at the TADJ pin.
External resistors set nominal average LED
current and coil peak current independently.
The 'Power-OK' (POK) output flag remains high
during normal operation, but switches low if the
switch transistor remains on for more than
500
μ
s. This provides indication of a low battery,
or fault condition. The POK output may be used
to drive an LED or the input of an MCU.
The device can be shut down by applying a
continuous low level dc voltage to the ADJ pin.
Features
•
•
•
•
•
•
•
•
•
•
•
Step-down LED driver
4V to 18V input voltage range
Up to 1.5A output current
Typical efficiency
#
> 85%
User-defined thermal control of LED
output current using external thermistor
High output current stability over input
voltage and temperature
12
μ
A typical standby current
LED current adjustable from 100%
down to 2%
Adjustable soft-start
Power 'OK' flag output
Capable of driving 4 LEDs in series
Applications
•
•
•
•
•
Low voltage halogen lamp replacement
with LEDs
High power LED flashlights
LED back-up lighting
General LED lighting
Automotive lighting
Note* : Using standard external components as specified under electrical characteristics. Efficiency is dependent upon
external component types and values. Higher efficiency is possible with alternative coils.
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ZXLD1320
Pin connections (top-view)
Package view
Package
14-Pin DFN with exposed pad
4mm x 3mm
0.50mm pitch
1.5W @T
A
=70°C
DFN14 Package (bottom view).
45° chamfer denotes Pin 1
Block diagram
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ZXLD1320
Absolute maximum ratings
(Voltages relative to GND unless otherwise stated)
Operating temperature (Top)
Storage temperature (Tst)
Junction temperature (Tj)
Package power dissipation (Ptot)
DFN-14 with Exposed Pad: 4mmx3mm, 0.5mm Pitch
DC-DC Converter
Supply voltage (VIN)
POK
ADJ
CFB
ISENSE
TADJ
BIAS
POK
High-Side current monitor
Continuous sense voltage
(M_VIN – M_LOAD)
Switching NPN transistor
Collector-Base voltage (V
CBO
)
Collector-Emitter voltage (V
CEO
)
Peak pulse current (I
CM
)
Continuous Collector current (I
C
)
20V
20V
3A (Pulse Width = 300µs. Duty Cycle<=2%)
1.5A
-0.3V to +5V
-0.3V to +18V
-0.3V to VIN + 0.3V
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-0.3V to The lower of (+5.0V) or (VIN + 0.3V)
-40 to 125°C
-55 to 150°C
-40 to 150°C
1.5W at Tamb = 70°C
These are stress ratings only. Operation outside the absolute maximum ratings may cause device
failure. Operation at the absolute maximum ratings for extended periods may reduce device
reliability.
Thermal resistance
Junction to ambient (R
JA
)
DFN-14
Nominal value
53°C/W
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ZXLD1320
Pin description
Name
ADJ
Pin Description
#
1
Adjust input
• Leave floating, or connect to VREF to set 100% output current.
• Drive with dc voltage. (50mV<VADJ< VREF) to adjust output current
from 10% to 100% of set value. (DC brightness control mode)
• Drive with low frequency (200Hz) PWM control signal to gate output
‘on’ and ‘off’ at the PWM frequency. (PWM brightness control mode)
• Drive with low level dc voltage (V
ADJ
<28mV) to turn off device
(Standby mode)
Bias pin for setting base current of internal switch transistor
• Short pin to ground to define maximum base drive current for
output switch (Maximum output current condition)
• Connect resistor (R
BIAS
) from this pin to ground to reduce base
drive current (Reduced output current condition)
Control input/output for feedback control loop
• Connect 10nF capacitor from this pin to ground to provide loop
compensation
Power OK flag output
• Pin is high during normal operation.
• Pin switches low if the switch remains on for more than 500µs (nom)
Switch peak current sense pin
• Connect resistor (Rsense) from this pin to ground to define peak
switch current (I
SWPEAK
)=0.05/R
S
Switch emitters (Connect both pins to top of R
SENSE
to sense emitter current)
Switch Collectors (Connect both pins to lower side of coil)
Load side input of high side current monitor.
Connect to sensing resistor RM.
Not connected locally
Positive supply to device (4-18V) and sensing resistor R
M
• Decouple to ground with capacitor close to device
• nominal average output (LED) current = 0.1/R
M
Temperature Adjust input for LED thermal compensation
• Connect thermistor/resistor network to this pin to reduce output
current above a preset temperature threshold.
• Connect to VREF to disable thermal compensation function
(see section on temperature control for details)
Internal 0.5V reference voltage output
Connect to Ground (0V)
BIAS
2
CFB
3
POK
4
ISENSE
5
EMITTER1
EMITTER2
COLLECTOR2
COLLECTOR1
M_LOAD
N/C
VIN
6
7
8
9
10
11
12
TADJ
13
VREF
Exposed Pad
14
15
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ZXLD1320
Electrical characteristics
(
Test conditions: VIN = 4V, T
AMB
= 25°C unless otherwise stated
(a)
)
DC-DC converter supply parameters
Symbol
V
IN
Iq
Parameter
Supply voltage
Quiescent current
Conditions
Normal operation
Measured into VIN
ADJ pin floating.
(Excluding switch
base current).
Measured into VIN.
ADJ pin grounded
ADJ pin floating
2.0V<VIN<18V
480
Min
4.0
1.5
Typ
Max
18
Units
V
mA
I
STBY
V
REF
T
CO(REF)
Standby current
Internal reference voltage
Internal reference temperature
coefficient.
12
500
50
20
520
µA
mV
ppm
/K
NOTES:
(a) Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified from -40°C to
+125° Care guaranteed by design, characterisation and process control.
DC-DC converter input parameters
Symbol
V
SENSE
I
SENSE
Parameter
Peak switch current sense
voltage
Sense input current
Conditions
Measured on I
SENSE
pin CFB pin at 0V
Measured into
ISENSE with pin at
0V.
CFB pin at 0V
Min
45
-15
Typ
55
-7
Max
65
-1
Units
mV
µA
C
FB
V
ADJ
Control loop compensation
capacitor
External dc control voltage
applied to ADJ pin to adjust
output current
DC brightness
control mode
50
10
500
nF
mV
V
ADJ(th)
TCO
(VADJ)
R
ADJ
Switching threshold of ADJ pin Standby state to
normal operation
Temperature coefficient of
VADJ(th)
Internal resistor between VREF VADJ<500mV
and ADJ
26
28
+0.3
100
575
30
mV
%/K
kΩ
mV
VADJ(clmp) Internal clamp voltage on ADJ 100µA injected into
pin
ADJ pin
Issue 1 - January 2008
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NXP MCU
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