参考資料
SEMICONDUCTOR
CL6807
35V 1A LED driver with internal switch
GENERAL DESCRIPTION
The CL6807 is a continuous mode inductive step-down converter, designed for driving single
or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage.
The device operates from an input supply between 6V and 35V and provides an externally
adjustable output current of up to 1A. Depending upon supply voltage and external components,
this can provide up to 35 watts of output power.
FEATURES
Simple low parts count
Wide input voltage range: 6V to 35V
Up to 1A output current
Single pin on/off and brightness control
using DC voltage or PWM
Typical 5% output current accuracy
Inherent open-circuit LED protection
High efficiency (up to 95%)
High-Side Current Sense
Soft-start
Available in SOT89-5 packages
APPLICATIONS
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
PIN ASSIGNMENT
TYPICAL APPLICATIONS
PIN DESCRIPTIONS
SOP8
1
2 5
PIN NO.
SOT89-5 SOT23-5
1
1
2
2
PIN
NAMES
LX
GND
DESCRIPTION
Drain of the internal N-Ch MOSFET switch.
Ground.
Multi-function On/Off and brightness control pin:
Leave floating for normal operation (V
ADJ
was internal
pulled up) .average output current I
OUTnom
= 0.1/R
S
)
Drive to voltage below 0.4V to turn off output current
Drive with DC voltage (0.5V < VADJ < 2.5V) to adjust
output current from 0% to 100% of IOUTnom
Drive with PWM signal from open-collector or
open-drain transistor, to adjust output current.
Adjustment range 25% to 100% of I
OUTnom
for f>10kHz
and 1% to 100% of I
OUTnom
for f < 500Hz
Connect a capacitor from this pin to ground to
increase soft-start time.
Current sense input
Input Supply Pin. Must be locally bypassed
4
3
5
ADJ
6
8
4
5
4
3
ISNS
VIN
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
IN
SW
ISNS
ADJ
P
DMAX
P
TR
T
J
T
STG
ITEMS
Supply Voltage
Drain of the internal power switch
Current sense input (Respect to VIN)
Logic level dimming input
Power Dissipation (Note 2)
Thermal Resistance, SOT89-5 θJA
Operation Junction Temperature Range
Storage Temperature
ESD Susceptibility (Note 3)
VALUE
-0.3~35
-0.3~35
+0.3~(-5.0)
-0.3~6
Internally Limited
45
-40 to 150
-55 to 150
2
UNIT
V
V
V
V
W
°C /W
°C
°C
kV
RECOMMENDED OPERATING RANGE
SYMBOL
VIN
TOPT
ITEMS
VDD Supply Voltage
Operating Temperature
VALUE
0 ~ 35
-40 to +85
UNIT
V
°C
performance.
Note 2:
The maximum power dissipation must be derated at elevated temperatures and is dictated
by T
JMAX
, θ
JA
,and the ambient temperature T
A
. The maximum allowable power dissipation is P
DMAX
= (T
JMAX
- T
A
)/ θ
JA
or thenumber given in Absolute Maximum Ratings, whichever is lower.
Note 3:
Human body model, 100pF discharged through a 1.5kΩ resistor.
5V Regulator
VCC is the output of a 5V regulator capable of sourcing 10mA. VCC was bypassed to GND with
internal capacitor.
ADJ Input
ELECTRICAL CHARACTERISTICS (Note 4, 5)
The following specifications apply for VIN=24V, TA=25 oC, unless specified otherwise.
Symbol
V
IN
F
SW
V
ISNS
V
ISNS_hys
I
ISNS
I
OFF
I
OP
V
ADJ_H
V
ADJ_L
V
ADJ_DC
f
ADJ
D
PWM_LF
Parameter
Conditions
Input Voltage
Max. Switching Frequency
Mean current sense threshold
V
IN
-V
ISNS
voltage
Sense threshold hysteresis
Optional
ISNS Pin Input Current
Quiescent supply current
output off
Quiescent supply current
output switching
ADJ input voltage High
ADJ input voltage Low
DC brightness control
Max. ADJ Frequency
Duty cycle range of
frequency dimming
Brightness control range
Duty cycle range of
frequency dimming
Brightness control range
ADJ input leakage high
Duty cycle range of
frequencydimming
LX On Resistance
Continuous LX Current
LX Leakage Current
with
with
2.5
0.5
low
f
ADJ
> 100Hz
0.02%
5000:1
high
f
ADJ
< 20KHz
V
ADJ
= 5V
high
V
ADJ
= 0
I
LX
=1A
4%
25:1
-1
0.2
0.5
0.5
1
5
+1
1
Ω
A
μA
uA
1
0.5
2.5
20
1
V
IN
-V
ISNS
=100mV
Min.
6
95
Typ.
Max.
35
1
105
Unit
V
MHz
mV
%
%
μA
μA
mA
V
V
V
kHz
The CL6807 allow dimming with a PWM signal at the ADJ input. A logic level below 0.5V at ADJ
turns off the LED current. To turn the LED current on, the logic level at ADJ must be at least 2.5V.
APPLICATION DESCRIPTION
Selecting R
SENSE
to Set the LED Current
参考資料
100
±15
± 30
8
75
1.8
The CL6807 feature a programmable LED current using a resistor connected between VIN and
ISNS. Use the following equation to calculate the sense resistor:
0 .1
×
V
ADJ
( 0 .5
V
≤
V
ADJ
≤
2 .5
V
)
2 .5
×
Rs
Current Regulator Operation
I
out
=
The CL6807 regulate the LED output current using an input comparator with hysteresis (Figure
1). As the current through the inductor ramps up and the voltage across the sense resistor reaches
the upper threshold, turns off the internal MOSFET. The MOSFET turns on again when the inductor
current ramps down through the freewheeling diode until the voltage across the sense resistor
equals the lower threshold. Use the following equation to determine the operating frequency:
f
sw
=
(
VIN
−
n
×
V
LED
)
×
n
×
V
LED
×
R
SENSE
VIN
× Δ
V
×
L
where n = number of LEDs, V
LED
= forward voltage drop of one LED, and ΔV = (V
SNS_HI
-
V
SNS_LO
).
D
PWM_HF
I
ADJ_H
I
ADJ_L
R
LX
I
LXmean
I
LEAK
Note 4:
Typical parameters are measured at 25°C and represent the parametric norm.
Note 5:
Datasheet min/max specification limits are guaranteed by design, test, or statistical
analysis.
SIMPLIFIED BLOCK DIAGRAM
Figure 1. Current Regulator Operation
VIN
REGULATOR
Freewheeling Diode Selection
The forward voltage of the freewheeling diode should be as low as possible for better efficiency.
A Schottky diode is a good choice as long as the breakdown voltage is high enough to withstand
the maximum operating voltage. The forward current rating of the diode must be at least equal to
the maximum LED current.
-
+
ISNS
BANDGAP
REF
Current Sense
COMPARATOR
1.25V
+
-
UVLO
COMPARATOR
LX
LED Current Ripple
DRIVER
LOGIC
The LED current ripple is equal to the inductor current ripple. In cases when a lower LED current
ripple is needed, a capacitor can be placed across the LED terminals.
PCB Layout Guidelines
GND
ADJ
ADJ
BUFFER
OPERATION DESCRIPTION
The CL6807 are step-down, constant current,high-brightness LED (HB LED) drivers. These
devices operate from a 6V to 35V input voltage range and provide up to 1A souring LEDs. A
highside current-sense resistor sets the output current and a dedicated PWM dimming input (ADJ)
allows for a wide range of independent pulsed dimming. The high-side current-sensing scheme and
on-board current-setting circuitry minimize the number of external components while delivering LED
current with a
5% accuracy below 30V input , using a 1% sense resistor. The device, in
conjunction with the coil (L1) and current sense resistor (RS), forms a self oscillating
continuous-mode buck converter.
When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no
output fromthe current sense circuit. Under this condition, the output of CS comparator is high. This
turns MN on and switches the LX pin low, causing current to flow from VIN to ground, via R
S
, L1 and
the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (V
ISNS
)
across RS. When (V
IN
-V
ISNS
) >115mV, the output of CS comparator switches low and MN turns off.
The current flowing on the RS decreases at another rate. When (V
IN
-V
ISNS
) < 85mV, the MN turns
on again and the mean current on the LED is determined by ((85+ 115)/2
mV)
/
R
S
= 100mV /
R
S
.
The high-side current-sensing scheme and on-boardcurrent-setting circuitry minimize the
number of external components while delivering LED current with ±5% accuracy, using a 1% sense
resistor.
The CL6807 allow dimming with a PWM signal at the ADJ input. A logic level below 0.3V at ADJ
forces CL6807 to turn off the LED and the logic level at ADJ must be at least 2.5V to turn on the
Careful PCB layout is critical to achieve low switching losses and stable operation. Use a
multilayer board whenever possible for better noise immunity. Minimize ground noise by connecting
high-current ground returns, the input bypass-capacitor ground lead, and the output-filter ground
lead to a single point (star ground configuration). In normal operation, there are two power loops.
One is formed when the internal MOSFET is on and the high current flows through IN—RSENSE—
LEDs—Inductor—MOSFET—GND. The other loop is formed when the internal MOSFET is off
when the high current circulates through R
SENSE
—LEDs—Inductor—freewheeling diode. To
minimize noise interaction, each loop area should be as small as possible. Place R
SENSE
as close as
possible to the input filter and VIN. For better noise immunity, a Kelvin connection is strongly
recommended between ISNS and R
SENSE
. Connect the exposed paddle to a large-area ground
plane for improved power dissipation.
PACKAGE INFORMATION
SOT89-5 Package
LED current.
The ADJ pin can be driven by an external dc voltage(V
ADJ
) to adjust the output current to a value
belowthe nominal average value defined by RS.
High luminance LEDs often need to be supplied with atemperature compensated current in
order to maintainstable and reliable operation at all drive levels. The LEDs are usually mounted
remotely from the device so,for this reason, the temperature coefficients of theinternal circuits for
the CL6807 have been optimized tominimize the change in output current when nocompensation is
employed. If output currentcompensation is required, it is possible to use anexternal temperature
sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or
diodes, mounted very close to the LED(s). Theoutput of the sensing network can be used to drive
the ADJ pin in order to reduce output current with increasing temperature.
Symbol
A
b
b1
c
D
D1
E
E1
e
e1
L
Min
1.400
0.320
0.360
0.350
4.400
1.400
2.300
3.940
Millimeters
Max
1.600
0.520
0.560
0.440
4.600
1.800
2.600
4.250
1500 TYP
2.900
0.900
3.100
1.100
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