350mA LED driver with internal switch

GA1350
40V LED driver with internal switch
Features
General Description
The GA1350 is a continuous mode inductive step-down
converter, designed for driving a single LED or multiple
series connected LEDs efficiently from a voltage source
higher than the LED voltage. The chip operates from an
input supply between 6V and 40V and provides an
externally adjustable output current of up to 750mA.
Depending upon supply voltage and external components,
this can provide up to 30 watts of output power.
The GA1350 includes an integrated output switch and a
high-side output current sensing circuit, which uses an
external resistor to set the nominal average output current.
Output current can be adjusted linearly by applying an
external control signal to the ADJ pin. The ADJ pin will
accept either a DC voltage or a PWM waveform. This will
provide either a continuous or a gated output current.
Applying a voltage of 0.2V or lower to the ADJ pin turns
the output off and switches the chip into a low current
standby state.
The chip is assembled in SOT23-5 and SOT89-5 package.
SOT23-5 is available for 350mA output current application;
SOT89-5 is available for 700mA output current application.
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Simple low parts count
Internal 40V power switch
Wide input voltage range: 6V to 40V
Up to 750mA output current(SOT89-5 package)
High efficiency (up to 95% )
Typical 1200:1 dimming rate
Typical 5% output current accuracy
Single pin on/off and brightness control using DC
voltage or PWM
Up to 1MHz switching frequency
Inherent open-circuit LED protection
Thermal shutdown protection circuitry
Two packages available for different current
Applications
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Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated sign
Application Circuit
April 2009 Ver1.0
1
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Pin Configurations
Package
Pin
SOT23-5
SOT89-5
Configurations
LX
1
5
VIN
GND
2
ADJ
3
4
ISENSE
LX
1
5
VIN
GND
2
ADJ
3
Thermal Pad
4
Isense
Pin Description
Pin Name
NO.
LX
1
Drain of power switch
GND
2
Ground (0V)
ADJ
3
Multi-function On/Off and brightness control pin:
* Leave floating for normal operation.(VADJ = VREF = 1.2V giving nominal average output current
IOUT nom =0.1/RS )
* Drive to voltage below 0.2V to turn off output current
* Drive with DC voltage (0.3V<VADJ <1.2V) to adjust output current from 25% to 100% of IOUTnom
* Drive with PWM signal to adjust output current.
* When driving the ADJ pin above 1.2V, the current will be clamped to 100% brightness
automatically.
ISENSE
4
Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom =0.1/RS
VIN
5
Input voltage (6V to 40V). Decouple to ground with 1μF or higher X7R ceramic capacitor close to
device
April 2009 Ver1.0
Description
2
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Ordering information
Order Number
Quantity per reel
Operating Temperature Range
VSENSE
GA1350IS05E-01
3,000
-40 °C to 85°C
91mV to 101mV
GA1350IS05E-02
3,000
-40 °C to 85°C
99mV to 110mV
GA1350IP05E-01
2,500
-40 °C to 85°C
91mV to 101mV
GA1350IP05E-02
2,500
-40 °C to 85°C
99mV to 110mV
GA1350 ---------
I
S
05
E
- 0X
Bin code
01: bin 1 VSENSE=91mV to 101mV
02: bin 2 VSENSE=99mV to 110mV
Environmental code
E: ROHS
Pin code
05: 5 pin
Package Type
S:SOT23-5
Operating temperature range
I: Industry Standard
GA1350 ----------
I
P
05
E – 0X
Bin code
01: bin VSENSE=91mV to 101mV
02: bin VSENSE=99mV to 110mV
Environmental code
E: ROHS
Pin code
05: 5 pin
Package Type
P:SOT89-5
Operating temperature range
I: Industry Standard
April 2009 Ver1.0
3
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Absolute maximum ratings
Symbol
Parameter
Rating
VIN
Input voltage
-0.3V to +50V
VISENSE
ISENSE voltage
VLX
LX output voltage
-0.3V to +50V
VADJ
Adjust pin input voltage
-0.3V to +6V
ILX
Switch output current
Ptot
Power dissipation
1.2w @SOT89-5;[email protected]
TOP
Operating temperature
-40 to 85°C
TST
Storage temperature
-55 to 150°C
Tj MAX
Junction temperature
150°C
RθJA
Junction to ambient
108°C/W @SOT23-5; 45°C/W @SOT89-5
ESD Susceptibility(human body mode)
2kV
VIN+0.3V to VIN-5V ,VIN>5V
VIN+0.3V to -0.3V,VIN<5V
[email protected];400mA@ SOT23-5
Electrical characteristics (test conditions: VIN=12V, Tamb=25°C unless otherwise stated) (*)
Symbol
VIN
Parameter
Conditions
Min.
Input voltage
Quiescent supply current with output off
ADJ pin grounded
IINQon
Quiescent supply current with output
switching
ADJ pin floating
VSENSE
Mean current sense threshold voltage
40
40
V
60
80
μA
450
600
μA
91
95
101
GA1350-02
99
105
110
mV
Sense threshold hysteresis
±15
ISENSE pin input current
VREF
Internal reference voltage
VADJ
External control voltage range on ADJ pin
for dc brightness control
VADJoff
DC voltage on ADJ pin to switch chip from
active (on) state to quiescent (off) state
VADJ falling
0.15
VADJon
DC voltage on ADJ pin to switch chip from
quiescent (off) state to active (on) state
VADJ rising
0.2
April 2009 Ver1.0
Unit
GA1350-01
ISENSE
RADJ
Max.
6
IINQoff
VSENSEHYS
Typ.
Resistance between ADJ pin and VREF
4
VSENSE = 0.1V
8
Measured on ADJ pin
with pin floating
1.2
0.3
%
10
μA
V
1.2
V
0.2
0.25
V
0.25
0.3
V
500
KΩ
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
ILXmean
SOT23-5 package
0.35
SOT89-5 package
0.65
Continuous LX switch current
A
Electrical characteristics (test conditions: VIN=12V, Tamb=25°C unless otherwise stated) (*) (continued)
Symbol
Parameter
ILX(leak)
LX switch leakage current
RLX
LX Switch „On‟ resistance
Conditions
Min.
Typ.
0.9
Max.
Unit
1
μA
1.5
Ω
DPWM(LF)
Brightness control range at low
frequency PWM signal
PWM frequency =100Hz PWM
amplitude=5V,Vin=15V,
L=27uH, Driving 1 LED
1200:1
DPWM(HF)
Brightness control range at low
frequency PWM signal
PWM frequency =10KHz PWM
amplitude=5V,Vin=15V,
L=27uH, Driving 1 LED
13:1
Operating frequency
ADJ pin floating
L=100μH (0.82Ω) IOUT=350mA
@ VLED=3.4V Driving 1 LED
154
KHz
fLX
TONmin
Minimum switch „ON‟ time
LX switch „ON‟
200
ns
TOFFmin
Minimum switch „OFF‟ time
Recommended
maximum
operating frequency
Recommended duty cycle range
of output switch at fLXmax
Internal comparator propagation
delay
LX switch „OFF‟
200
ns
fLXmax
DLX
TPD
TSD
TSD-HYS
1
0.3
0.7
MHz
0.9
50
ns
Thermal shutdown temperature
140
°C
Thermal shutdown hysteresis
20
°C
NOTES:
(*) Production testing of the chip is performed at 25°C. Functional operation of the chip and parameters specified are guaranteed by design,
characterization and process control in other temperature
April 2009 Ver1.0
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Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Typical operating conditions
For typical application circuit
and
Tamb=25°C unless otherwise stated.
100
6
1LED
4LED
5LED
80
6LED
7LED
70
8LED
9LED
60
10LED
Devilation from nominal
current(%)
Efficiency (%)
3LED
1LED
5
2LED
90
2LED
4
3LED
3
4LED
5LED
2
6LED
1
7LED
8LED
0
9LED
-1
50
5
10
15
20
25
30
35
10LED
-2
40
5
10
15
20
1LED
2LED
Effiency (%)
90
3LED
4LED
80
5LED
6LED
7LED
70
8LED
9LED
60
10LED
50
15
20
25
30
35
40
35
40
7
6
1LED
5
2LED
4
3LED
4LED
3
5LED
2
6LED
1
7LED
0
8LED
-1
9LED
-2
10LED
-3
5
Vin(V)
10
15
20
25
30
35
40
Vin(V)
Output current variation with Supply Voltage
L=47uH, Rs=0.33Ohm
Efficiency vs. No. of LEDs
L=47uH, Rs=0.33Ohm
April 2009 Ver1.0
Devilation from nominal current(%)
100
10
30
Output current variation with Supply Voltage
L=100uH,Rs=0.33Ohm
Efficiency vs. No. of LEDs
L=100uH, Rs=0.33Ohm
5
25
Vin(V)
Vin(V)
6
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Typical operating conditions (continued)
1.4
1.201
1.2
1.2005
Vref(V)
Vref(V)
1
1.2
1.1995
0.8
0.6
0.4
1.199
0.2
0
1.1985
5
10
15
20
25
30
35
0
40
2
4
Vref vs. Vin over nominal supply voltage range
8
10
Vref vs. Vin at low supply voltage
600
120
500
100
400
80
Iin(uA)
Iin(uA)
6
Vin(V)
Vin(V)
300
200
100
60
40
20
0
0
0
5
10
15
20
25
30
35
40
Vin(V)
5
10
15
20
25
30
35
Vin(V)
Supply Current vs. Vin (Operating)
April 2009 Ver1.0
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Shutdown Current vs. Vin (Quiescent)
7
Suzhou Good-Ark Electronics Co., LTd.
40
GA1350
Application notes
Setting nominal average output current with external
resistor R S
The nominal average output current in the LED(s) is
determined by the value of the external current sense
resistor (RS) connected between VIN and ISENSE and in is
given by:
IOUT nom = 0.1/R S [for R S>0.13Ω]
The table below gives values of nominal average output
current for several preferred values of current setting
resistor (RS) in the typical application circuit shown on
page 1:
RS (Ω)
Nominal average
output current (mA)
0.13
769
0.15
667
0.27
370
0.3
333
Vsense is divided into two range to improve current accuracy,
please refer to bin information on page 3.
The above values assume that the ADJ pin is floating and at
a nominal voltage of VREF =1.2V.
Note that RS=0.13Ω is the minimum allowed value of sense
resistor under these conditions to maintain switch current
below the specified maximum value.
40V LED driver with internal switch
VREF. When driving the ADJ pin above 1.2V, the current
will be clamped to 100% brightness automatically.
The input impedance of the ADJ pin is 500kΩ ±25%.
Output current adjustment by PWM control
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle
DPWM can be applied to the ADJ pin, as shown below, to
adjust the output current to a value below the nominal
average value set by resistor RS ,the signal range is from
0V~5V..The PWM signal must have the driving ability to
drive internal 500KΩ pull-up resistor.
Driving the ADJ input from a microcontroller
Another possibility is to drive the chip from the open drain
output of a microcontroller. The diagram below shows one
method of doing this:
It is possible to use different values of RS if the ADJ pin is
driven from an external voltage.
Output current adjustment by external DC control
voltage
The ADJ pin can be driven by an external dc voltage (VADJ),
as shown, to adjust the output current to a value above or
below the nominal average value defined by RS.
The diode and resistor suppress possible high amplitude
negative spikes on the ADJ input resulting from the
drain-source capacitance of the FET. Negative spikes at the
input to the chip should be avoided as they may cause
errors in output current or erratic device operation.
See the section on PWM dimming for more details of the
various modes of control using high frequency and low
frequency PWM signals.
Shutdown mode
The nominal average output current in this case is given by:
IOUTdc = 0.083*VADJ /RS [for 0.3V< VADJ <1.2V]
Note that 100% brightness setting corresponds to VADJ =
April 2009 Ver1.0
8
Taking the ADJ pin to a voltage below 0.2V will turn off
the output and supply current will fall to a low standby
level of 60μA nominal.
Suzhou Good-Ark Electronics Co., LTd.
GA1350
Inherent open-circuit LED protection
If the connection to the LED(s) is open-circuited, the coil is
isolated from the LX pin of the chip, so the chip will not be
damaged, unlike in many boost converters, where the back
EMF may damage the internal switch by forcing the drain
above its breakdown voltage.
Capacitor selection
A low ESR capacitor should be used for input decoupling,
as the ESR of this capacitor appears in series with the
supply source impedance and lowers overall efficiency.
This capacitor has to supply the relatively high peak current
to the coil and smooth the current ripple on the input
supply.
If the source is DC supply ,the capacitor is decided by
ripple of the source, the value is given by:
Cmin 
I F * Ton
U MAX
40V LED driver with internal switch
The chosen coil should have a saturation current higher
than the peak output current and a continuous current rating
above the required mean output current. It is recommended
to use inductor with saturation current bigger than 1.2A for
700mA output current and inductor with saturation current
bigger than 500mA for 350mA output current.
The inductor value should be chosen to maintain
operating duty cycle and switch 'on/off' times within the
specified limits over the supply voltage and load current
range.
The following equations can be used as a guide.
LX Switch 'On' time
TON 
V IN  V LED
LI
 I AVG ( R S  rL  R LX )
Note: TONmin>200ns
LX Switch 'Off' time
IF is the value of output current, U MAX is the ripple of
power supply. Ton is the “ON” time of MOSFET
TOFF 
V LED
LI
 V D  I AVG (rL  R S )
Note: TOFFmin>200ns
the value is normally 2 times of the minimum value.
If the source is an AC supply, typical output voltages
ripple from a nominal 12V AC transformer can be ±10%.If
the input capacitor value is lower than 200μF, the AC input
waveform is distorted, sometimes the lowest value will be
lower than the forward voltage of LED strings. This lower
the average current of the LEDs. So it is recommended to
set the value of the capacitor bigger than 200uF.
Where:
For maximum stability over temperature and voltage,
capacitors with X7R, X5R, or better dielectric are
recommended. Capacitors with Y5V dielectric are not
suitable for decoupling in this application and should not be
used.
VIN is the supply voltage (V)
L is the coil inductance (H)
rL is the coil resistance (Ω)
Iavg is the required LED current (A)
ΔI is the coil peak-peak ripple current (A) {Internally set to
0.3 × Iavg}
VLED is the total LED forward voltage (V)
RLX is the switch resistance (Ω)
Inductor selection
VD is the diode forward voltage at the required load current
(V)
Recommended inductor values for the GA1350 are in the
range 47μH to 220μH.
Example:
Higher values of inductance are recommended at higher
supply voltages and low output current in order to minimize
errors due to switching delays, which result in increased
ripple and lower efficiency. Higher values of inductance
also result in a smaller change in output current over the
supply voltage range. (See graphs). The inductor should be
mounted as close to the chip as possible with low resistance
connections to the LX and VIN pins.
April 2009 Ver1.0
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For VIN=12V, L=47μH, rL=0.64Ω, VLED=3.4V, Iavg
=333mA and VD =0.36V
TON = (47e-6 × 0.105)/(12 - 3.4 - 0.612) = 0.62μs
TOFF = (47e-6 × 0.105)/(3.4 + 0.36 + 0.322)= 1.21μs
This gives an operating frequency of 546kHz and a duty
cycle of 0.34
These and other equations are available as a spreadsheet
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
calculator
website.
of
GA1350(excel
file)from
GOOD-ARK
rise of LED voltage.
Operation at low supply voltage
Optimum performance will be achieved by setting the duty
cycle close to 0.5 at the nominal supply voltage. This helps
to equalize the undershoot and overshoot and improves
temperature stability of the output current.
Diode selection
For maximum efficiency and performance, the rectifier (D1)
should be a fast low capacitance Schottky diode with low
reverse leakage at the maximum operating voltage and
temperature.
If alternative diodes are used, it is important to select parts
with a peak current rating above the peak coil current and a
continuous current rating higher than the maximum output
load current. It is very important to consider the reverse
leakage of the diode when operating above 85°C. Excess
leakage will increase the power dissipation in the device.
The higher forward voltage and overshoot due to reverse
recovery time in silicon diodes will increase the peak
voltage on the LX output. If a silicon diode is used, care
should be taken to ensure that the total voltage appearing on
the LX pin including supply ripple, does not exceed the
specified maximum value.
Reducing output ripple
Peak to peak ripple current in the LED can be reduced, if
required, by shunting a capacitor Cled across the LED(s) as
shown below:
The internal regulator disables the drive to the switch until
the supply has risen above the startup threshold set
internally which makes power MOSFET on-resistance
small enough. Above this threshold, the chip will start to
operate. However, with the supply voltage below the
specified minimum value, the switch duty cycle will be
high and the chip power dissipation will be at a maximum.
Care should be taken to avoid operating the chip under such
conditions in the application, in order to minimize the risk
of exceeding the maximum allowed die temperature. (See
next section on thermal considerations).
Note that when driving loads of two or more LEDs, the
forward drop will normally be sufficient to prevent the chip
from switching below approximately 6V. This will
minimize the risk of damage to the chip.
Thermal considerations
When operating the chip at high ambient temperatures, or
when driving maximum load current, care must be taken to
avoid exceeding the package power dissipation limits. Two
packages are available for different application because of
thermal consideration. SOT23-5 is only available for
350mA current output application. The SOT89-5 package‟s
thermal resistance is much lower so that it can handle
700mA current and suitable for 700mA application.
Note that the chip power dissipation will most often be a
maximum at minimum supply voltage. It will also increase
if the efficiency of the circuit is low. This may result from
the use of unsuitable coils, or excessive parasitic output
capacitance on the switch output.
Layout considerations
LX pin
The LX pin of the chip is a fast switching node, so PCB
traces should be kept as short as possible. To minimize
ground 'bounce', the ground pin of the chip should be
soldered directly to the ground plane.
Coil and decoupling capacitors
A value of 1μF will reduce nominal ripple current by a
factor three (approx.). Proportionally lower ripple can be
achieved with higher capacitor values. Note that the
capacitor will not affect operating frequency or efficiency,
but it will increase start-up delay, by reducing the rate of
April 2009 Ver1.0
10
It is particularly important to mount the coil and the input
decoupling capacitor close to the chip to minimize parasitic
resistance and inductance, which will degrade efficiency. It
is also important to take account of any trace resistance in
series with current sense resistor RS.
ADJ pin
Suzhou Good-Ark Electronics Co., LTd.
GA1350
The ADJ pin is a high impedance input, so when left
floating, PCB traces to this pin should be as short as
possible to reduce noise pickup. ADJ pin can also be
connected to a voltage between 1.2V~5V. In this case, the
internal circuit will clamp the output current at the value
which is set by ADJ=1.2V.
40V LED driver with internal switch
Avoid running any high voltage traces close to the ADJ pin,
to reduce the risk of leakage due to board contamination.
Any such leakage may raise the ADJ pin voltage and cause
excessive output current. A ground ring placed around the
ADJ pin will minimize changes in output current under
these conditions.
High voltage traces
April 2009 Ver1.0
11
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
Package Information
SOT23-5
April 2009 Ver1.0
12
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
SOT89-5
April 2009 Ver1.0
13
Suzhou Good-Ark Electronics Co., LTd.
GA1350
40V LED driver with internal switch
April 2009 Ver1.0
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Suzhou Good-Ark Electronics Co., LTd.