CAT4026 D

CAT4026
6-Channel LED Controller
with Fault Diagnostics for
Large Panel LED
Backlighting
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Description
The CAT4026 is a high performance, large panel LED controller
designed to control six constant current high voltage LED strings.
Added control circuitry monitors the lowest cathode voltage and
generates a feedback control signal to an external Switch Mode Power
Supply (SMPS) to provide a low cost and efficient solution for large
panel high voltage LED backlighting.
Each LED channel current is accurately matched and controlled by
sensing an external resistor in series with a low cost bipolar power
transistor. This allows current and heat dissipation concerns to be
mitigated from the CAT4026 device package.
For added system reliability, both Open−Cathode−Anode (OCA)
and Shorted−Cathode−Anode (SCA) fault detection circuitry has been
included along with independent Fault flag logic outputs for
diagnostic purposes.
LED current dimming in all six channels can be precisely controlled
by either a Pulse Width Modulation signal via the PWM input pin or
by an analog dimming voltage applied at the ANLG pin. In addition
the ANLG pin provides a convenient method for limiting the overall
maximum power dissipation in the event of excessive LED shorting
within any LED string.
The device will automatically enter low current shutdown mode by
taking the PWM pin low for an extended length of time.
SOIC−28
V SUFFIX
CASE 751BM
PIN CONNECTIONS
VDD
PWM
ANLG
BASE1
RSET1
BASE2
RSET2
BASE3
RSET3
OCA
C1
N.C.
VA
N.C.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
(Top View)
Features
•
•
•
•
•
•
•
•
•
•
6 Channel LED Controller
Adaptive Feedback Control to External SMPS for Better Efficiency
PWM and Analog Mode Dimming
Short Cathode−Anode (SCA) Fault Protection
Open Cathode−Anode (OCA) Fault Protection
Over−Voltage Protection
Thermal Shutdown Protection
Automatic Inactivity Power Down Mode
SOIC−28L Package
These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS
Compliant
Typical Applications
GND
SCA
VCS
BASE6
RSET6
BASE5
RSET5
BASE4
RSET4
FLT−OCA
C3
FLT−SCA
IFB
VC
28
27
26
25
24
23
22
21
20
19
18
17
16
15
MARKING DIAGRAM
L3A
CAT4026V
YYWWXXXX
L
= Assembly Location Code
3
= Mark “3” for (lead finish Matte−Tin)
A
= Product Revision: Fixed as “A”
CAT4026V = Specific Device Code
YY
= Production Year (Last Two Digits)
WW
= Production Week (Two Digits)
XXXX
= Last Four Digits of Assembly Lot Number
ORDERING INFORMATION
• LCD−TV LED Backlighting
• LED General Lighting
Device
CAT4026V−T1
(Note 1)
Package
Shipping
SOIC−28
(Pb−Free)
1,000/
Tape & Reel
1. Matte Tin Plated Finish (RoHS−compliant)
© Semiconductor Components Industries, LLC, 2011
May, 2011 − Rev. 5
1
Publication Order Number:
CAT4026/D
CAT4026
LED−LLC VOUT
LLC
Feedback
Circuit
10 k
Current
Feedback
5V
C1
1 nF
HI−SENSE
LO−SENSE
6 Channel Cathode Bus
5V
VDD
VC IFB
SHORT
FLT−SCA
OPEN
FLT−OCA
ANLG
6 Channel Cathode Bus
ZvSCA
Voltage
Feedback
Option
PWM
BAS21LT1
X6−Diodes
1.8 V output (user option)
OCA C1 C3
VA
SCA VCS
X6−Diodes
BAS21LT1
CAT4026
BASE[1:6]
PWM
ANLG
Q1
6
RSET[1:6]
Q6
6−Channels
6
GND
Notes: Q1 to Q6 NPN power transistor MJD340 from ON Semiconductor.
External power−derating circuit not shown.
R1
R6
Figure 1. Typical Application Circuit
Table 1. ABSOLUTE MAXIMUM RATINGS
Rating
Symbol
Value
Unit
Vin
−0.3 to 7
V
PWM
−0.3 to 7 V or (Vin + 0.3),
whichever is lower
V
−0.3 to 7 V or (Vin + 0.3),
whichever is lower
V
TJ(max)
150
°C
Storage Temperature Range
TSTG
−65 to 150
°C
Lead Temperature Soldering
Reflow (SMD Styles Only), Pb−Free Versions (Note 3)
TSLD
260
°C
VDD Voltage Range
PWM, ANLG, FLT−OCA, FLT−SCA Voltage Range
RSET[x], BASE[x]
Maximum Junction Temperature
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
2. This device series incorporates ESD protection and is tested by the following methods:
ESD Human Body Model tested per AEC−Q100−002 (EIA/JESD22−A114)
ESD Machine Model tested per AEC−Q100−003 (EIA/JESD22−A115)
This device meets latchup tests defined by JEDEC Standard JESD78.
3. For information, please refer to our Soldering and Mounting Techniques Reference Manual, SOLDERRM/D.
Table 2. THERMAL CHARACTERISTICS
Rating
Symbol
Value
RθJA
RψJC
79
23
Thermal Characteristics, SOIC−28
Thermal Resistance, Junction−to−Air (Note 4)
Thermal Resistance, Junction−to−Case (Note 4)
Unit
°C/W
4. Values based on copper area of 645 mm2 (or 1 in2) of 1 oz copper thickness and FR4 PCB substrate.
Table 3. OPERATING RANGES
Rating
Symbol
Min
Max
Rating
Input Voltage
Vin
4.5
5.5
V
Ambient Temperature
TA
−40
85
°C
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CAT4026
Table 4. ELECTRICAL CHARACTERISTICS (VDD = 5 V, VPWM = VDD, VANLG = 3.3 V, for typical values TA = 25°C, for min/max
values TA = −40°C to +85°C; unless otherwise noted.)
Test Conditions
Parameter
RSET[x] pin voltage
RSET channel to channel voltage matching (VRSET – VRSETAVR) / VRSETAVR ,
Nominal current 100 mA per channel
RSET device to device matching
Symbol
Min
Typ
Max
Unit
VRSET
0.97
1.00
1.03
V
±0.6
±2.0
%
±2.5
VRSET−MA
T
VRSET−D
±0.6
IFB sink current
VVCS = 3.6 V
IIFB
0.5
mA
%
VA output voltage
VA pin no load
VVA
1.8
V
VA output resistance
100 mA load
RVA
250
W
VC output voltage
VC pin no load, VCS pin = 3.6 V
VVC
1.8
V
VC output resistance
100 mA load
RVC
360
W
VCS pull−up resistance to VDD
VPWM = 5 V
RVCS
50
kW
SHUTDOWN, DISABLE, QUIESCENT CURRENTS
Shutdown Current
Shutdown mode (PWM low for > 50 ms)
IOFF
−
50
mA
Disable Current
VPWM = 0 V, all channels off
(PWM low for < 20 ms)
IDIS
−
1.5
mA
Quiescent Current (Note 5)
VPWM = 5 V, R1 to R6 = 10 W (100 mA load
per channel), application circuit as shown with
0.8 mA BASE pin current per channel
IQ
−
16
mA
7.6
mA
mA
No external circuit components present, all
BASE[x] and RSET[x] pins floating
Short Circuit Supply Current
VVCS = GND, all BASE[x] shorted to Ground
IQ−MAX
−
118
VPWM = 5 V
RPWM
80
120
200
VPWM−VIH
VPWM−VIL
−
−
1.2
1.0
−
−
RANLG
120
150
180
LOGIC I/OS
PWM pull−down resistance
PWM Input Threshold Voltage
VIH Logic High
VIL Logic low
V
ANLG divider network pull−down resistance
ANLG to RSET pin voltage ratio
(VANLG / VRSET)
kW
VANLG ≤ 3.0 V, all outputs on, R1−R6 = 10 W
VANLG
/VRSET
3
kW
−
OPEN CATHODE−ANODE FAULT DIAGNOSTICS
VOCA
OCA open−LED threshold voltage
0.97
1.00
1.03
V
FLT−OCA pin pull−down voltage
Open Cathode Anode fault is active,
5 mA sink current
VFLT−OCA
65
mV
FLT−OCA open−drain leakage
Open Cathode Anode fault is inactive
IFLT−OCA
0.2
mA
FLT−OCA fault delay
Delay between OCA fault and FLT−OCA active
TFLT−OCA
1
ms
ISCA−ON
1.3
mA
SHORT CATHODE−ANODE FAULT DIAGNOSTICS
SCA fault detection threshold sink current
FLT−SCA transitions to active state (low)
SCA fault cleared threshold sink current
FLT−SCA transitions to inactive state (high)
ISCA−OFF
0.4
mA
FLT−SCA pin pull−down voltage
Short Cathode Anode fault is active,
5 mA sink current
VFLT−SCA
65
mV
FLT−SCA fault delay
Delay between SCA fault and FLT−SCA active
TFLT−SCA
35
ms
FLT−SCA open−drain leakage
Short Cathode Anode fault is inactive
IFLT−SCA
0.2
mA
5. The quiescent current depends on the external bipolar transistors used (ON Semiconductor MJD340) and more specifically of its DC current gain (hFE).
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CAT4026
Table 4. ELECTRICAL CHARACTERISTICS (VDD = 5 V, VPWM = VDD, VANLG = 3.3 V, for typical values TA = 25°C, for min/max
values TA = −40°C to +85°C; unless otherwise noted.) (continued)
Parameter
Test Conditions
Symbol
Min
Typ
Max
Unit
TIMING
PWM Enable Time
VPWM = 0 V to VDD
Iout = 0 mA to 90% of Iout(nom)
tEN
800
ns
PWM Disable Time
VPWM = VDD to 0 V
Iout = Iout(nom) to 10% of Iout(nom)
tDIS
1
ms
Turn−off Shutdown Time,
PWM falling to shutdown
VPWM = 5 V to 0 V
Iout = Iout(nom) to shutdown mode
tOFF
25
ms
tCC
50
ns
Channel to channel turn on and turn off
delay (staggering)
THERMAL SHUTDOWN
Thermal Shutdown Temperature
TSD
−
150
−
°C
Thermal Shutdown Hysteresis
TSH
−
20
−
°C
Toff
SHUTDOWN
LOGIC IS
RESET
PWM
SHUTDOWN
Tdis
Ten
90%
LED CURRENT
SHUTDOWN 0 mA
ILED = 1 V / RSET
10%
0 mA
VDD QUIESCENT
CURRENT
SHUTDOWN
0 mA
SHUTDOWN 0 mA
Figure 2. Timing Diagram
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CAT4026
TYPICAL PERFORMANCE CHARACTERISTICS
(VDD = VPWM = 5 V, VANLG = 3.3 V, TAMB = 25°C unless otherwise specified.)
1.4
16
PWM VOLTAGE (V)
QUIESCENT CURRENT (mA)
VIH
1.2
1.0
VIL
0.8
0.6
0.4
0.2
0
−40
−10
20
50
80
110
125°C
80°C
4
4.50
4.75
5.00
5.25
5.50
Figure 3. PWM Threshold Voltage vs.
Temperature
Figure 4. Quiescent Current vs. Temperature
1.02
RSETX = 1 kW
1.01
0.8
RSET VOLTAGE (V)
IFB DRIVE CURRENT (mA)
8
VDD VOLTAGE (V)
0.7
0.6
0.5
0.4
0.3
0.2
1.00
0.99
0.98
0.97
0.96
2.0
2.5
3.0
3.5
4.0
0.95
−40
4.5
−10
20
50
80
110
VCS VOLTAGE (V)
TEMPERATURE (°C)
Figure 5. IFB Sink Current vs. VCS Voltage
Figure 6. RSET Voltage vs. Temperature
120
140
1.0
0.8
100
80
MATCHING (%)
LED BRIGHTNESS (%)
−40°C
TEMPERATURE (°C)
0.9
60
40
20
0
25°C
0
140
1.1
1.0
0.1
0
12
0
1
2
3
0.6
Ch2
0.4
Ch6
0.2
Ch4
0
−0.2
Ch5
−0.4
Ch1
−0.6
Ch3
−0.8
−1.0
4
3
6
9
12
15
18
ANLG VOLTAGE (V)
CATHODE VOLTAGE (V)
Figure 7. LED Brightness vs. ANLG Voltage
Figure 8. Matching Channel−to−Channel vs.
Cathode Voltage
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21
CAT4026
TYPICAL PERFORMANCE CHARACTERISTICS
(VDD = VPWM = 5 V, VANLG = 3.3 V, TAMB = 25°C unless otherwise specified.)
30
OCA VOLTAGE (V)
0.99
SHUTDOWN TIME (ms)
1.00
25°C
−40°C
0.98
80°C
0.97
125°C
0.96
0.95
4.50
4.75
5.00
5.25
29
28
25°C
27
80°C
125°C
26
25
5.50
−40°C
4.50
4.75
5.00
5.25
5.50
VDD VOLTAGE (V)
VDD VOLTAGE (V)
Figure 9. OCA Threshold Voltage vs.
Temperature
Figure 10. Shutdown Time vs. Temperature
110
100
90
Dropout
LED BRIGHTNESS (%)
QUIESCENT CURRENT (mA)
100
80
70
60
50
40
30
Normal
Regulation
20
10
0
4.50
4.75
5.00
5.25
80
60
40
20
0
5.50
0
20
40
60
80
VDD VOLTAGE (V)
PWM DUTY CYCLE (%)
Figure 11. Quiescent Current vs. Supply
Voltage (Note 6)
Figure 12. LED Brightness vs. PWM Duty
Cycle
100
6. At initial power up, the CAT4026 will draw a higher quiescent current equal to the “dropout” current until it reaches normal regulation.
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CAT4026
TYPICAL PERFORMANCE CHARACTERISTICS
(VDD = VPWM = 5 V, VANLG = 3.3 V, TAMB = 25°C unless otherwise specified.)
Figure 13. LED Current Transient During PWM
Dimming
Figure 14. ANLG Transient, 20% to 80%
Brightness
Figure 15. Open Cathode−Anode Waveform
Figure 16. Short Cathode−Anode Waveform
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CAT4026
Table 5. PIN DESCRIPTION
Pin #
Name
Function
1
VDD
Supply Bias voltage input for controller
2
PWM
Digital PWM input control to globally PWM all channels
3
ANLG
ANLG input bias signal to globally adjust full scale brightness. (intended for external power derating circuit for SCA conditions)
4, 6, 8, 21,
23, 25
BASE [1:6]
Base drive connection for external channel high voltage BJT
5, 7, 9, 20,
22, 24
RSET [1:6]
Current setting resistor for LED channel (Full Scale Brightness of 1 V)
10
OCA
11
C1
12
N.C.
13
VA
14
N.C.
15
VC
Cathode voltage with compensation (divided by 2 and buffered). Leave floating if not used.
16
IFB
Current sink feedback (1 mA max) used with external circuit to control of LED Anode supply voltage
17
FLT−SCA
18
C3
19
FLT−OCA
26
VCS
Lowest LED Cathode sense input (connect to sensing diode anodes)
27
SCA
Highest LED Cathode sense input (connect to external high voltage transistor and zener/diode network)
28
GND
Ground reference for all pins
Open Cathode Anode over−voltage threshold trigger input (sets maximum allowed LED Anode voltage,
1 V trigger)
LED Anode capacitor
Do not connect, leave floating
Internal cathode reference voltage (divided by 2 and buffered to 1.8 V). Intended to provide reference
bias for external circuitry, such as the power derating operational amplifier.
Do not connect, leave floating
Shorted Cathode−Anode Fault output logic signal (open−drain, active low) indicating presence of excessive cathode voltage
Connect pin to GND
Open Cathode−Anode Fault output logic signal (open−drain, active low) indicating an Open−channel
condition
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CAT4026
Pin Functions
VDD
The VDD input is the positive supply to the devices. VDD
should be nominally 5 V.
Each RSET pin contains internal compensating circuitry
to eliminate the operating base current, thereby maintaining
extremely accurate LED matching on all channels.
PWM
FLT−OCA
The PWM control input provides multiple functions.
When the first rising edge is applied to PWM input, the
CAT4026 will immediately power−up and remain powered
up until the PWM input has been held low for at least
typically 25 ms, at which point the device will enter full
shutdown mode and draw zero current.
When PWM is active (high level), all LED channels are
enabled. When PWM is inactive (low level), all LED
channels are disabled. For PWM dimming frequencies in the
300 Hz range, duty cycles as low as 0.1% are supported.
An internal pull−down resistor (120 kW typical) exists on
the PWM input. PWM logic high and low detection levels
are typically set at 1.2 V and 1.0 V respectively.
The FLT−OCA flag output is active low (open−drain) and
is latched whenever an Open Cathode−Anode fault
condition has been detected on any LED string. An external
pull−up resistor (10 kW) should be connected to FLT−OCA.
For systems requiring complete shutdown upon detection
of any open−LED channel, the FLT−OCA output can be
used to drive the shutdown control of the LED power supply.
For systems which must continue operation under
open−LED channels, the FLT−OCA should only be used for
diagnostic purposes (not for system shutdown).
The FLT−OCA is cleared upon power−down of the
CAT4026 device.
FLT−SCA
ANLG
The FLT−SCA flag output is active low (open−drain) and
becomes active whenever any LED cathode terminal
exceeds a user programmed voltage level (at the SCA pin,
set by an external zener diode). An external pull−up resistor
(10 kW) should be connected to the FLT−SCA pin.
For systems requiring complete shutdown upon detection
of any faulty LED channel, the FLT−SCA output can be used
to drive the shutdown control of the LED power supply.
For systems which must continue operation under faulty
LED channels, the FLT−SCA should only be used for
diagnostic purposes (not for system shutdown). In this case,
the FLT−SCA flag can be used to trigger an external power
derating circuit reducing the applied voltage at the ANLG
control input, thereby reducing the power dissipated in the
external bipolar channel transistors.
Note: If an Open−LED channel is present, the FLT−SCA
flag may become temporary active (depending on the user
threshold levels) while the system is diagnosing the
Open−channel fault. When the system has eventually
cleared (disabled) the open−channel, the fault FLT−SCA
will automatically clear itself once the system has stabilized
and returned back to normal operating conditions.
The ANLG controlled input allows the full scale
brightness level of all channels to be globally reduced. When
the ANLG control is taken below 3 V, the maximum LED
brightness will be equal to 1/3 of the ANLG pin voltage. If
the ANLG pin is taken above 3 V, it will have no further
effect and the brightness will remain at the full scale (100%)
setting.
An internal resistive network to ground (150 kW typical)
exists on the ANLG pin. The external source resistance
driving this input should be taken into consideration when
controlling the ANLG input.
A simple power derating external circuit can be applied to
the ANLG pin whenever excessive voltage is present on any
LED cathode.
If the ANLG control function is not required, the pin
should be pulled high (above 3 V) to ensure full scale
brightness is maintained.
BASE[1:6]
The BASE output pin drives the base of the external NPNs
to regulate the LED current in the associated string to the
preset value. External high−voltage bipolar junction
transistors, such as MJD340, are recommended.
Operating base currents up to 5 mA can be powered from
each of the BASE pins in normal operating conditions. In the
event of any BASE pin being shorted directly to GND,
internal protection circuitry will limit the drive current to
15 mA (typically).
IFB
The IFB pin is a pull−down current sink with a drive level
determined by the lowest LED cathode voltage as shown
below.
RSET[1:6]
The RSET input pins sense the voltage of the external
LED current bias resistors. Each RSET pin is accurately
regulated to a voltage of 1.0 V under the full scale brightness
condition (ANLG > 3.0 V).
VCS Voltage
IFB Drive Current (typ)
> 4.1 V
0 mA
3.3 V
0.5 mA
< 3.1 V
1.0 mA
VCS = Vcathode + Vdiode
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CAT4026
External adjustment of LED Anode supply voltage is
controlled by the IFB current sink in conjunction with an
external feedback circuit. The external circuit should be
configured so that 1 mA drive signal will achieve the desired
necessary dynamic adjustment range for expected worst
case maximum LED string operating voltage range
A linear transconductance relationship exists for the drive
current (1 mA/V) for Cathode operation between 2.5 V and
3.5 V.
If the open−LED function is not used, the OCA pin should
be tied to GND.
VCS
The VCS pin is connected to each LED cathode via a
diode array. This pin detects the lowest LED cathode voltage
and sets the feedback signaling to allow the SMPS to adjust
the LED Anode voltage to the appropriate levels for
optimum efficiency (3 V operating point for the minimum
cathode voltage on any string). An external high voltage
diode array such as BAS21LT is recommended.
C1
Connect a capacitor of 1 nF and a 10 kW resistor from the
C1 pin to the LED Anode voltage. Capacitor voltage rating
must be greater than the highest LED anode voltage.
VA
The VA output pin is optional and allows the user to power
an external feedback control circuit for setting the common
LED Anode operating voltage level.
This output is a buffered voltage signal, which tracks 50%
of the internal reference being used to control and set the
nominal operating level of the lowest LED Cathode string
voltage. An internal source impedance of 250 W is present
on this output and the nominal voltage is set to 1.8 V
(thermal compensation exists to cancel out the external
sensing diode temperature coefficient present on the VCS
pin).
C3
Connect pin to GND.
SCA
The SCA pin is used to detect a severe mismatch in LED
string voltage, such as the occurrence of an Anode−Cathode
short. The SCA pin is connected to each LED cathode via a
diode array and a voltage level translator. The threshold
voltage of the detector can be adjusted by using an external
Zener diode.
A conduction level of 1.5 mA into the SCA pin will trigger
a FAULT condition. The FAULT condition will be cleared
upon the conduction current level falling below 0.5 mA and
normal operation will resume.
VC
The VC pin is a buffered voltage signal, which tracks 50%
of the voltage level present at the VCS input pin (i.e. the VC
voltage is determined by the lowest operating Cathode
voltage present on any LED string).
This signal provides a convenient feedback control
method for systems which use standalone converters to
generate the LED Anode supply voltage (as opposed to a
current feedback option). An external suitable resistive
divider, at the VC pin, can be used to directly control the
feedback input of the standalone converter.
During shutdown mode, the VC pin is forced into high
impedance mode, while during normal operation an output
source impedance of 360 W is present on the VC pin.
OCA
The OCA input is used to detect and protect against
abnormally high LED Anode condition. An external
resistive divider connected to the OCA pin, from the LED
Anode voltage, will trigger a FLT−OCA condition once the
OCA input level exceeds 1.0 V. Any open−LED channel will
automatically be disabled and removed from the feedback
loop when OCA is triggered. This method provides an
auto−recovery feature for the system to resume normal
operation ensuring only the ‘good’ LED channels are
included in the feedback loop.
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CAT4026
Simplified Block Diagram
CH[1:6]
ANLG
−
100 k
CH−BIAS
+
(1 V−CLAMP)
+
15 mA−max
BASE[1:6]
−
50 k
RSET[1:6]
SHUTDOWN
TIMER
ENABLE
LATCHED
NOT−LATCHED
PWM
SHORT
DETECT
SCA
FLT−SCA
CH−PWM
FAULT
DETECT
OPEN
SHORT
+
OCA
FLT−OCA
−
1 mA_max
−
1V
IFB1
+
1 mA/V
4.1 V
+
−
500 mV
C3
3.6 V
VCS
CATHODE
DETECT
C1
5V
0.5X
1.8 V−nom
0.6 V
3V
VDD
Ref
GND
Figure 17. Simplified Block Diagram
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VA
VC
3.6 V−nom
CH−PWM
1.8 V
0.5X
CAT4026
APPLICATION INFORMATION
Shorted LED
In some cases, the LED string voltage may be different
between different strings (channel voltage mismatch). This
can be due to LED forward voltage variation or some LEDs
becoming shorted in one of the string. One of the string
would have a total LED forward voltage lower than other
channels. In operation, the cathode voltage of the “shorted”
channel will be higher than the other channels causing more
power to be dissipated in the external transistor of that
channel. Therefore, it is useful to detect this condition and,
if needed, derate the LED channel current. The highest
cathode voltage is sensed at the SCA pin through a
diode−OR network. A zener in series with the diodes, shown
in Figure 21, allows to adjust the cathode threshold voltage.
Once the SCA pin sinks more than about 1.3 mA, the
FLT−SCA fault is triggered and the pin is pulled low.
Figure 20 shows a power−up waveform for a threshold
voltage at about 45 V. In this example, when the fault is
triggered, the LED current decreases from 100 mA to 20 mA.
Operation with Open and Shorted LED
The CAT4026 can detect both open and shorted LED
strings through two diode−OR circuits connected
respectively to the VCS and SCA pins, as shown in the
application circuit in Figure 1.
Open LED
When one of the channel becomes open or disconnected,
its cathode voltage drops to zero pulled down by the current
sensing resistor (R1−R6). The lowest cathode voltage is
sensed through a diode at the VCS pin (VCS pin is around
0.6 V above the lowest cathode voltage). This causes the
CAT4026 current feedback pin (IFB) current to increase to
1 mA and the power supply to increase the anode voltage
VOUT until the OCA pin exceeds 1 V threshold and latches
on the FLT−OCA fault (the pin is pulled low). At that time,
the CAT4026 disables the open channel (corresponding
BASE pin voltage goes to GND) and will ignore that channel
until the driver is shutdown. The FLT−OCA pin remains low
until the CAT4026 goes to shutdown mode or is powered
down. The output voltage VOUT now returns to normal
operation level where the lowest cathode voltage is around
3.2 V (VCS pin around 3.6 V). The anode voltage is sensed
at the OCA pin through a resistor divider (Ra, Rb) as shown
in Figure 21.
Figure 20. Shorted LED Channel at Power−up
Figure 21 shows a partial application schematic relative to
the OCA and SCA fault detection.
Figure 18. Open LED at Power−up
Figure 21. Schematic for Open/Short Detection
Unused LED Channels
For applications that require less than 6 LED channels, the
unused channel BASE and RSET pins should be left
floating. All the other used channels will operate normally.
Figure 19. Open LED at Power−up, Base Voltages
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12
CAT4026
PACKAGE DIMENSIONS
SOIC−28, 300 mils
CASE 751BM−01
ISSUE O
SYMBOL
MIN
A
2.35
2.65
A1
0.10
0.30
A2
2.05
2.55
b
0.31
0.51
c
0.20
0.33
D
17.78
18.03
E
10.11
10.51
E1
7.34
7.60
E
NOM
e
b
e
PIN #1
IDENTIFICATION
MAX
1.27 BSC
h
0.25
0.75
L
0.40
1.27
θ
0º
8º
θ1
5º
15º
TOP VIEW
h
D
A2 A
A1
h
q1
q
q1 c
L
E1
SIDE VIEW
END VIEW
Notes:
(1) All dimensions are in millimeters. Angles in degrees.
(2) Complies with JEDEC MS-013.
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13
CAT4026
Example of Ordering Information (Note 9)
Prefix
Device #
Suffix
CAT
4026
V
−
T1
Company ID
(Optional)
Product Number
4026
Package
V: SOIC−28L
Lead Finish
Blank: Matte Tin
Tape & Reel (Note 11)
T: Tape & Reel
1: 1,000 / Reel
7. All packages are RoHS−compliant (Lead−free, Halogen−free).
8. The standard lead finish is Matte Tin.
9. The device used in the above example is a CAT4026V−T1 (SOIC−28L, Matte Tin, Tape & Reel, 1,000/Reel).
10. For additional package and temperature options, please contact your nearest ON Semiconductor Sales office.
11. For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: [email protected]
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5773−3850
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14
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
CAT4026/D
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