Download FAN5640 — Dual High-Side Constant Current Source

FAN5640 — Dual High-Side Constant Current Source
for High-Voltage Keypad LED Illumination
Features
Description
 20V Maximum Driver Input Level
 Dual Output
 25mA Drive Capability per Channel
 Two Strings of 2-4 LEDs Each
 External Resistor Sets Maximum Current
 Fast Turn-On/Off Capability
 Low Bias Current
 SC70-6 Package
 Thermal Shutdown Protection
The FAN5640 is designed to illuminate one or two strings
of keypad LEDs with constant high-side current sources.
The device can drive up to four white LEDs in series at a
maximum current of 25mA per channel. If the second
channel is not needed, the channels can be tied
together to boost output current up to 50mA.
An external resistor programs the maximum output
current. Dimming can be accomplished by pulse width
modulation of the enable pin or the input supply rail.
Applications
 Keypad Illumination
 Main Display and Sub-Display Illumination
 Cell Phones, Smart Phones
 Pocket PCs
 PDA, DSC, PMP, and MP3 Players
Figure 1. Typical Application
Ordering Information
Part Number
Operating Temperature Range
Package
Packing Method
FAN5640S7X
-40°C to 85°C
SC70-6 2x2.2mm
Tape and Reel
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
March 2012
1:275 Current
Mirror Ratio
VIN
OTP
+
CLIM
IOUT1
EN
500k
IOUT2
Reference
+
Control
+
-
GND
RSET
Figure 2. Block Diagram
Pin Configuration
Figure 3. Pin Assignments
Pin Definitions
Pin #
Name
Description
Output Current 1. The programmed current IOUT is sourced from this pin. If only one channel is
used, IOUT1 and IOUT2 can be tied together to boost the output current. It can also be left
floating or tied to pin 5.
1
IOUT1
2
GND
Ground
3
RSET
RSET. Connect a programming resistor REXT to this pin. This pin’s output voltage is 0.475V when
EN is HIGH. The current through the external resistor establishes the current IOUT, where IOUT =
275 • [0.475V / REXT].
4
EN
Enable. When HIGH, the IC applies the programmed current IOUT to both IOUT1 and IOUT2.
When LOW, IC enters Shutdown Mode. If pulsed, this pin modulates the output current. The
minimum pulse width is determined by the speed of the turn-on circuitry. This pin contains an
internal pull-down resistor of 500K.
5
VIN
Input Supply. Apply 6 to 20V at this pin (see Dropout Limitations under the Application
Information section).
6
IOUT2
Output Current 2. The programmed current IOUT is sourced from this pin. If only one channel is
used, IOUT1 and IOUT2 can be tied together to boost the output current. It can also be left
floating or tied to pin 5.
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
2
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Block Diagram
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Symbol
VEN
IRSET
Parameter
Min.
Max.
Unit
Enable Voltage
-0.3
6.0
V
VIN, VIOUT1, VIOUT2
-0.3
22.0
V
120
A
Current Sourced by RSET
TJ
Junction Temperature
-40
150
°C
TSTG
Storage Temperature
-65
150
°C
260
°C
TL
ESD
Lead Soldering Temperature, 10 Seconds
Electrostatic Discharge Protection Level
Human Body Model
2
Charged Device Model
2
kV
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to absolute maximum ratings.
Symbol
Parameter
VIN
Supply Voltage
VEN
Enable Voltage
IOUT1, IOUT2
TA
TJ
Min.
Typ.
6
Output Current Range Through Each String
Max.
Unit
20
V
5.5
V
2.5
25.0
mA
(1)
-40
+85
°C
(1)
-40
+125
°C
Max.
Unit
Operating Ambient Temperature Range
Operating Junction Temperature Range
Thermal Properties
Symbol
ΘJA
Parameter
Min.
(1)
Junction to Ambient Thermal Resistance
Typ.
300
°C/W
Note:
1. Junction-to-Ambient thermal resistance is a function of application and board layout. This data is measured with
four-layer, 1s2p boards in accordance with JESD51- JEDEC standard. Special attention must be paid not to
exceed the maximum junction temperature.
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
3
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Absolute Maximum Ratings
VIN = 6V to 20V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C, VIN = 14V, ILED = 15mA.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
20
V
Power Supplies
VIN
Input Voltage Range
IQ
Quiescent Current
ISD
Shutdown Supply Current
VEN
IEN
6
Measured at GND pin, VIN = 20V
48
65
Measured at GND pin, VIN = 6V
44
55
VIN = 20V, EN = GND
8
13
VIN = 6V, EN = GND
5
8
Enable High-Level Input Voltage
1.2
Enable Low-Level Input Voltage
Enable Input Current
0.4
EN = 5V
9
15
EN=GND
0.1
1.0
µA
µA
V
µA
Regulation
ILIM1
Channel 1 Current Limit(2)
ILIM2
(2)
30
Channel 2 Current Limit
30
-15
+15
5mA < IOUT ≤ 25mA(3)
-10
+10
-3
+3
Output Current Accuracy
IMATCH
Channel-to-Channel Current Matching(4)
Output Dropout Voltage
VREF
Reference Voltage
IMIRROR
Current Mirror Ratio
∆IOUT/∆VIN
VIN – VOUT at 90% IOUT
Programmed IOUT = 25mA
1.80
2.50
VIN – VOUT at 90% IOUT
Programmed IOUT = 2.5mA
0.43
0.60
IOUT / IRSET
TSD
Thermal Shutdown Protection
%
mV
275
Power Supply Current Dependency VOUT = VIN – 2V
Turn-On Time
%
V
475
(5)
TON
mA
2.5mA < IOUT ≤ 5mA(3)
∆IOUT
VDO
mA
VIN=14V , IOUT=12.5mA(6)
0.5
2.0
%/V
5
8
µs
Rising Temperature
150
Hysteresis
20
°C
Notes:
2. If only one channel is needed, IOUT1 can be tied to IOUT2 to boost maximum current to 50mA.
3. REXT resistor tolerance adds to the specification limit of the pin RSET to determine overall current accuracy.
4. Matching defined as [(IOUT1-IOUT2)/(IOUT1+IOUT2)]×100.
5. VOUT is the total voltage drop across the LED string.
6. Measured from EN crossing 1.8V to output current reaching 90% of target IOUT.
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
4
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Electrical Characteristics
Unless otherwise noted, CIN = 4.7µF, VEN=1.8V, TA = 25°C, white LED with VF=3.3V at IOUT=10mA.
474.3
REXT = 500K
Quiescent Current (µA)
47.5
+25°C
Voltage at RSET Pin (mV)
48.0
47.0
46.5
+85°C
46.0
45.5
-40°C
45.0
44.5
44.0
43.5
43.0
6
8
10
12
14
16
18
20
REXT = 500K
474.2
474.1
474.0
473.9
473.8
473.7
6
8
10
Input Voltage (V)
Figure 4. Quiescent Current vs. Input Voltage
VEN = 0V
-40°C
7
6
+25°C
4
20
22
8
6
4
2
0
6
8
10
12
14
16
18
20
0
1
2
3
4
5
Input Voltage (V)
Enable Voltage (V)
Figure 6. Shutdown Current vs. Input Voltage
Figure 7. Enable Input Current vs. Enable Voltage
2.0
1.8
2.5
1.6
2.0
Dropout Voltage (V)
Dropout Voltage (V)
18
10
8
5
16
12
+85°C
9
14
Figure 5. RSET Voltage vs. Input Voltage
Enable Current (µA)
Shutdown Current (µA)
10
12
Input Voltage (V)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.5
5.5
10.5
15.5
20.5
LED Current (mA)
1.0
0.5
IOUT=2.5mA
-20
0
20
40
60
80
Temperature (°C)
Figure 8. Dropout Voltage vs. LED Current
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
1.5
0.0
-40
25.5
IOUT=25mA
Figure 9. Dropout Voltage vs. Temperature
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5
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Typical Characteristics
1
VOUT=13V
4 LEDs
0
IOUT=2.5mA
Variation of IOUT Current (%)
Variation of IOUT Current (%)
Unless otherwise noted, CIN = 4.7µF, VEN=1.8V, TA = 25°C, white LED with VF=3.3V at IOUT=10mA.
VOUT=11V
-1
-2
IOUT=25mA
-3
Approaching
Dropout Region
-4
-5
12
13
14
15
16
17
18
19
0.18
VIN=18V
0.12
0.09
IOUT=25mA
0.06
0.03
0
5
20
Current Mirror Ratio
1
1
10
100
282
281
2 LEDs
280
2 LEDs
279
278
277
4 LEDs
276
275
1000
0
5
IOUT Current (mA)
IOUT=2.5mA
3.0
30
2.5
25
2.0
20
IOUT=25mA
15
1.5
10
1.0
5
0.5
0.3
0.4
0.5
20
25
0.6
0.7
0.8
0.9
3.0
VIN=18V, VEN=1.8V
Fpwm=300Hz
20
2.5
2.0
IOUT=2.5mA
15
1.5
10
1.0
IOUT=25mA
5
0.5
0.0
0
1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Duty Cycle
Duty Cycle
Figure 14. PWM Dimming on EN Pin
Figure 15. PWM Dimming on VIN Pin
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
30
0
0.0
0
0.2
15
Figure 13. Current Mirror Ratio vs. LED Current
IOUT Current (mA)
VIN=18V, VEN=1.8V
Fpwm=300Hz
10
IOUT Current (mA)
Figure 12. IOUT Current vs. REXT Voltage
0.1
15
VIN=18V, VEN=1.8V
REXT (k )
0
13
Figure 11. Variation of IOUT Current vs. Output Voltage
10
25
11
Figure 10. Line Regulation
284
30
9
Output Voltage (V)
283
IOUT Current (mA)
7
Input Voltage (V)
100
0.1
IOUT=10mA
0.15
1
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FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Typical Characteristics (Continued)
Unless otherwise noted, CIN = 4.7µF, VEN=1.8V, TA = 25°C, white LED with VF=3.3V at IOUT=10mA.
Figure 16. Turn-On at Full Load
Figure 17. Turn-Off at Full Load
Figure 19. Load Transient Response
(VOUT High to Low)
Figure 18. Load Transient Response
(VOUT Low to High)
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
7
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Typical Characteristics (Continued)
Setting the Output Current Level
External Capacitors
An internally generated reference current is mirrored on
the MOSFETs connected to the outputs IOUT1 and
IOUT2 (pins 1 and 6, respectively). The current mirror
ratio is 275 (typical). The voltage on pin 3 (RSET) is
0.475V in steady state; therefore, the programmed
current through each of the outputs is:
Because the FAN5640 is stable without capacitors on
the outputs, no capacitors are recommended. Typical
input decoupling usually present on incoming supply
rails should suffice in most applications. If necessary, a
small input capacitance may be placed between the
input pin and ground without adverse effects.
IOUT  275 
0.475
REXT
Dropout Limitations
EQ. 1
As for any LDO regulator, there are limitations on how
close the input and output rails can be to maintain
regulation. The minimum difference is referred to as the
dropout. The relevant information is provided in the
Typical Performance curve Dropout Voltage vs. LED
Current (see Figure 8). The equation for the data is:
where REXT is the external resistor connected from pin 3
to ground. Increasing this external programming resistor
reduces the output current. For the maximum rated
25mA rating of each output, the minimum value of the
external resistor is:
REXT  275 
0.475
0.475
 275 
 5.225k
IOUT
0.025
VDO  0.35 V  IOUT  64
EQ. 2
EQ. 3
This is equivalent to an RDS of 64Ω with an additional
offset of 350mV. This equation is helpful in determining
the minimum dissipation in the device and the lowest
input voltage for a given application.
The LED output current accuracy is ±10% for 25mA
current (see the Electrical Characteristics table). In the
worst-case scenario, the calculated value of IOUT can
lead to an error of ±10% in the LED current. Since the
tolerance of REXT also affects the LED current accuracy,
a precision resistor should be chosen to have the least
effect on the overall accuracy of the LED current
(see Figure 12).
Multiple LED Displays
For portable applications, the FAN5640 can be powered
from the output of any typical boost regulator. Multiple
LED displays can be created with the FAN5640 powered
from the output of the FAN5333, as shown in Figure 20.
Note that the output voltage of the FAN5333 depends
upon the number of LEDs in its output string. Being
conscious of the minimum dropout requirements of the
FAN5640; if three series LEDs are required to be
present at its output, then the FAN5333 should have
four series LEDs in its output string.
Floating vs. Tied Outputs
Unused outputs can be left floating. The current through is
zero, regardless of the current programmed at pin 3.
However, ESD protection is enhanced if the unused
output pin is tied to VIN (pin 5).
If the two output pins are tied together, they can deliver
a combined 50mA for the same programming resistor of
5.225kΩ.
L
6.8µH to
10µH
V IN
VIN
CIN
4.7µF
to
10µF
ON
OFF
COUT
0.1µF
to
2.2µF
IOUT1 1
SW
GND
FB
2
5 VIN
RSET 3
4 EN
R EXT
SHDN
GND
SHDN GND
6 IOUT2
FAN5640
FAN5333
Figure 20. LED Display Example
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
8
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Application Information
PWM dimming can be implemented by toggling the
enable (EN) pin (pin 4). The recommended PWM
frequency range is 100Hz to 3kHz. For example, if the
rise time is 2.2µs, the actual duty cycle applied internally
to the output MOSFETs is slightly less than the duty
cycle of the signal applied on the enable pin. This leads
to a slight non-linearity in the measured LED current.
That error is:
IOUT
2.2  fPWM   100%

IOUT _ SET
DPWM
EQ. 4
For example, at a PWM frequency of 3kHz, with an
applied duty cycle of 10%, the typical error is:
IOUT
IOUT _ SET

2.2  3k   100  6.6%
0 .1
EQ. 5
So, if RSET is 5.225kΩ, the theoretically expected LED
current, with a PWM duty cycle of 10%, is 2.5mA.
However, the actual (measured) LED current is less by
6.6%. It is (1-0.066) multiplied by 2.5mA, which is
2.335mA. In this way, the actual LED current for any
PWM duty cycle and frequency can be estimated.
LED Selection
The FAN5640 is designed to drive 2-4 LEDs or a higher
number of monochrome LEDs. The maximum number of
LEDs per channel can be calculated as a function of VIN
and the sum of the forward voltage of each LED at the
maximum specified current. The minimum number of
LEDs driven by FAN5640 is the result of calculating the
maximum power dissipated by the IC in the given
operating conditions. The forward voltage of LEDs
depends upon type of LEDs and the manufacturer. In
terms of maximum number of LEDs and LED current,
refer to the Dropout Voltage vs. LED Current graph in
the Typical Characteristics (see Figure 8).
Input Rail Dimming
The LEDs can also be dimmed by modulating the input
supply rail. See Figure 15, PWM Dimming By VIN Pin,
under Typical Characteristics. A maximum frequency of
1KHz is recommended.
Power Dissipation
At an ambient temperature (TA), the power dissipation
(PD) and the junction temperature (TJ) are related to
each other as described in the following equation:
TJ  TA  PD   JA
EQ. 6
where:
PD  ( VIN  VO )  I OUT _ Total  VIN  IQ 
Manufacturer
Part
Website
HARVATEK
HT-T169TW
www.harvatek.com
NICHIA
NSSW1087
www.nichia.com
VRSET
 VIN  VRSET 
REXT
and
IOUT_Total = IOUT1 + IOUT2.
The quiescent current (IQ) can be found in the Electrical
Characteristics section. The junction-to-ambient thermal
resistance (JA) puts a limit on VO_MAX, IOUT_MAX, and the
maximum dropout (VIN-VO) MAX. This affects the number
of LEDs used, the current used to drive them, and so
on. Ensure that thermal shutdown does not occur. The
formula that correlates all these variables is:
( VIN  VO )MAX 
TJ _ MAX  TA _ MAX
 JA  IOUT _ Total
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
EQ. 7
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9
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
This should be solved for TJ_MAX and the result verified
as less than the over-temperature shutdown threshold of
150ºC (typical). An additional 25ºC margin is
recommended to account for tolerances on the
shutdown threshold; TJ_MAX should not exceed 125ºC.
The JA is dependent on the surrounding PCB layout
and can be around 300ºC/W for an SC-70 package.
This can be improved by providing a heat sink of
surrounding copper ground on the PCB. The addition of
backside copper with vias, stiffeners, and other
enhancements can reduce this value. The heat
contributed by the dissipation of other devices located
nearby must be included in design considerations. Once
the limiting parameters in these two relationships have
been determined, the design can be modified to ensure
that the device remains within specified operating
conditions. If overload conditions are not considered, it
is possible for the device to enter a thermal cycling loop,
in which the circuit enters a shutdown condition, cools,
re-enables, and again overheats and shuts down
repeatedly due to an unmanaged fault condition.
PWM Dimming
SYMM
C
L
2.00±0.20
0.65
A
0.50 MIN
4
6
B
PIN ONE
1.25±0.10
1
1.90
3
0.30
0.15
(0.25)
0.40 MIN
0.10
0.65
A B
1.30
LAND PATTERN RECOMMENDATION
1.30
1.00
0.80
SEE DETAIL A
1.10
0.80
0.10 C
0.10
0.00
C
2.10±0.30
SEATING
PLANE
NOTES: UNLESS OTHERWISE SPECIFIED
GAGE
PLANE
(R0.10)
0.25
0.10
0.20
A) THIS PACKAGE CONFORMS TO EIAJ
SC-88, 1996.
B) ALL DIMENSIONS ARE IN MILLIMETERS.
C) DIMENSIONS DO NOT INCLUDE BURRS
OR MOLD FLASH.
D) DRAWING FILENAME: MKT-MAA06AREV6
30°
0°
0.46
0.26
DETAIL A
SCALE: 60X
Figure 21. 6-Lead SC-70 Package Dimensions
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or
obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the
warranty therein, which covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/packaging/.
© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2
www.fairchildsemi.com
10
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
Physical Dimensions
FAN5640 — Dual High-Side Constant Current Source for High-Voltage Keypad LED Illumination
11
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© 2006 Fairchild Semiconductor Corporation
FAN5640 • Rev. 1.0.2