LM3502
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SNVS339B – SEPTEMBER 2005 – REVISED MAY 2013
LM3502 Step-Up Converter for White LED Applications
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FEATURES
APPLICATIONS
•
•
•
1
2
•
•
•
•
•
•
•
•
Drive up to 4, 6, 8 or 10 White LEDs for Dual
Display Backlighting
>80% Efficiency
Output Voltage Options: 16V , 25V , 35V, and
44V
Input Under-Voltage Protection
Internal Soft Start Eliminating Inrush Current
1 MHz Constant Switching Frequency
Wide Input Voltage: 2.5V to 5.5V
Small External Components
Low Profile Packages: 0.25V
Fb = 0V, Sw Is Floating
Cntrl = 0V
Cntrl = 1.5V, En1 = En2 = 0V
0.18
All voltages are with respect to the potential at the GND pin.
Min and Max limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely
norm.
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Preliminary Electrical Characteristics (1) (2) (continued)
Limits in standard typeface are for TJ = 25°C. Limits in bold typeface apply over the full operating junction temperature range
(−40°C ≤ TJ ≤ +125°C). Unless otherwise specified, VIN = 2.5V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
250
400
450
450
400
600
750
750
650
800
1050
1050
mA
64
500
nA
1
1.2
MHz
0.55
1.1
Ω
PMOS ON Resistance of IPMOS = 20 mA, En1 = 0V, En2 = 1.5V
VOUT1/VOUT2 Switch
(Figure 4: N1)
5
10
Ω
NMOS ON Resistance of INMOS = 20 mA, En1 = 1.5V, En2 = 0V
VOUT2/Fb Switch
(Figure 4: N2)
2.5
5
Ω
NMOS Power Switch
Current Limit
−16,
−25,
−35,
−44,
IFb
Feedback Pin Bias
Current (3)
Fb = 0.25V
FS
Switching Frequency
RDS(ON)
NMOS Power Switch ON ISw = 500 mA
Resistance
(Figure 4: N1)
ICL
RPDS(ON)
RNDS(ON)
Fb
Fb
Fb
Fb
= 0V
= 0V
= 0V
= 0V
0.8
DMAX
Maximum Duty Cycle
Fb = 0V
ICntrl
Cntrl Pin Input Bias
Current (4)
Cntrl = 2.5V
Cntrl = 0V
ISw
Sw Pin Leakage Current
Sw = 42V, Cntrl = 0V
IVOUT1(OFF)
VOUT1 Pin Leakage
Current (5)
VOUT1 = 14V,
VOUT1 = 23V,
VOUT1 = 32V,
VOUT1 = 42V,
Cntrl
Cntrl
Cntrl
Cntrl
VOUT1 Pin Bias Current
VOUT1 = 14V,
VOUT1 = 23V,
VOUT1 = 32V,
VOUT1 = 42V,
Cntrl
Cntrl
Cntrl
Cntrl
0.01
5
µA
= 0V (16)
= 0V (25)
= 0V (35)
= 0V (44)
0.1
0.1
0.1
0.1
3
3
3
3
µA
= 1.5V
= 1.5V
= 1.5V
= 1.5V
40
50
50
85
80
100
100
140
µA
0.1
3
µA
2.4
2.3
2.5
2.2
(16)
(16)
(25)
(25)
(35)
(35)
(44)
(44)
14.5
14.0
22.5
21.5
32.0
31.0
40.5
39.0
15.5
15
24
23
34
33
42
41
16.5
16.0
25.5
24.5
35.0
34.0
43.5
42.0
PMOS FET Switch
Enabling Threshold
(Figure 4: P1)
Off Threshold (Display Lighting)
On Threshold (Display Lighting)
0.8
0.8
0.3
1.4
NMOS FET Switch
Enabling Threshold
(Figure 4: N2)
Off Threshold (Display Lighting)
On Threshold (Display Lighting)
0.8
0.8
0.3
1.4
Device Enabling
Threshold
Off Threshold
OnThreshold
0.8
0.8
0.3
1.4
8
12
16
7
0.1
14
(5)
(16)
(25)
(35)
(44)
VOUT2 Pin Leakage
Current (5)
Fb = 0V, Cntrl = 0V, VOUT2 = 42V
UVP
Under-Voltage
Protection
On Threshold
Off Threshold
Over-Voltage Protection
On Threshold
Off Threshold
On Threshold
Off Threshold
On Threshold
Off Threshold
On Threshold
Off Threshold
VEn1
VEn2
VCntrl
(6)
TSHDW
Shutdown Delay Time
IEn1
En1 Pin Input Bias
Current
(3)
(4)
(5)
(6)
%
14
IVOUT2
OVP
95
7
0.1
(5)
IVOUT1(ON)
90
En1 = 2.5V
En1 = 0V
µA
V
V
V
V
V
ms
µA
Current flows out of the pin.
Current flows into the pin.
Current flows into the pin.
The on threshold indicates that the LM3502 is no longer switching or regulating LED current, while the off threshold indicates normal
operation.
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Preliminary Electrical Characteristics (1) (2) (continued)
Limits in standard typeface are for TJ = 25°C. Limits in bold typeface apply over the full operating junction temperature range
(−40°C ≤ TJ ≤ +125°C). Unless otherwise specified, VIN = 2.5V.
Symbol
IEn2
Parameter
Conditions
En2 Pin Input Bias
Current
Min
Typ
Max
7
0.1
14
En2 = 2.5V
En2 = 0V
Units
µA
BLOCK DIAGRAM
13
VIN
Sw
2,3
Soft Start
Thermal Shutdown
OVP
Comparator
Current Limit
UVP
Comparator
-
UVP
Reference
Error
Amplifier
Fb
4
OVP
Reference
+
Light Load
Reference
VOUT1
+
-
+
-
Light Load
Comparator
Current Sense
PWM
Comparator
+
P1
N1
Driver Logic
+
Fb
Reference
VOUT2
N2
6
Oscillator
FET Logic
+
-
Duty Limit
Comparator
Shutdown
Comparator
Duty Limit
Reference
7
14
9
AGND
Cntrl
15,16
PGND
10
12 En2
Fb
En1
Figure 4. Block Diagram
Detailed Description of Operation
The LM3502 utilizes an asynchronous current mode pulse-width-modulation (PWM) control scheme to regulate
the feedback voltage over specified load conditions. The DC/DC converter behaves as a controlled current
source for white LED applications. The operation can best be understood by referring to the block diagram in
Figure 4 for the following operational explanation. At the start of each cycle, the oscillator sets the driver logic
and turns on the internal NMOS power device, N1, conducting current through the inductor and reverse biasing
the external diode. The white LED current is supplied by the output capacitor when the internal NMOS power
device, N1, is turned on. The sum of the error amplifier’s output voltage and an internal voltage ramp are
compared with the sensed power NMOS, N1, switch voltage. Once these voltages are equal, the PWM
6
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comparator will then reset the driver logic, thus turning off the internal NMOS power device, N1, and forward
biasing the external diode. The inductor current then flows through the diode to the white LED load and output
capacitor. The inductor current recharges the output capacitor and supplies the current for the white LED load.
The oscillator then resets the driver logic again repeating the process. The output voltage of the error amplifier
controls the current through the inductor. This voltage will increase for larger loads and decrease for smaller
loads limiting the peak current in the inductor and minimizing EMI radiation. The duty limit comparator is always
operational, it prevents the internal NMOS power switch, N1, from being on for more than one oscillator cycle
and conducting large amounts of current. The light load comparator allows the LM3502 to properly regulate
light/small white LED load currents, where regulation becomes difficult for the LM3502’s primary control loop.
Under light load conditions, the LM3502 will enter into a pulse skipping pulse-frequency-mode (PFM) of operation
where the switching frequency will vary with the load.
The LM3502 has 2 control pins, En1 and En2, used for selecting which segment of a single white LED string
network is active for dual display applications. En1 controls the main display (MAIN) segment of the single string
white LED network between pins VOUT1 and VOUT2. En2 controls the sub display (SUB) segment of the single
string white LED network between the VOUT2 and Fb. For a quick review of the LM3502 control pin operational
characteristics, see Figure 5.
When the Cntrl pin is ≥ 1.4V, the LM3502 will enter in low IQ state if both En1 and En2 ≤ 0.3V. At this time, both
the P1 and N2 FETs will turn off. The output voltage will be a diode drop below the supply voltage and the softstart will be reset limiting the peak inductor current at the next start-up.
The LM3502 is designed to control the LED current with a PWM signal without the use of an external RC filter.
Utilizing special circuitry, the LM3502 can operate over a large range of PWM frequencies without restarting the
soft-start allowing for fast recovery at high PWM frequencies. Figure 6 represents a PWM signal driving the Cntrl
pin where tL is defined as the low time of the signal. The following is true:
• If tL < 12ms (typical): The device will stop switching during this time and the soft-start will not be reset allowing
LED current PWM control.
• If tL > 12ms (typical): The device will shutdown and the soft-start will reset to prevent high peak currents at the
next startup. Both the N2 and P1 switches will turn off.
The LM3502 has dedicated protection circuitry active during normal operation to protect the integrated circuit (IC)
and external components. The thermal shutdown circuitry turns off the internal NMOS power device, N1, when
the internal semiconductor junction temperature reaches excessive levels. The LM3502 has a under-voltage
protection (UVP) comparator that disables the internal NMOS power device when battery voltages are too low,
thus preventing an on state where the internal NMOS power device conducts large amounts of current. The overvoltage protection (OVP) comparator prevents the output voltage from increasing beyond the protection limit
when the white LED string network is removed or if there is a white LED failure. OVP allows for the use of low
profile ceramic capacitors at the output. The current though the internal NMOS power device, N1, is monitored to
prevent peak inductor currents from damaging the IC. If during a cycle (cycle=1/switching frequency) the peak
inductor current exceeds the current limit for the LM3502, the internal NMOS power device will be turned off for
the remaining duration of that cycle.
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Shutdown
Cntrl*
En1
En2
Result* (See Figure 1 and Figure 2)
Shutdown
1.4V
0.3V
0.3V
[P1ÆOFF N2ÆOFF N1ÆOFF] or [MAINÆOFF SUBÆOFF N1ÆOFF]
1.4V
1.4V
0.3V
[P1ÆOFF N2ÆON N1ÆSwitching] or [MAINÆON SUBÆOFF N1ÆSwitching]
1.4V
0.3V
1.4V
[P1ÆON N2ÆOFF N1ÆSwitching] or [MAINÆOFF SUBÆON N1ÆSwitching]
1.4V
1.4V
1.4V
[P1ÆOFF N2ÆOFF N1ÆSwitching] or [MAINÆON SUBÆON N1ÆSwitching]
0.3V
0.3V
0.3V
[P1ÆOFF N2ÆOFF N1ÆOFF] or [MAINÆOFF SUBÆOFF N1ÆOFF]
X
0.3V
1.4V
0.3V
[P1ÆOFF N2ÆOFF N1ÆOFF] or [MAINÆOFF SUBÆOFF N1ÆOFF]
X
0.3V
0.3V
1.4V
[P1ÆOFF N2ÆOFF N1ÆOFF] or [MAINÆOFF SUBÆOFF N1ÆOFF]
X
0.3V
1.4V
1.4V
[P1ÆOFF N2ÆOFF N1ÆOFF] or [MAINÆOFF SUBÆOFF N1ÆOFF]
X
Low IQ
X
*Table is only valid for when the Cntrl pin signal is a non-periodic logic signal, not a PWM signal.
Figure 5. Operational Characteristics Table
1.4V
Cntrl
0.3V
tL
(Typ)
Figure 6. Control Signal Waveform
8
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Typical Performance Characteristics
( Circuit in Figure 1: L = DO1608C-223 and D = MBRM140T3. Efficiency: η = POUT/PIN = [(VOUT – VFb) * IOUT]/[VIN * IIN]. TA=
25°C, unless otherwise stated.)
Switching Frequency
vs
Temperature
0.600
1.03
0.580
1.02
-40oC
0.560
0.540
25oC
0.520
125oC
0.500
0.480
0.460
1.00
0.99
0.98
0.97
0.96
0.440
0.95
0.420
0.94
0.400
2.5
3.0
3.5
4.0
VIN = 2.5V
1.01
FREQUENCY (MHz)
NON-SWITCHING IQ (mA)
IQ (Non-Switching)
vs
VIN
4.5
5.0
0.93
-40 -20 0 20 40 60 80 100 120
-30 -10 10 30 50 70 90 110 130
5.5
INPUT VOLTAGE (V)
TEMPERATURE (oC)
Figure 7.
Figure 8.
IQ (Switching)
vs
VIN
IQ (Switching)
vs
Temperature
1.95
4.00
VIN = 2.5V
SWITCHING IQ (mA)
SWITCHING IQ (mA)
3.50
-40oC
3.00
125oC
25oC
2.50
1.90
1.85
1.80
2.00
1.50
2.5
3.0
3.5
4.0
4.5
5.0
1.75
-40 -20 0 20 40 60 80 100 120
-30 -10 10 30 50 70 90 110 130
5.5
INPUT VOLTAGE (V)
TEMPERATURE (oC)
Figure 9.
Figure 10.
10 LED Efficiency
vs
LED Current
8 LED Efficiency
vs
LED Current
90
90
VIN = 5.5V
85
70
VIN = 3.3V
65
60
VIN = 2.7V
VIN = 3V
55
70
50
40
2.5
40
32
42
52
VIN = 2.7V
60
55
45
22
VIN = 3V
65
50
12
VIN = 3.3V
75
45
2
VIN = 4.2V
VIN = 5.5V
80
VIN = 4.2V
75
EFFICIENCY (%)
EFFICIENCY (%)
80
85
62
5.0
LED CURRENT (mA)
7.5 12.5 17.5 22.5 27.5 32.5
10.0 15.0 20.0 25.0 30.0 35.0
LED CURRENT (mA)
Figure 11.
Figure 12.
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Typical Performance Characteristics (continued)
( Circuit in Figure 1: L = DO1608C-223 and D = MBRM140T3. Efficiency: η = POUT/PIN = [(VOUT – VFb) * IOUT]/[VIN * IIN]. TA=
25°C, unless otherwise stated.)
6 LED Efficiency
vs
LED Current
95
95
VIN = 5.5V
VIN = 5.5V
90
85
EFFICIENCY (%)
EFFICIENCY (%)
90
80
VIN = 4.2V
VIN = 3.3V
75
VIN = 3V
70
4 LED Efficiency
vs
LED Current
VIN = 2.7V
85
VIN = 4.2V
80
VIN = 2.7V
75
VIN = 3.3V
65
60
70
2
12
22
32
42
52
62
72
82
2
10 18
LED CURRENT (mA)
Figure 13.
Figure 14.
Cntrl Pin Current
vs
Cntrl Pin Voltage
Maximum Duty Cycle
vs
Temperature
98
25
VIN = 2.5
MAX DUTY CYCLE (%)
CNTRL PIN CURRENT (PA)
30
-40oC
20
15
25oC
10
125oC
97
96
95
5
0
0.0
1.0
2.0
3.0
4.0
94
-40 -20 0 20 40 60 80 100 120
-30 -10 10 30 50 70 90 110 130
5.0
CNTRL PIN VOLTAGE (V)
TEMPERATURE (oC)
Figure 15.
Figure 16.
En1 Pin Current
vs
En1 Pin Voltage
En2 Pin Current
vs
En2 Pin Voltage
25
30
20
EN2 PIN CURRENT (PA)
EN1 PIN CURRENT (PA)
25
-40oC
15
o
25 C
10
o
125 C
5
0
0.0
1.0
2.0
3.0
4.0
20
15
-40oC
10
25oC
125oC
5
0
0.0
5.0
1.0
2.0
3.0
4.0
5.0
EN2 PIN VOLTAGE (V)
EN1 PIN VOLTAGE (V)
Figure 17.
10
26 34 42 50 58 66 74
LED CURRENT (mA)
Figure 18.
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Typical Performance Characteristics (continued)
( Circuit in Figure 1: L = DO1608C-223 and D = MBRM140T3. Efficiency: η = POUT/PIN = [(VOUT – VFb) * IOUT]/[VIN * IIN]. TA=
25°C, unless otherwise stated.)
VOUT1 Pin Current
vs
VOUT1 Pin Voltage
1000
INMOS = 400 mA
140
120
-40oC
100
25oC
80
60
900
POWER NMOS RDS(ON) (m:)
VOUT1 PIN BIAS CURRENT (PA)
160
Power NMOS RDS(ON) (Figure 4: N1)
vs
VIN
o
125 C
40
700
600
25oC
500
300
2.5
0
8
16
24
32
40
-40oC
400
20
0
125oC
800
48
3.0
3.5
VOUT1 PIN VOLTAGE (V)
3.50
4.0
4.5
5.5
Figure 19.
Figure 20.
NMOS RDS(ON) (Figure 4: N2)
vs
VIN
PMOS RDS(ON) (Figure 4: P1)
vs
VIN
10
IPMOS = 20 mA
INMOS = 20 mA
3.00
PMOS SWITCH RDS(ON) (:)
NMOS SWITCH RDS(ON) (:)
5.0
INPUT VOLTAGE (V)
125oC
2.50
2.00
25oC
1.50
o
-40 C
1.00
0.50
0.00
2.5
9
8
125oC
7
6
25oC
5
-40oC
4
3.0
3.5
4.0
4.5
5.0
3
2.0
5.5
12.0
22.0
32.0
42.0
VOUT1 PIN VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 21.
Figure 22.
Feedback Voltage
vs
Temperature
Current Limit (LM3502-16)
vs
VIN
480
-16 CURRENT LIMIT (mA)
460
440
T = 85oC
420
400
T = 25oC
380
360
T = -40oC
340
320
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
Figure 23.
Figure 24.
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Typical Performance Characteristics (continued)
( Circuit in Figure 1: L = DO1608C-223 and D = MBRM140T3. Efficiency: η = POUT/PIN = [(VOUT – VFb) * IOUT]/[VIN * IIN]. TA=
25°C, unless otherwise stated.)
Current Limit (LM3502-16)
vs
Temperature
620
440
Current Limit (LM3502-25)
vs
VIN
T = 85oC
600
-25 CURRENT LIMIT (mA)
-16 CURRENT LIMIT (mA)
420
VIN = 2.5V
400
VIN = 5.5V
380
360
580
T = 25oC
560
540
520
500
T = -40oC
480
340
460
320
-40 -25 -10
5
20
35
50
65
440
2.5
80
o
TEMPERATURE ( C)
-25 CURRENT LIMIT (mA)
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
Figure 25.
Figure 26.
Current Limit (LM3502-25)
vs
Temperature
Current Limit (LM3502-35/44)
vs
Temperature
780
770
VIN = 2.5V
-35/44 CURRENT LIMIT (mA)
620
600
3.0
580
560
VIN = 5.5V
540
520
500
480
460
760
750
740
730
720
VIN = 2.5V
710
440
700
420
-40 -25 -10
690
-40 -25 -10
5
20
35
50 65
80
o
5
20
35
50
65
80
o
TEMPERATURE ( C)
TEMPERATURE ( C)
Figure 27.
Figure 28.
780
Current Limit (LM3502-35/44)
vs
VIN
CURRENT LIMIT (mA)
770
760
85oC
750
740
25oC
-40oC
730
720
710
700
690
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
Figure 29.
12
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APPLICATION INFORMATION
WHITE LED CURRENT SETTING
The LED current is set using the following equation:
VFb
ILED =
R1
where
•
•
•
ILED: White LED Current.
VFb: Feedback Pin Voltage. VFb = 0.25V, Typical.
R1: Current Setting Resistor.
(1)
WHITE LED DIMMING
For dimming the white LED string with a pulse-width-modulated (PWM) signal on the Cntrl pin, care must taken
to balance the tradeoffs between audible noise and white LED brightness control. For best PWM duty cycle vs.
white LED current linearity, the PWM frequency should be between 200Hz and 500Hz. Other PWM frequencies
can be used, but the linearity over input voltage and duty cycle variation will not be as good as what the 200Hz to
500Hz PWM frequency spectrum provides. To minimize audible noise interference, it is recommended that a
output capacitor with minimal susceptibility to piezoelectric induced stresses be used for the particular
applications that require minimal or no audible noise interference.
PWM Signal
VSUPPLY
Sw
VIN
VOUT1
Cntrl
VOUT2
Unconnected
Floating
LM3502
En1
GND
Fb
En2
AGND
PGND
R1
Figure 30.
If VOUT2 is not used , En2 must be grounded
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Inductor Current
tON = DTS
(Vin - Vout)/L
Vin/L
IL (avg)
' iL
Time
TS
Figure 31. Inductor Current Waveform
CONTINUOUS AND DISCONTINUOUS MODES OF OPERATION
Since the LM3502 is a constant frequency pulse-width-modulated step-up regulator, care must be taken to make
sure the maximum duty cycle specification is not violated. The duty cycle equation depends on which mode of
operation the LM3502 is in. The two operational modes of the LM3502 are continuous conduction mode (CCM)
and discontinuous conduction mode (DCM). Continuous conduction mode refers to the mode of operation where
during the switching cycle, the inductor current never goes to and stays at zero for any significant amount of time
during the switching cycle. Discontinuous conduction mode refers to the mode of operation where during the
switching cycle, the inductor current goes to and stays at zero for a significant amount of time during the
switching cycle. Figure 31 illustrates the threshold between CCM and DCM operation. In Figure 31, the inductor
current is right on the CCM/DCM operational threshold. Using this as a reference, a factor can be introduced to
calculate when a particular application is in CCM or DCM operation. R is a CCM/DCM factor we can use to
compute which mode of operation a particular application is in. If R is ≥ 1, then the application is operating in
CCM. Conversely, if R is < 1, the application is operating in DCM. The R factor inequalities are a result of the
components that make up the R factor. From Figure 31, the R factor is equal to the average inductor current,
IL(avg), divided by half the inductor ripple current, ΔiL. Using Figure 31 the following equation can be used to
compute R factor:
2 * IL (avg)
R=
'iL
[IOUT]
IL (avg) =
[(1-D) * Eff]
[VIN * D]
'iL =
[L * Fs]
2
[2 * IOUT * L * Fs * (VOUT) ]
R=
2
[(VIN) * Eff * (VOUT - VIN)]
where
•
•
•
•
•
•
•
•
•
VIN: Input Voltage.
VOUT: Output Voltage.
Eff: Efficiency of the LM3502.
Fs: Switching Frequency.
IOUT: White LED Current/Load Current.
L: Inductance Magnitude/Inductor Value.
D: Duty Cycle for CCM Operation.
ΔiL: Inductor Ripple Current
IL(avg): Average Inductor Current
(2)
For CCM operation, the duty cycle can be computed with:
14
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tON
D=
TS
[VOUT - VIN]
D=
[VOUT]
where
•
•
•
D: Duty Cycle for CCM Operation.
VOUT: Output Voltage.
VIN: Input Voltage.
(3)
For DCM operation, the duty cycle can be computed with:
tON
D=
TS
[2 * IOUT * L * (VOUT - VIN) * Fs]
D=
2
[(VIN) * Eff]
where
•
•
•
•
•
•
D: Duty Cycle for DCM Operation.
VOUT: Output Voltage.
VIN: Input Voltage.
IOUT: White LED Current/Load Current.
Fs: Switching Frequency.
L: Inductor Value/Inductance Magnitude.
(4)
INDUCTOR SELECTION
In order to maintain inductance, an inductor used with the LM3502 should have a saturation current rating larger
than the peak inductor current of the particular application. Inductors with low DCR values contribute decreased
power losses and increased efficiency. The peak inductor current can be computed for both modes of operation:
CCM and DCM.
The cycle-by-cycle peak inductor current for CCM operation can be computed with:
'iL
IPeak | IL (avg) +
2
[VIN * D]
[IOUT]
+
IPeak |
[2 * L * Fs]
[(1 - D) * Eff]
where
•
•
•
•
•
•
•
•
•
VIN: Input Voltage.
Eff: Efficiency of the LM3502.
Fs: Switching Frequency.
IOUT: White LED Current/Load Current.
L: Inductance Magnitude/Inductor Value.
D: Duty Cycle for CCM Operation.
IPEAK: Peak Inductor Current.
ΔiL: Inductor Ripple Current.
IL(avg): Average Inductor Current.
(5)
The cycle-by-cycle peak inductor current for DCM operation can be computed with:
[VIN * D]
IPeak |
[L * Fs]
where
•
VIN: Input Voltage.
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15
LM3502
SNVS339B – SEPTEMBER 2005 – REVISED MAY 2013
•
•
•
•
www.ti.com
Fs: Switching Frequency.
L: Inductance Magnitude/Inductor Value.
D: Duty Cycle for DCM Operation.
IPEAK: Peak Inductor Current.
(6)
The minimum inductance magnitude/inductor value for the LM3502 can be calculated using the following, which
is only valid when the duty cycle is > 0.5:
[VIN * RDS(ON) * ((D/'¶) - 1)]
L>
[1.562 * Fs]
where
•
•
•
•
•
D: Duty Cycle.
D: 1–D.
RDS(ON): NMOS Power Switch ON
VIN: Input Voltage.
L: Inductance Magnitude/Inductor Value.
(7)
This equation gives the value required to prevent subharmonic oscillations. The result of this equation and the
inductor average and ripple current should be accounted for when choosing an inductor value.
Some recommended inductor manufacturers included but are not limited to:
CoilCraft
DO1608C-223
DT1608C-223
www.coilcraft.com
CAPACITOR SELECTION
Multilayer ceramic capacitors are the best choice for use with the LM3502. Multilayer ceramic capacitors have
the lowest equivalent series resistance (ESR). Applied voltage or DC bias, temperature, dielectric material type
(X7R, X5R, Y5V, etc), and manufacturer component tolerance have an affect on the true or effective capacitance
of a ceramic capacitor. Be aware of how your application will affect a particular ceramic capacitor by analyzing
the aforementioned factors of your application. Before selecting a capacitor always consult the capacitor
manufacturer’s data curves to verify the effective or true capacitance in your application.
INPUT CAPACITOR SELECTION
The input capacitor serves as an energy reservoir for the inductor. In addition to acting as an energy reservoir for
the inductor the input capacitor is necessary for the reduction in input voltage ripple and noise experienced by
the LM3502. The reduction in input voltage ripple and noise helps ensure the LM3502’s proper operation, and
reduces the effect of the LM3502 on other devices sharing the same supply voltage. To ensure low input voltage
ripple, the input capacitor must have an extremely low ESR. As a result of the low input voltage ripple
requirement multilayer ceramic capacitors are the best choice. A minimum capacitance of 2.0 µF is required for
normal operation, so consult the capacitor manufacturer’s data curves to verify whether the minimum
capacitance requirement is going to be achieved for a particular application.
OUTPUT CAPACITOR SELECTION
The output capacitor serves as an energy reservoir for the white LED load when the internal power FET switch
(Figure 4: N1) is on or conducting current. The requirements for the output capacitor must include worst case
operation such as when the load opens up and the LM3502 operates in over-voltage protection (OVP) mode
operation. A minimum capacitance of 0.5µF is required to ensure normal operation. Consult the capacitor
manufacturer’s data curves to verify whether the minimum capacitance requirement is going to be achieved for a
particular application.
Some recommended capacitor manufacturers included but are not limited to:
Taiyo
Yuden
GMK212BJ105MD
(0805/35V)
www.t-yuden.com
muRata
GRM40-035X7R105K
(0805/50V)
www.murata.com
16
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TDK
SNVS339B – SEPTEMBER 2005 – REVISED MAY 2013
C3216X7R1H105KT
(1206/50V)
www.tdktca.com
C3216X7R1C475K
(1206/16V)
AVX
08053D105MAT
(0805/25V)
www.avxcorp.com
08056D475KAT
(0805/6.3V)
1206ZD475MAT
(1206/10V)
DIODE SELECTION
To maintain high efficiency it is recommended that the average current rating (IF or IO) of the selected diode
should be larger than the peak inductor current (ILpeak). At the minimum, the average current rating of the diode
should be larger than the maximum LED current. To maintain diode integrity the peak repetitive forward current
(IFRM) must be greater than or equal to the peak inductor current (ILpeak). Diodes with low forward voltage ratings
(VF) and low junction capacitance magnitudes (CJ or CT or CD) are conducive to high efficiency. The chosen
diode must have a reverse breakdown voltage rating (VR and/or VRRM) that is larger than the output voltage
(Vout). No matter what type of diode is chosen, Schottky or not, certain selection criteria must be followed:
1. VR and VRRM > VOUT
2. IF or IO ≥ ILOAD or IOUT
3. IFRM ≥ ILpeak
Some recommended diode manufacturers included but are not limited to:
Vishay
SS12(1A/20V)
www.vishay.com
SS14(1A/40V)
SS16(1A/60V)
On
Semiconductor
MBRM120E
(1A/20V)
www.onsemi.com
MBRS1540T3
(1.5A/40V)
MBR240LT
(2A/40V)
Central
Semiconductor
CMSH1- 40M
(1A/40V)
www.centralsemi.com
SHUTDOWN AND START-UP
On startup, the LM3502 contains special circuitry that limits the peak inductor current which prevents large
current spikes from loading the battery or power supply. When Cntrl ≥ 1.4V and both the En1 and En2 signals
are less than 0.3V, the LM3502 will enter a low IQ state and regulation will end. During this low IQ mode the
output voltage is a diode drop below the supply voltage and the soft-start will be reset to limit the peak inductor
current at the next startup. When both En1 and En2 are less than 0.3V, the P1 PMOS and N2 NMOS switches
will turn off.
When Cntrl < 0.3V for more than 12ms, typicaly, the LM3502 will shutdown and the output voltage will be a diode
drop below the supply voltage. If the Cntrl pin is low for more than 12ms, the soft-start will reset to limit the peak
inductor current at the next startup.
When Cntrl is < 0.3 but for less than 12ms, typically, the device will not shutdown and reset the soft-start but shut
off the NMOS N1 Power Device to allow for PWM contrl of the LED current.
THERMAL SHUTDOWN
The LM3502 stops regulating when the internal semiconductor junction temperature reaches approximately
140°C. The internal thermal shutdown has approximately 20°C of hysteresis which results in the LM3502 turning
back on when the internal semiconductor junction temperature reaches 120°C. When the thermal shutdown
temperature is reached, the softstart is reset to prevent inrush current when the die temperature cools.
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LM3502
SNVS339B – SEPTEMBER 2005 – REVISED MAY 2013
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UNDER VOLTAGE PROTECTION
The LM3502 contains protection circuitry to prevent operation for low input supply voltages. When Vin drops
below 2.3V, typically the LM3502 will no longer regulate. In this mode, the output volage will be one diode drop
below Vin and the softstart will be reset. When Vin increases above 2.4V, typically, the device will begin
regulating again.
OVER VOLTAGE PROTECTION
The LM3502 contains dedicated circuitry for monitoring the output voltage. In the event that the LED network is
disconnected from the LM3502, the output voltage will increase and be limited to 15.5V(typ.) for the 16V version ,
24V(typ.) for the 25V version, 34V(typ.) for the 35V version and 42V(typ.) for the 44V version (see eletrical table
for more details). In the event that the network is reconnected, regulation will resume at the appropriate output
voltage.
LAYOUT CONSIDERATIONS
All components, except for the white LEDs, must be placed as close as possible to the LM3502. The die attach
pad (DAP) must be soldered to the ground plane.
The input bypass capacitor CIN, as shown in Figure 1, must be placed close to the IC and connect between the
VIN and PGND pins. This will reduce copper trace resistance which effects input voltage ripple of the IC. For
additional input voltage filtering, a 100nF bypass capacitor can be placed in parallel with CIN to shunt any high
frequency noise to ground. The output capacitor, COUT, must be placed close to the IC and be connected
between the VOUT1 and PGND pins. Any copper trace connections for the COUT capacitor can increase the series
resistance, which directly effects output voltage ripple and efficiency. The current setting resistor, R1, should be
kept close to the Fb pin to minimize copper trace connections that can inject noise into the system. The ground
connection for the current setting resistor network should connect directly to the PGND pin. The AGND pin
should be tied directly to the PGND pin. Trace connections made to the inductor should be minimized to reduce
power dissipation and increase overall efficiency while reducing EMI radiation. For more details regarding layout
guidelines for switching regulators, refer to Applications Note AN-1149.
18
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SNVS339B – SEPTEMBER 2005 – REVISED MAY 2013
REVISION HISTORY
Changes from Revision A (May 2013) to Revision B
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 18
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19
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM3502ITL-16/NOPB
LIFEBUY
DSBGA
YPA
10
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-40 to 125
SANB
LM3502ITL-25/NOPB
LIFEBUY
DSBGA
YPA
10
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-40 to 125
SAPB
LM3502ITL-44/NOPB
LIFEBUY
DSBGA
YPA
10
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-40 to 125
SDLB
LM3502SQ-16/NOPB
LIFEBUY
WQFN
RGH
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L00048B
LM3502SQ-25/NOPB
LIFEBUY
WQFN
RGH
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L00049B
LM3502SQ-35/NOPB
LIFEBUY
WQFN
RGH
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L00044B
LM3502SQ-44/NOPB
LIFEBUY
WQFN
RGH
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L00050B
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
2-Sep-2015
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
LM3502ITL-16/NOPB
DSBGA
YPA
10
250
178.0
8.4
LM3502ITL-25/NOPB
DSBGA
YPA
10
250
178.0
LM3502ITL-44/NOPB
DSBGA
YPA
10
250
178.0
LM3502SQ-16/NOPB
WQFN
RGH
16
1000
LM3502SQ-25/NOPB
WQFN
RGH
16
LM3502SQ-35/NOPB
WQFN
RGH
LM3502SQ-44/NOPB
WQFN
RGH
2.03
2.21
0.76
4.0
8.0
Q1
8.4
2.03
2.21
0.76
4.0
8.0
Q1
8.4
2.03
2.21
0.76
4.0
8.0
Q1
178.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
1000
178.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
16
1000
178.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
16
1000
178.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
Pack Materials-Page 1
W
Pin1
(mm) Quadrant
PACKAGE MATERIALS INFORMATION
www.ti.com
2-Sep-2015
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM3502ITL-16/NOPB
DSBGA
YPA
10
250
210.0
185.0
35.0
LM3502ITL-25/NOPB
DSBGA
YPA
10
250
210.0
185.0
35.0
LM3502ITL-44/NOPB
DSBGA
YPA
10
250
210.0
185.0
35.0
LM3502SQ-16/NOPB
WQFN
RGH
16
1000
210.0
185.0
35.0
LM3502SQ-25/NOPB
WQFN
RGH
16
1000
210.0
185.0
35.0
LM3502SQ-35/NOPB
WQFN
RGH
16
1000
210.0
185.0
35.0
LM3502SQ-44/NOPB
WQFN
RGH
16
1000
210.0
185.0
35.0
Pack Materials-Page 2
PACKAGE OUTLINE
RGH0016A
WQFN - 0.8 mm max height
SCALE 3.500
WQFN
4.1
3.9
B
A
PIN 1 INDEX AREA
0.5
0.3
0.3
0.2
4.1
3.9
DETAIL
OPTIONAL TERMINAL
TYPICAL
C
0.8 MAX
SEATING PLANE
(0.1)
TYP
2.6 0.1
5
8
SEE TERMINAL
DETAIL
12X 0.5
4
9
4X
1.5
1
12
16X
PIN 1 ID
(OPTIONAL)
13
16
16X
0.3
0.2
0.1
0.05
C A
C
B
0.5
0.3
4214978/A 10/2013
NOTES:
1. All linear dimensions are in millimeters. Dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.
www.ti.com
EXAMPLE BOARD LAYOUT
RGH0016A
WQFN - 0.8 mm max height
WQFN
( 2.6)
SYMM
16
13
SEE DETAILS
16X (0.6)
16X (0.25)
1
12
(0.25) TYP
SYMM
(3.8)
(1)
9
4
12X (0.5)
5X ( 0.2)
VIA
8
5
(1)
(3.8)
LAND PATTERN EXAMPLE
SCALE:15X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
METAL
SOLDER MASK
OPENING
METAL
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK
DEFINED
SOLDER MASK DETAILS
4214978/A 10/2013
NOTES: (continued)
4. This package is designed to be soldered to a thermal pad on the board. For more information, see QFN/SON PCB application report
in literature No. SLUA271 (www.ti.com/lit/slua271).
www.ti.com
EXAMPLE STENCIL DESIGN
RGH0016A
WQFN - 0.8 mm max height
WQFN
SYMM
(0.675)
METAL
TYP
13
16
16X (0.6)
16X (0.25)
12
1
(0.25) TYP
(0.675)
SYMM
(3.8)
12X (0.5)
9
4
8
5
4X
(1.15)
(3.8)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
EXPOSED PAD
78% PRINTED SOLDER COVERAGE BY AREA
SCALE:15X
4214978/A 10/2013
NOTES: (continued)
5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
MECHANICAL DATA
YPA0010
0.600
±0.075
D
E
TLP10XXX (Rev D)
D: Max = 2.124 mm, Min =2.063 mm
E: Max = 1.946 mm, Min =1.885 mm
4215069/A
NOTES:
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
www.ti.com
12/12
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www.ti.com/audio
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www.ti.com/automotive
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www.ti.com/communications
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www.ti.com/computers
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www.dlp.com
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www.ti.com/consumer-apps
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www.ti.com/energy
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interface.ti.com
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www.ti.com/medical
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logic.ti.com
Security
www.ti.com/security
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power.ti.com
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www.ti.com/space-avionics-defense
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microcontroller.ti.com
Video and Imaging
www.ti.com/video
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www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
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