8121_nd14009e00

SM8121A
White LED Driver IC
OVERVIEW
The SM8121A is a high efficiency step-up DC-DC converter. Due to high voltage CMOS process realizing 25V output supply as
maximum value, 2 to 6 lights of white LED connected in series can be lighted. By connecting in series, current variation among LED is
eliminated. Current value sent to white LED can be set by external resistors. In addition, brightness can also be adjusted by control to FB pin
or CE pin.
FEATURES
PINOUT
■ Boost-up control using PWM
■ 2 to 6 lights of white LED (connected in series) lighted
■ Output current value can be set by external resistors
(51Ω: 9.8mA, 33Ω: 15.2mA, 24Ω: 20.8mA)
■ Brightness adjustable by control to FB pin or CE pin
■ Current variation among LED decreased by high precision
■ High efficient drive by step-up model
■ Supply voltage range: 2.3 to 5.5V
■ Maximum output voltage: 25V
■ Quiescent current: 400μA (typ)
■ Standby current: 1.0μA (max)
■ RON (Switching MOS-Tr): 2Ω(typ)
■ Switching frequency: 1.0MHz (typ)
■ Output current detection accuracy: ±2%
■ Small package: SOT23-5 (SM8121AH)
(Top View)
■ SOT23-5
SW
1
VSS
2
FB
3
5
VDD
4
CE
APPLICATIONS
■ Cellular phone
■ Pager
■ Digital still camera
■ Handy terminal
■ PDAs
■ Portable games
■ White LED drive
■ LCD bias supply
■ Flash memory supply
ORDERING INFORMATION
Device
Package
SM8121AH
SOT23-5
SEIKO NPC CORPORATION - 1
SM8121A
PACKAGE DIMENSIONS
(Unit: mm)
SOT23-5
+ 0.2
1.6 − 0.1
+ 0.2
2.8 − 0.3
0.20MIN
■
+ 0.1
0.15 − 0.05
1.9 ± 0.2
2.9 ± 0.2
0.4 ± 0.1
0 ~ 0.10
0.8 ± 0.1
1.1 ± 0.1
0.12 M
0.95
0.1
0.5
2.0
( 0.3 )
( 0.3 )
3.0 ± 0.1
2.6 ± 0.1
0.3TYP
1.6 ± 0.1
1.1
+ 0.1
0.75 − 0.05
0.2 ± 0.1
0.2 ± 0.1
SON-6
0.125 ± 0.05
■
0.05
+ 0.1
0.2 − 0.05
0.05 M
SEIKO NPC CORPORATION —2
SM8121A
BLOCK DIAGRAM
SW
VDD
Buff
PWM
COMP
FB
ERR
AMP
VREF
RAMP
GENERATOR
CE
OSC
SOFT
START
VSS
PIN DESCRIPTION
Number
Name
I/O
Description
1
SW
O
Coil switching
2
VSS
-
GND
3
FB
I
Feed back (Output current detection)
4
CE
IP*1
Chip enable (High active)
5
VDD
-
Power supply
*1. Input with built-in pull-down resistor
SEIKO NPC CORPORATION - 3
SM8121A
SPECIFICATIONS
Absolute Maximum Ratings
Parameter
Symbol
Rating
Unit
Supply voltage range
VDD
−0.3 to 6.5
V
Input voltage range
VIN
VSS – 0.3 to VDD + 0.3
V
SW output voltage range
VSW
–0.3 to 27
V
SW input current
ISW
500
mA
Power dissipation
PD
250 (Ta = 25°C)
mW
Operating temperature range
Topr
–40 to 85
°C
Storage temperature range
Tstg
−55 to 125
°C
Electrical Characteristics
VDD = 3.6V, VSS = 0V, Ta = 25°C unless otherwise noted
Rating
Parameter
Pin
Symbol
Condition
Unit
min
typ
max
Supply voltage
VDD
VDD
2.3
3.6
5.5
V
Maximum output voltage
SW
VOUT
–
–
25
V
Standby current
VDD
ISTB
VCE = 0V
–
–
1.0
µA
150
300
µA
VDD
IDD
VFB = 1.0V
–
Quiescent current
VFB = 0V
–
400
800
µA
SW-Tr ON resister
SW
RON
ISW = 100mA, VDD = 3.6V
–
2.0
3.0
Ω
SW-Tr leak current
SW
ILEAK
VSW = VDD
–
–
1.0
µA
Switching frequency
SW
fOSC
VFB = 0V
0.9
1.0
1.1
MHz
Maximum duty
SW
Duty
VFB = 0V
65
75
85
%
–
–
V
CE
VIH
2.0
Input voltage
VIL
–
–
0.6
V
CE
ICE
VCE = 3.6V
–
5.0
10
µA
FB
IFB
VFB = 0.5V
–1.0
–
1.0
µA
Soft-start time
SW
TSS
–
500
–
µs
FB voltage
FB
VFB
0.49
0.50
0.51
V
Coil inductance
SW
LSW
–
–
10
µH
Input current
SEIKO NPC CORPORATION —4
SM8121A
Typical Characteristics
VSS = 0V, Ta = 25°C unless otherwise noted
1000
800
600
400
200
100
1000
90
900
Soft-start time (TSS) [µs]
Maximum duty (Duty) [%]
Switching frequency (fosc) [kHz]
1200
80
70
60
50
40
30
20
10
0
2.5
3.5
4.0
4.5
5.0
5.5
2.5
Supply voltage (VDD) [V]
7
6
5
4
3
2
1
4.0
4.5
5.0
4.5
5.0
1.0
0.5
3.0
3.5
4.0
4.5
5.0
3.5
4.0
4.5
5.0
600
500
400
300
200
100
2.5
VDD vs. IDD (VFB = 1.0V)
3.0
3.5
4.0
4.5
5.0
5.5
0.505
0.500
0.495
0.490
0.485
0.480
4
3
2
1
5.0
Supply voltage (VDD) [V]
VDD vs. VFB
5.5
3.5
4.0
4.5
5.0
5.5
10
9
8
7
6
5
4
3
2
1
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
40
30
20
10
0
0
4.5
3.0
50
SW-Tr leak current (ILEAK) [pA]
SW-Tr ON resister (RON) [Ω]
0.510
4.0
25
VDD vs. IFB (VFB = 0.5V)
5
0.515
3.5
50
Supply voltage (VDD) [V]
VDD vs. IDD (VFB = 0V)
0.520
3.0
75
Supply voltage (VDD) [V]
Supply voltage (VDD) [V]
2.5
100
VDD vs. ISTB (VCE = 0V)
700
5.5
5.5
Supply voltage (VDD) [V]
0
0
5.0
125
2.5
FB pin input current (IFB) [pA]
Quiescent current (IDD) [µA]
100
4.5
150
5.5
800
200
4.0
0
2.5
VDD vs. VTH
300
3.5
175
Supply voltage (VDD) [V]
400
3.0
VDD vs. TSS
1.5
5.5
500
3.0
200
Supply voltage (VDD) [V]
2.0
VDD vs. ICE (VCE = VDD)
2.5
300
0
2.5
5.5
0.0
4.0
400
200
Supply voltage (VDD) [V]
Quiescent current (IDD) [µA]
3.5
Standby current (ISTB) [pA]
CE pin input voltage (VTH) [V]
CE pin input current (ICE) [µA]
8
0
FB voltage (VFB) [V]
3.0
2.5
9
3.5
500
VDD vs. Duty
10
3.0
600
Supply voltage (VDD) [V]
VDD vs. fOSC
2.5
700
100
0
3.0
800
2.5
3.0
3.5
4.0
4.5
5.0
Supply voltage (VDD) [V]
VDD vs. RON
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Supply voltage (VDD) [V]
VDD vs. ILEAK
SEIKO NPC CORPORATION —5
SM8121A
100
1000
900
1000
90
80
800
600
400
200
70
60
50
40
30
20
0
25
50
75
0
−50 −25
100
Topr vs. fOSC
25
50
75
7
6
5
4
3
2
1
50
75
1.0
0.5
0
25
50
75
100
50
75
600
500
400
300
200
100
−50 −25
Topr vs. IDD (VFB = 1.0V)
0
25
50
75
100
0.520
0.490
0.485
0.480
−50 −25
4
3
2
1
0
0
25
50
75
100
Operating temperature (Topr) [°C]
Topr vs. VFB
50
75
100
500
450
400
350
300
250
200
150
100
50
0
−50
−50 −25
0
25
50
75
100
2000
SW-Tr leak current (ILEAK) [pA]
SW-Tr ON resister (RON) [Ω]
0.495
25
Topr vs. IFB (VFB = 0.5V)
5
0.500
0
Operating temperature (Topr) [°C]
Topr vs. IDD (VFB = 0V)
0.505
500
Operating temperature (Topr) [°C]
Operating temperature (Topr) [°C]
0.510
1000
Topr vs. ISTB (VCE = 0V)
700
100
0.515
1500
Operating temperature (Topr) [°C]
0
25
2000
−50 −25
FB pin input current (IFB) [pA]
Quiescent current (IDD) [µA]
200
100
2500
Operating temperature (Topr) [°C]
800
300
75
3000
100
Topr vs. VTH
400
50
0
−50 −25
500
25
3500
1.5
100
0
Operating temperature (Topr) [°C]
0.0
0
200
Topr vs. TSS
2.0
Topr vs. ICE (VCE = VDD)
0
−50 −25
400
300
0
−50 −25
100
Standby current (ISTB) [pA]
CE pin input voltage (VTH) [V]
CE pin input current (ICE) [µA]
8
Operating temperature (Topr) [°C]
Quiescent current (IDD) [µA]
0
2.5
9
25
500
Topr vs. Duty
10
0
600
Operating temperature (Topr) [°C]
Operating temperature (Topr) [°C]
0
−50 −25
800
700
100
10
0
−50 −25
FB voltage (VFB) [V]
Soft-start time (TSS) [µs]
1200
Maximum duty (Duty) [%]
Switching frequency (fosc) [kHz]
VDD = 3.6V, VSS = 0V unless otherwise noted
−50 −25
0
25
50
75
100
Operating temperature (Topr) [°C]
Topr vs. RON
1750
1500
1250
1000
750
500
250
0
−50 −25
0
25
50
75
100
Operating temperature (Topr) [°C]
Topr vs. ILEAK
SEIKO NPC CORPORATION —6
SM8121A
OPERATION OVERVIEW
L
10µH
SBD
VIN
2.3 to 5.5V
CIN
4.7µF
SW
FB
Buff
VDD
COUT
1.0µF
LED
ERR
AMP
PWM
COMP
ZD
VREF
RAMP
GENERATOR
Enable
Disable
CE
OSC
SOFT
START
VSS
R1
The SM8121A basic structure is a step-up DC/DC converter. The booster control employs Pulse Width Modulation (PWM) which controls the pulse duty cycle (75% max.) at constant frequency (1.0MHz typ.). The LED
current is set by a current-setting resistor R1 connected between pins FB (with stable voltage of 0.5V typ.) and
VSS.
When the switching transistor SW-Tr is ON, energy is stored in the inductor L. When SW-Tr is rapidly
switched OFF, the energy stored in the inductor generates a voltage across the terminals of the inductor. The
induced voltage, after being added to the input voltage, turns ON the Schottky barrier diode SBD and the
stored energy is transferred to the output capacitor. This sequence of events continues repeatedly, boosting the
output voltage.
The SM8121A features a built-in soft-start function. The soft-start time is approximately 500µs from after the
chip enable input CE rising edge. During this interval, the maximum duty is restricted to 50%.
Selecting the Current-setting Resistor (R1)
The SM8121A control stabilizes the voltage on pin FB (0.5V typ.). Hence, the current-setting resistor R1 connected between FB and VSS sets the LED current ILED, where the resistance R1 is given by the following
equation.
R1 = 0.5 / I LED
FB VFB=0.5V
ILED=0.5/R1
R1=0.5/ILED
SEIKO NPC CORPORATION —7
SM8121A
Selecting the Inductor (L)
The recommended inductance for use with the SM8121A is 10µH. The inductor DC resistance affects the
power efficiency, therefore a low DC resistance inductor is recommended. Note also that the peak inductor current Ipeak should not exceed the inductor maximum current rating. In pulsed current mode control, the peak
inductor current Ipeak is given by the following equation.
Ipeak = (VIN × TON) / L
For example, if the input voltage VIN is 3.6V, the inductance L is 10µH, and the SW-Tr ON time T ON is 1MHz
× 75% = 0.75µs, then the peak inductor current I peak is (3.6 × 0.75 × 10-6) / (10 × 10-6) = 0.27A = 270mA.
Selecting the Capacitors (CIN, COUT)
The recommended capacitances for use with the SM8121A are 4.7µF ceramic input capacitor C IN and 1.0µF
ceramic output capacitor COUT. The capacitor ESR ratings affect the ripple voltage, therefore capacitors with
low ESR rating are recommended. The input capacitor should be mounted close to the SM8121A IC. Note that
the capacitor voltage ratings should be selected to provide sufficient margin for the applied input and output
voltages.
For example, if a lithium-ion battery (2.5 to 4.5V) is connected to the input and 3 white LEDs connected in
series at the output draw 20mA, then the maximum input voltage is 4.5V and the maximum output voltage is
(4.0V × 3 LEDs) + 0.5V = 12.5V. Therefore, the input capacitor should have a voltage rating of 6V, and the
output capacitor should have a voltage rating of 16V.
Selecting the Rectifier Schottky Barrier Diode (SBD)
The rectifier schottky barrier diode forward-direction voltage drop affects the power efficiency, therefore a
Schottky barrier diode with low forward-direction voltage drop is recommended. Note that the diode should be
selected to provide sufficient margin for the rated current and reverse-direction withstand voltage.
Board Layout Notes
The following precautions should be followed for stable device operation.
■
■
■
■
The inductor L and Schottky barrier diode SBD should be connected close to the pin SW using thick, short
circuit wiring.
The input capacitor CIN should be mounted close to the IC.
The IC supply voltage VDD wiring and inductor supply wiring should be isolated, reducing any common
impedances.
The ground wiring should be connected at a single point, reducing any common impedances.
SBD
L
SW
VIN
COUT
LED
VDD
CIN
CE
FB
VSS
R1
SEIKO NPC CORPORATION —8
SM8121A
LED OPEN-CIRCUIT PROTECTION
When there is no load (LED open-circuit), the FB pin is pulled-down and then switching occurs at maximum
duty. Consequently, the output voltage continues to be boosted and the SW pin voltage may exceed the maximum rating of 27V. A zener diode can be added so that it acts as the output load when the LED is open-circuit,
preventing the SW voltage from rising. The zener diode must be selected so that the zener does not breakdown
during normal operation. The zener voltage VZD range is given by the following relationship, where N is the
number of LEDs connected in series, VF MAX is the maximum LED forward-bias voltage drop, VOUT MAX is
the SW pin maximum output voltage, VFB is the FB pin voltage, and VSBD is the Schottky-barrier diode forward-bias voltage drop.
(VF MAX × N) ≤ VZD ≤ (VOUT MAX − VFB − VSBD)
When the load is applied using a connector (SM8121A and LEDs on separate boards), the zener diode should
be mounted on the same board as the SM8121A device so that the SW boost prevention function can operate
when the load is disconnected.
Zener Diode (ZD) Only Connection
When the load is removed (LEDs open circuit), the output voltage is determined by the zener voltage, and the
output current is determined by the output current-setting resistance. Consequently, the output current when the
load is removed is not limited, and thus the input current cannot be controlled.
VOUT=VZD+0.5=15.5V
SBD
COUT
1.0µF
IIN=(VOUT IZD)/VIN=65mA
L
10µH
SW
VIN
3.6V
CIN
4.7µF
VSS
VDD
LED Open
ZD
(15V)
SM8121
CE
FB
33Ω
IZD=0.5/33=15.15mA
Zener Diode (ZD) and Current-Limiting Resistance Connection
When the load is removed (LEDs open circuit), the output voltage is determined by the zener voltage, and the
output current is determined by the sum of the output current-setting resistance and the current-limiting resistance. Consequently, the output current is limited when the load is removed, and the input current can be controlled.
VOUT=VZD+0.5=15.5V
SBD
COUT
1.0µF
IIN=(VOUT IZD)/VIN=2mA
L
10µH
SW
VIN
3.6V
CIN
4.7µF
VSS
FB
VDD
LED Open
ZD
(15V)
SM8121
CE
1kΩ
33Ω
IZD=0.5/1033=0.48mA
SEIKO NPC CORPORATION —9
SM8121A
BRIGHTNESS ADJUSTMENT
Brightness Adjustment using FB Pin
The LED brightness can be adjusted using an input DC control voltage connected through resistor R3 to the FB
pin. Alternatively, the brightness can be controlled by a PWM signal by adding a low-pass filter comprising
resistor R4 and capacitor C1. The PWM signal frequency range is determined by the low-pass filter coefficients. For example, the recommended values for resistor R4 (50kΩ) and capacitor C1 (0.1µF) provide a PWM
signal frequency range of 1kHz to 1MHz.
Brightness adjustment using FB pin (DC voltage input)
20
SBD
COUT
1.0µF
LED current [mA]
15
L
10µH
SW
VIN
3.6V
CIN
4.7µF
VSS
VDD
LED
SM8121
CE
FB
10
5
R2
20kΩ
DC Voltage
0 to 3V
R1
30Ω
R3
100kΩ
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
DC voltage [V]
Brightness adjustment circuit using FB pin
(DC voltage input)
DC voltage vs. LED current
When the brightness is controlled by DC voltage (VDC) connected to resistor R3, the LED current (ILED) is
given by equation 1.
VFB −
ILED =
R2 × (VDC − VFB)
R3
... (1)
R1
If the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V, and VDC = 0V are inserted in equation 1, the
LED current ILED = 20mA, as shown in equation 2.
0.5 −
ILED =
20,000 × (0 − 0.5)
100,000
30
=
0.6
= 20mA
30
... (2)
If the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V, and VDC = 3V are inserted in equation 1, the
LED current ILED = 0mA, as shown in equation 3.
0.5 −
ILED =
20,000 × (3 − 0.5)
100,000
30
=
0
= 0mA
30
... (3)
Taking the above diagram as an example, inserting the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V,
and VDC = 0 to 3V into equation 1 gives the maximum LED current ILED of 20mA when VDC = 0V (equation
2) and the minimum LED current ILED of 0mA when VDC = 3V (equation 3).
SEIKO NPC CORPORATION —10
SM8121A
Brightness adjustment using FB pin (PWM signal input)
SBD
20
COUT
1.0µF
15
SW
VIN
3.6V
CIN
4.7µF
VSS
LED current [mA]
L
10µH
VDD
LED
SM8121
CE
FB
10
5
R3
50kΩ
PWM signal
Duty [%]
R4
50kΩ
R1
30Ω
R2
20kΩ
0
C1
0.1µF
0.0
0.5
1.0
1.5
2.0
2.5
3.0
VPWM × Duty [V]
VPWM [V]
Brightness adjustment circuit using FB pin
(PWM signal input)
PWM signal vs. LED current
When the brightness is controlled by PWM signal (VPWM × Duty), the LED current (ILED) is given by equation 4.
VFB −
ILED =
R2 × (VPWM × Duty − VFB)
R3 +R4
R1
... (4)
If the values R1 = 30Ω, R2 = 20kΩ, R3 = 50kΩ, R4 = 50kΩ, VFB = 0.5V, VPWM = 3V, and Duty = 0% are
inserted in equation 4, the LED current ILED = 20mA, as shown in equation 5.
0.5 −
ILED =
20,000 × (3 × 0 − 0.5)
50,000 + 50,000
30
=
0.6
= 20mA
30
... (5)
If the values R1 = 30Ω, R2 = 20kΩ, R3 = 50kΩ, R4 = 50kΩ, VFB = 0.5V, VPWM = 3V, and Duty = 100% are
inserted in equation 4, the LED current ILED = 0mA, as shown in equation 6.
0.5 −
ILED =
20,000 × (3 × 1 − 0.5)
50,000 + 50,000
30
=
0
= 0mA
30
... (6)
Taking the above diagram as an example, inserting the values R1 = 30Ω, R2 = 20kΩ, R3 = 50kΩ, R4 = 50kΩ,
VFB = 0.5V, VPWM = 3V, and Duty = 0 to 100% into equation 4 gives the maximum LED current ILED of
20mA when Duty = 0% (equation 5) and the minimum LED current ILED of 0mA when Duty = 100% (equation 6).
SEIKO NPC CORPORATION —11
SM8121A
Brightness Adjustment using CE Pin
The LED average current can be adjusted by controlling the duty of a PWM signal input on the CE pin. When
CE goes from LOW to HIGH, the soft start function operates (with 500µs constant soft start time) and, therefore, the LED average current ratio for a given PWM signal duty falls with increasing PWM signal frequency.
Taking this into consideration, the recommended PWM control signal has a frequency range of 100 to 400Hz
with duty cycle range of 10 to 90%.
20.0
SBD
100Hz
COUT
1.0µF
Average LED current [mA]
15.0
L
10µH
SW
VIN
3.6V
VSS
CIN
4.7µF
VDD
LED
SM8121
CE
FB
10.0
1000Hz
1400Hz
5.0
R1
25Ω
PWM signal
400Hz
0.0
0
10
20
30
40
50
60
70
80
90
100
PWM signal duty [%]
Brightness adjustment circuit using CE pin
PWM signal duty vs. LED average current
When adjusting the brightness using the CE pin, a ripple voltage synchronized to the PWM signal is generated
across the output capacitor COUT. The amplitude of the ripple voltage is determined by the number of LEDs
and their forward-bias voltage drop characteristics. If a ceramic capacitor is used for the output capacitor
COUT, an audible noise may be generated due to the ceramic capacitor’s piezoelectric effect. The audible noise
level depends on the ceramic capacitor (capacitance, bias dependency, withstand voltage etc.), LEDs (number,
forward-bias voltage drop etc.), and mounting board (thickness, mounting conditions etc.), and thus should be
verified under actual conditions.
Alternatively, a tantalum capacitor or film capacitor with low piezoelectric effect can be used as the output
capacitor COUT to minimize the noise level, or the brightness can be adjusted using the FB pin as described
earlier. The audible noise generated when using the CE pin is not an inherent phenomena of the SM8121A
device, but of the brightness adjustment method employed.
11.0V
8.1V
3.5V
COUT
20mA
3.5V
2.7V
COUT
0mA
2.7V
3.5V
2.7V
0.5V
0V
Output voltage with LEDs ON
Output voltage with LEDs
OFF
CE input signal and output ripple voltage
SEIKO NPC CORPORATION —12
SM8121A
Current Switching using External Transistors
If only a few brightness steps are required, the LED current can be adjusted by switching the LED current setting resistance using external transistors (Tr).
SBD
COUT
1.0µF
L
10µH
SW
VIN
3.6V
CIN
4.7µF
VSS
FB
VDD
LED
SM8121
Select signal 1
ILED
Low
Low
2mA
Low
High
2 + 5 = 7mA
High
Low
2 + 12.5 = 14.5mA
High
High
2 + 5 + 12.5 = 19.5mA
CE
R3
40Ω
Select signal 1
Select signal 2
Select signal 2
R2
100Ω
R1
250Ω
Tr1
Tr2
SEIKO NPC CORPORATION —13
SM8121A
TYPICAL APPLICATION CIRCUITS
2 LEDs
3 LEDs
SBD
SBD
COUT
1.0µF
COUT
1.0µF
L
10µH
SW
L
10µH
ILED
VDD
SW
ILED
VDD
LED
SM8121
VSS
CIN
4.7µF
VIN
LED
VSS
CIN
4.7µF
VIN
CE
FB
SM8121
CE
FB
R
R
100
95
90
85
80
75
70
65
60
55
50
CIN: 2012Y5VIC 475Z (TDK)
COUT: 2012Y5VIH 105Z (TDK)
L: LQH32CN100K11 (Murata)
SBD: RB551V-30 (ROHM)
LED: NSCW455 (NICHIA)
VIN=4.5V
VIN=3.6V
VIN=2.3V
0
5
10
15
Efficiency [%]
Efficiency [%]
CIN: 2012Y5VIC 475Z (TDK)
COUT: 2012Y5VIH 105Z (TDK)
L: LQH32CN100K11 (Murata)
SBD: RB551V-30 (ROHM)
LED: NSCW455 (NICHIA)
20
100
95
90
85
80
75
70
65
60
55
50
0
100
95
ILED=15mA
90
85
ILED=5mA
80
ILED=2mA
75
70
65
60
55
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Efficiency [%]
Efficiency [%]
5
10
15
20
ILED [mA]
ILED [mA]
100
95
ILED=15mA
90
ILED=5mA
85
80
ILED=2mA
75
70
65
60
55
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
VIN [V]
25
20
R=25Ω
15
R=33Ω
10
R=50Ω
5
R=100Ω
ILED [mA]
25
ILED [mA]
VIN=4.5V
VIN=3.6V
VIN=2.3V
20
R= 5Ω
15
R=33Ω
10
R=50Ω
5
R=100Ω
R=250Ω
R=250Ω
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
SEIKO NPC CORPORATION —14
SM8121A
4 LEDs
5LEDs
SBD
SBD
COUT
1.0µF
COUT
1.0µF
L
10µH
L
10µH
SW
ILED
VDD
SW
ILED
VDD
LED
LED
VSS
CIN
4.7µF
VIN
SM8121
VSS
CIN
4.7µF
VIN
CE
FB
SM8121
CE
FB
R
R
100
95
90
85
80
75
70
65
60
55
50
CIN: 2012Y5VIC 475Z (TDK)
COUT: 2012Y5VIH 105Z (TDK)
L: LQH32CN100K11 (Murata)
SBD: RB551V-30 (ROHM)
LED: NSCW455 (NICHIA)
VIN=4.5V
VIN=3.6V
VIN=2.3V
0
5
10
15
Efficiency [%]
Efficiency [%]
CIN: 2012Y5VIC 475Z (TDK)
COUT: 2012Y5VIH 105Z (TDK)
L: LQH32CN100K11 (Murata)
SBD: RB551V-30 (ROHM)
LED: NSCW455 (NICHIA)
100
95
90
85
80
75
70
65
60
55
50
0
20
10
15
20
100
95
90
ILED=15mA
85
ILED=5mA
80
ILED=2mA
75
70
65
60
55
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
100
95
90
85
80
75
70
65
60
55
50
ILED=15mA
ILED=5mA
Efficiency [%]
Efficiency [%]
5
ILED [mA]
ILED [mA]
ILED=2mA
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
VIN [V]
25
20
R=25Ω
15
R=33Ω
10
R=50Ω
5
R=100Ω
R=250Ω
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
ILED [mA]
25
ILED [mA]
VIN=4.5V
VIN=3.6V
VIN=2.3V
20
R=25Ω
15
R=33Ω
10
R=50Ω
5
R=100Ω
R=250Ω
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
SEIKO NPC CORPORATION —15
SM8121A
6 LEDs
SBD
COUT
1.0µF
L
6.8µH
SW
ILED
VDD
LED
VSS
CIN
4.7µF
VIN
SM8121
CE
FB
R
Efficiency [%]
CIN: 2012Y5VIC 475Z (TDK)
COUT: 2012Y5VIH 105Z (TDK)
L: LQH3N6R8K34 (Murata)
SBD: RB551V-30 (ROHM)
LED: NSCW455 (NICHIA)
100
95
90
85
80
75
70
65
60
55
50
VIN=4.5V
VIN=3.6V
VIN=2.3V
0
5
10
15
20
Efficiency [%]
ILED [mA]
100
95
90
ILED=15mA
85
ILED=5mA
80
ILED=2mA
75
70
65
60
55
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
ILED [mA]
25
20
R=25Ω
15
R=33Ω
10
R=50Ω
5
R=100Ω
R=250Ω
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN [V]
SEIKO NPC CORPORATION —16
SM8121A
EVALUATION BOARD PATTERN
SOT23-5 package
Pattern + Hole (Top view)
Silk + Resist (Top view)
Pattern + Hole (Bottom view)
SON-6 package
Pattern + Hole (Top view)
Silk + Resist (Top view)
Pattern + Hole (Bottom view)
SEIKO NPC CORPORATION —17
SM8121A
FOOTPRINT PATTERN
SOT23-5
SON-6
0.7
2.10
2.4
1.0
0.75
0.25
0.5
0.95
SEIKO NPC CORPORATION —18
SM8121A
Please pay your attention to the following points at time of using the products shown in this document.
1. The products shown in this document (hereinafter ”Products”) are designed and manufactured to the generally accepted standards of
reliability as expected for use in general electronic and electrical equipment, such as personal equipment, machine tools and
measurement equipment. The Products are not designed and manufactured to be used in any other special equipment requiring
extremely high level of reliability and safety, such as aerospace equipment, nuclear power control equipment, medical equipment,
transportation equipment, disaster prevention equipment, security equipment. The Products are not designed and manufactured to be
used for the apparatus that exerts harmful influence on the human lives due to the defects, failure or malfunction of the Products.
If you wish to use the Products in that apparatus, please contact our sales section in advance.
In the event that the Products are used in such apparatus without our prior approval, we assume no responsibility whatsoever for any
damages resulting from the use of that apparatus.
2. NPC reserves the right to change the specifications of the Products in order to improve the characteristics or reliability thereof.
3. The information described in this document is presented only as a guide for using the Products. No responsibility is assumed by us for any
infringements of patents or other rights of the third parties which may result from its use. No license is granted by implication or otherwise
under any patents or other rights of the third parties. Then, we assume no responsibility whatsoever for any damages resulting from that
infringements.
4. The constant of each circuit shown in this document is described as an example, and it is not guaranteed about its value of the mass
production products.
5. In the case of that the Products in this document falls under the foreign exchange and foreign trade control law or other applicable laws and
regulations, approval of the export to be based on those laws and regulations are necessary. Customers are requested appropriately take
steps to obtain required permissions or approvals from appropriate government agencies.
SEIKO NPC CORPORATION
1-9-9, Hatchobori, Chuo-ku,
Tokyo 104-0032, Japan
Telephone: +81-3-5541-6501
Facsimile: +81-3-5541-6510
http://www.npc.co.jp/
Email:sales@npc.co.jp
ND14009-E-00 2014.06
SEIKO NPC CORPORATION - 19