View SM8122A_1097205.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

SM8122A White LED Driver IC
OVERVIEW
The SM8122A 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. Since the SM8122A has an over voltage protection circuit built-in, it dispenses with the existing external ZD (zener diode). Besides, the switching frequency of the SM8122A is higher (2.0MHz) than the existing product (SM8121A), so that it can respond to lower inductance value.
FEATURES
I I
PINOUT
(Top view)
I
I
I
I
I I I I I I I I I I
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 (51: 9.8mA, 33: 15.2mA, 24: 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 Over voltage protection circuit built-in Supply voltage range: 2.3 to 5.5V Maximum output voltage: 25V Quiescent current: 820A (typ) Standby current: 1.0A (max) RON (Switching MOS-Tr): 2 (typ) Switching frequency: 2.0MHz (typ) Output current detection accuracy: 2% Package: SOT23-6W (SM8122AH) MSON-6 (SM8122AD)
SOT23-6W
SW
1
6
VDD
VOUT
2
5
VSS
FB
3
4
CE
I
MSON-6
VDD 1
6 5 4
VOUT VSS FB
APPLICATIONS
I I I I I I I I I
Cellular phone Pager Digital still camera Handy terminal PDAs Portable games White LED drive LCD bias supply Flash memory supply
SW 2 CE 3
ORDERING INFORMATION
Device SM8122AH SM8122AD Package SOT23-6W MSON-6
NIPPON PRECISION CIRCUITS INC.--1
SM8122A
PACKAGE DIMENSIONS
(Unit: mm)
I
SOT23-6W
2.9 0.2 1.9 0.2
+ 0.1 0.15 - 0.05
1.8 0.2
2.8 0.2
(0.95)
(0.95) 0 to 15 0.8 0.1 1.1 0.1 0 to 0.1
0.1 + 0.1 0.4 - 0.05 0.2 M
I
MSON-6
0.1MIN
0.1 0.06 MIN1.65
45
0.8 0.05
0.2 0.08
2.0 0.15
1.8 0.15
1.4 0.1
0.5 0.1
MIN1.45
1
6
6
R0
.1
1
0.8 0.1
4
45
3
4
0.6 0.05
3
0.14 0.05 0.038 0.02
0.2 0.08
45
45
R0 .07 5
0.125
1.0 0.1 0.3 0.1
+ 0.1 0.75 - 0
0.018
NIPPON PRECISION CIRCUITS INC.--2
0.75 0.05
0.1 0.05
45
SM8122A
BLOCK DIAGRAM
SW
VOUT
OVP COMP
VDD
Buff PWM COMP ERR AMP
FB
RAMP GENERATOR
VREF SOFT START
CE
OSC
VSS
PIN DESCRIPTION
Number Name SOT23-6W 1 2 3 4 5 6 MSON-6 2 6 4 3 5 1 SW VOUT FB CE VSS VDD O I I Ip1 - - Coil switching Output voltage detection Feed back (Output current detection) Chip enable (High active) GND Power supply I/O Description
1. Input with built-in pull-down resistor
NIPPON PRECISION CIRCUITS INC.--3
SM8122A
SPECIFICATIONS
Absolute Maximum Ratings
Parameter Supply voltage range Input voltage range SW output voltage range SW input current Power dissipation Operating temperature range Storage temperature range Symbol VDD VIN VSW ISW PD Topr Tstg Rating -0.3 to 6.5 VSS - 0.3 to VDD + 0.3 -0.3 to 30 500 250 (Ta = 25C) -40 to 85 -55 to 125 Unit V V V mA mW C C
Electrical Characteristics
VDD = 3.6V, VSS = 0V, Ta = 25C unless otherwise noted
Rating Parameter Supply voltage Maximum output voltage Standby current Quiescent current SW-Tr ON resister SW-Tr leak current Switching frequency Maximum duty Input voltage Pin VDD SW VDD VDD SW SW SW SW CE CE Input current FB VOUT Soft-start time FB voltage Coil inductance Over voltage detection VOUT Over voltage detection release SW FB SW Symbol VDD VOUT ISTB IDD RON ILEAK fOSC Duty VIH VIL ICE IFB IVOUT TSS1 TSS2 VFB LSW VOV VOVR VCE = 3.6V VFB = 0.5V VOUT = 25V Switching stop time Maximum duty restriction time VCE = 0V VFB = 1.0V VFB = 0V ISW = 100mA, VDD = 3.6V VSW = VDD VFB = 0V VFB = 0V Condition min 2.3 - - - - - - 1.8 75 2.0 - - -1.0 60 10 - 0.49 - 25 23 typ 3.6 - - 200 820 2.0 - 2.0 85 - - 5.0 - 82 20 500 0.50 4.7 30.5 28.5 max 5.5 25 1.0 400 1600 3.0 1.0 2.2 90 - 0.6 10 1.0 120 70 - 0.51 10 36 - V V A A A A MHz % V V A A A s s V H V V Unit
NIPPON PRECISION CIRCUITS INC.--4
SM8122A
OPERATION OVERVIEW
L 4.7H
VIN 2.3 to 5.5V
SBD
CIN 4.7F
SW
VOUT LED
OVP COMP
COUT 1.0F
VDD
Buff
PWM COMP
ERR AMP
FB
Enable Disable CE VSS
RAMP GENERATOR OSC
VREF SOFT START
R1
The SM8122A basic structure is a step-up DC/DC converter. The booster control employs Pulse Width Modulation (PWM) which controls the pulse duty cycle (85% max.) at constant frequency (2.0MHz 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 SM8122A features a built-in soft-start function. The soft-start time is approximately 500s from after the chip enable input CE rising edge. During this interval, the maximum duty is restricted.
NIPPON PRECISION CIRCUITS INC.--5
SM8122A
OVP (Over Voltage Protection)
SM8122A is always monitoring the VOUT terminal voltage in order to protect itself from the stress of VOUT over voltage. If SM8122A detects the VOUT over voltage, it immediately stop the switching of the inductor drive transistor. After the VOUT terminal voltage decreases below the release voltage, SM8122A restarts switching the inductor drive transistor. The over voltage is set as approximately 30.5V, the release voltage is approximately 28.5V.
Over voltage detection 30.5V
Over voltage detection
28.5V
VOUT
Over voltage detection release
Over voltage detection release
SW Tr = OFF
SW Tr Switching
SW Tr = OFF
Selecting the Current-setting Resistor (R1)
The SM8122A 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 / ILED
FB VFB=0.5V
ILED=0.5/R1
R1=0.5/ILED
NIPPON PRECISION CIRCUITS INC.--6
SM8122A
Selecting the Inductor (L)
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 x TON) / L For example, if the input voltage VIN is 3.6V, the inductance L is 4.7H, and the SW-Tr ON time TON is 2MHz x 85% = 0.425s, then the peak inductor current Ipeak is (3.6 x 0.425 x 10-6) / (4.7 x 10-6) = 0.326A = 326mA.
Selecting the Capacitors (CIN, COUT)
The recommended capacitances for use with the SM8122A are 4.7F ceramic input capacitor CIN and 1.0F 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 SM8122A 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 x 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.
I
I I
I
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 CIN
VOUT
LED
VDD CE VSS FB
COUT
R1
NIPPON PRECISION CIRCUITS INC.--7
SM8122A
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 (50k) and capacitor C1 (0.1F) provide a PWM signal frequency range of 1kHz to 1MHz. Brightness adjustment using FB pin (DC voltage input)
20
SBD
COUT 1.0F
L 4.7H SW VOUT SM8122 VDD VSS CE R2 20k DC Voltage 0 to 3V R3 100k R1 30
LED
15 LED current [mA]
10
VIN 3.6V
CIN 4.7F
FB
5
0 0.0 0.5 1.0 1.5 DC voltage [V] 2.0 2.5 3.0
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.
R2 x (VDC - VFB) R3 R1
VFB - ILED =
... (1)
If the values R1 = 30, R2 = 20k, R3 = 100k, 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 x (0 - 0.5) 100,000 30
=
0.6 = 20mA 30
... (2)
If the values R1 = 30, R2 = 20k, R3 = 100k, 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 x (3 - 0.5) 100,000 30
=
0 = 0mA 30
... (3)
Taking the above diagram as an example, inserting the values R1 = 30, R2 = 20k, R3 = 100k, 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).
NIPPON PRECISION CIRCUITS INC.--8
SM8122A Brightness adjustment using FB pin (PWM signal input)
SBD
20
COUT 1.0F
L 4.7H
15
SW VOUT SM8122 VDD VSS CE
LED
VIN 3.6V
CIN 4.7F
LED current [mA]
R1 30
10
FB
5
R3 50k R4 50k R2 20k
PWM signal Duty [%]
VPWM [V]
C1 0.1F
0 0.0 0.5 1.0 1.5 VPWM x Duty [V] 2.0 2.5 3.0
Brightness adjustment circuit using FB pin (PWM signal input)
PWM signal vs. LED current
When the brightness is controlled by PWM signal (VPWM x Duty), the LED current (ILED) is given by equation 4.
R2 x (VPWM x Duty - VFB) R3 +R4 R1
VFB - ILED =
... (4)
If the values R1 = 30, R2 = 20k, R3 = 50k, R4 = 50k, 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 x (3 x 0 - 0.5) 50,000 + 50,000 30
=
0.6 = 20mA 30
... (5)
If the values R1 = 30, R2 = 20k, R3 = 50k, R4 = 50k, 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 x (3 x 1 - 0.5) 50,000 + 50,000 30
=
0 = 0mA 30
... (6)
Taking the above diagram as an example, inserting the values R1 = 30, R2 = 20k, R3 = 50k, R4 = 50k, 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).
NIPPON PRECISION CIRCUITS INC.--9
SM8122A
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 500s 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
Average LED current [mA]
COUT 1.0F
L 4.7H SW VOUT SM8122 VDD VSS CE
LED
15.0
100 [Hz] 400 [Hz] 1000 [Hz] 1400 [Hz]
10.0
VIN 3.6V
CIN 4.7F
5.0
FB
0.0
PWM signal R1 25
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 SM8122A device, but of the brightness adjustment method employed.
11.0V
8.1V
COUT
20mA
3.5V 3.5V 3.5V 0.5V
COUT
0mA
2.7V 2.7V 2.7V 0V
Output voltage with LEDs ON
Output voltage with LEDs OFF
CE input signal and output ripple voltage
NIPPON PRECISION CIRCUITS INC.--10
SM8122A
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 1.0F
L 4.7H SW VOUT SM8122 VDD VSS CE
LED
Select signal 2 Low Low
Select signal 1 Low High Low High 2mA
ILED
VIN 3.6V
CIN 4.7F
2 + 5 = 7mA 2 + 12.5 = 14.5mA 2 + 5 + 12.5 = 19.5mA
FB
High
R3 40 Select signal 1 Select signal 2 Tr2 R2 100 Tr1 R1 250
High
NIPPON PRECISION CIRCUITS INC.--11
SM8122A
RECOMMEND PATTERN
SOT23-6W
0.7
1.0
0.95
0.95
Footprint pattern
MSON-6
c
2.4
2.4
2.3
0.225
0.225
45
0.5
0.5
45
0.25
0.25
0.6
1.4
2.0
0.5
0.5
0.5
0.4 0.8 1.0 0.5
0.8 1.0
0.4
Footprint pattern
Metalmask pattern
NIPPON PRECISION CIRCUITS INC.--12
1.4
1.9
SM8122A
Please pay your attention to the following points at time of using the products shown in this document. The products shown in this document (hereinafter "Products") are not intended to be used for the apparatus that exerts harmful influence on human lives due to the defects, failure or malfunction of the Products. Customers are requested to obtain prior written agreement for such use from NIPPON PRECISION CIRCUITS INC. (hereinafter "NPC"). Customers shall be solely responsible for, and indemnify and hold NPC free and harmless from, any and all claims, damages, losses, expenses or lawsuits, due to such use without such agreement. NPC reserves the right to change the specifications of the Products in order to improve the characteristic or reliability thereof. NPC makes no claim or warranty that the contents described in this document dose not infringe any intellectual property right or other similar right owned by third parties. Therefore, NPC shall not be responsible for such problems, even if the use is in accordance with the descriptions provided in this document. Any descriptions including applications, circuits, and the parameters of the Products in this document are for reference to use the Products, and shall not be guaranteed free from defect, inapplicability to the design for the mass-production products without further testing or modification. Customers are requested not to export or re-export, directly or indirectly, the Products to any country or any entity not in compliance with or in violation of the national export administration laws, treaties, orders and regulations. Customers are requested appropriately take steps to obtain required permissions or approvals from appropriate government agencies. NIPPON PRECISION CIRCUITS INC. 15-6, Nihombashi-kabutocho, Chuo-ku, Tokyo 103-0026, Japan Telephone: +81-3-6667-6601 Facsimile: +81-3-6667-6611 http://www.npc.co.jp/ Email: sales@npc.co.jp
NC0323AE 2005.05
NIPPON PRECISION CIRCUITS INC.--13

▲Up To Search▲

Price & Availability of SM8122A

	To Download SM8122A Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .