SM8120

SM8120 NPC | Alldatasheet

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Technical content

NIPPON PRECISION CIRCUITS INC.—1 White LED Driver IC OVERVIEW The SM8120A is a high efficiency step-up DC/DC converter. Due to high voltage CMOS process realizing 24V output supply as maximum value, white LED of 2–4 lights connected in series can be lighted. By connect- ing in series, current variation among LED is eliminated. Current value sent to white LED can be set by exter- nal resistors. In addition, brightness can also be adjusted by control to FB pin or CE pin.

FEATURES

I Boost-up control using PFM I White LED of 2-4 lights (connected in series) lighted I Output current value can be set by external resis- tors (51 Ω : 9.8mA, 33 Ω : 15.2mA, 24 Ω : 20.8mA) I Brightness adjustable by control to FB pin or CE pin I Current variation among LED decreased by high precision I High efficient drive by step-up model I Supply voltage range: 2.4 to 5.5V I Maximum output voltage: 24V I Quiescent current: 80 µ A (typ) I Standby current: 1.0 µ A (max) I R ON (Switching MOS-Tr): 2 Ω (typ) I Maximum switching frequency: 500kHz (typ) I Output current detection accuracy: I Small package: SOT23-5

APPLICATIONS

I Cellular phone I Pager I Digital still camera I Handy terminal I PDAs I Portable games I White LED drive I LCD bias supply I Flash memory supply

ORDERING INFORMATION

(Top view) PACKAGE DIMENSIONS (Unit: mm) Device Package SM8120AH SOT23-5 VDD VSS SW CE FB 1.9 ± 0.2 2.9 ± 0.2 0.20MIN 1.6 − 0.1 + 0.2 0.15 − 0.05 + 0.1 0.12 M 0.8 ± 0.1 0.1 0.95 1.1 ± 0.1 0 ~ 0.10 2.8 − 0.3 + 0.2 0.4 ± 0.1

NIPPON PRECISION CIRCUITS INC.—2 BLOCK DIAGRAM PIN DESCRIPTION CE SW VSS VDD FB COMPBuff QS R VREF SOFT STARTOSC Number Name I/O Description

1 VDD – Power supply

2 VSS – GND

3 SW O Coil switching

4 FB I Feed back (Output current detection)

Chip enable (High active) 1. Input with built-in pull-down resistor

NIPPON PRECISION CIRCUITS INC.—3 SPECIFICATIONS Absolute Maximum Ratings

Electrical Characteristics

V DD = 3.6V , V SS = 0V , Ta = 25 C unless otherwise noted Parameter Symbol Rating Unit Supply voltage range V DD 0.3 to 6.5 V Input voltage range V IN V SS – 0.3 to V DD + 0.3 V SW output voltage range V SW –0.3 to 27 V SW input current I SW 250 mA Power dissipation P D 250 (Ta = 25 C) mW Operating temperature range T opr –40 to 85 C Storage temperature range T stg 55 to 125 C Parameter Pin Symbol Condition Rating Unit min typ max Supply voltage VDD V DD 2.4 3.6 5.5 V Standby current VDD I STB V CE = 0V – – 1.0 µA Quiescent current VDD I DD V FB = 1.0V – 80 120 µA SW-Tr ON resister SW R ON I SW = 100mA, V DD = 3.6V – 2.0 3.0 Ω SW-Tr leak current SW I LEAK V SW = V DD – – 1.0 µA Maximum switching frequency SW f OSC V FB = 0V 450 500 550 kHz Duty SW Duty V FB = 0V 53 60 67 % Input voltage CE V IH 2.0 – – V V IL – – 0.6 V Input current CE I CE V CE = 3.6V – 5.0 10 µA FB I FB V FB Soft-start time SW T SS – 500 – µs FB voltage FB V FB 0.49 0.50 0.51 V

NIPPON PRECISION CIRCUITS INC.—4 OPERATION OVERVIEW The SM8120A basic structure is a step-up DC/DC converter. The booster control employs Pulse Frequency Modulation (PFM) which controls the frequency (500kHz max.) at constant SW-Tr ON time (1.2 µ s 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 SM8120A 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 SW-Tr ON time is restricted to 0.6 µ Selecting the Current-setting Resistor (R1) The SM8120A control stabilizes the voltage on pin FB (0.5V typ.). Hence, the current-setting resistor R1 con- nected between FB and VSS sets the LED current I LED , where the resistance R1 is given by the following equation. 0.5 / I LED SW FB COMPBuff QS R VREF SOFT STARTOSC COUT 1.0µF ZD VSS SBD L 22µH CIN 4.7µF VIN 3.0 to 4.5V CE VDD LED Enable Disable ILED=0.5/R1FB VFB=0.5V R1=0.5/ILED

NIPPON PRECISION CIRCUITS INC.—5 Selecting the Inductor (L) The recommended inductance for use with the SM8120A is 22µH. The inductor DC resistance affects the power efficiency, therefore a low DC resistance inductor is recommended. Note also that the peak inductor cur- rent I peak should not exceed the inductor maximum current rating. In pulsed current mode control, the peak inductor current I peak is given by the following equation. I peak = (V IN T ON ) / L For example, if the input voltage V IN is 3.6V , the inductance L is 22µH, and the SW-Tr ON time T ON is 1.2 µ then the peak inductor current I peak is (3.6 1.2 ) / (2.2 ) = 0.2A = 200mA. Selecting the Capacitors (C IN , C OUT The recommended capacitances for use with the SM8120A are 4.7µF ceramic input capacitor C IN and 1.0µF tantalum output capacitor C OUT . The input capacitor ESR ratings affect the ripple voltage, therefore capacitors with low ESR rating are recommended. When the output capacitor ESR ratings are too low, it affect the response to the FB pin, therefore tantalum capacitors are recommended. The input capacitor should be mounted close to the SM8120A IC. Note that the capacitor voltage ratings should be selected to provide suffi- cient 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. I The inductor L and Schottky barrier diode SBD should be connected close to the pin SW using thick, short circuit wiring. I The input capacitor C IN should be mounted close to the IC. I The IC supply voltage V DD wiring and inductor supply wiring should be isolated, reducing any common impedances. I The ground wiring should be connected at a single point, reducing any common impedances. SW FB L CIN VIN SBD COUT VDD CE VSS LED

NIPPON PRECISION CIRCUITS INC.—6 LED OPEN-CIRCUIT PROTECTION When there is no load (LED open-circuit), the FB pin is pulled-down and then switching occurs at maximum frequency. 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 V ZD range is given by the following relationship, where N is the number of LEDs connected in series, V F MAX is the maximum LED forward-bias voltage drop, V OUT MAX is the SW pin maximum output voltage, V FB is the FB pin voltage, and V SBD is the Schottky-bar- rier diode forward-bias voltage drop. F MAX N) ≤ VZD ≤ (VOUT MAX − VFB − VSBD) When the load is applied using a connector (SM8120A and LEDs on separate boards), the zener diode should be mounted on the same board as the SM8120A 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. 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 resis- tance. Consequently, the output current is limited when the load is removed, and the input current can be con- trolled. VSS FB L 22µH CIN 4.7µF VIN 3.6V SBD COUT 1.0µF LED Open VOUT=VZD+0.5=15.5V IZD=0.5/33=15.15mA33Ω ZD (15V) SW VDD CE IIN=(VOUT IZD)/VIN=65mA SW VSS FB L 22µH CIN 4.7µF VIN 3.6V SBD COUT 1.0µF LED Open VOUT=VZD+0.5=15.5V IZD=0.5/1033=0.48mA33Ω ZD (15V) 1kΩ VDD CE IIN=(VOUT IZD)/VIN=2mA

NIPPON PRECISION CIRCUITS INC.—7 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 coeffi- cients. 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) When the brightness is controlled by DC voltage (V DC) connected to resistor R3, the LED current (I LED) is given by equation 1. If the values R1 = 30 Ω, R2 = 20k Ω, R3 = 100k Ω, VFB = 0.5V , and VDC = 0V are inserted in equation 1, the LED current ILED = 20mA, as shown in equation 2. If the values R1 = 30 Ω, R2 = 20k Ω, R3 = 100k Ω, VFB = 0.5V , and VDC = 3V are inserted in equation 1, the LED current ILED = 0mA, as shown in equation 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). Brightness adjustment circuit using FB pin (DC voltage input) SW VSS FB 30Ω SBD DC Voltage 0 to 3V 100kΩ 20kΩ VDD CE COUT 1.0µF L 22µH CIN 4.7µF VIN 3.6V LED DC voltage vs. LED current DC voltage [V] LED current [mA] R2 × (VDC − VFB) R3ILED = VFB − ... (1) 20,000 × (0 − 0.5) 100,000 30 30 ILED == = 0.5 − 0.6 20mA ... (2) 20,000 × (3 − 0.5) 100,000 30 30 ILED == = 0.5 − 0 0mA ... (3)

NIPPON PRECISION CIRCUITS INC.—8 Brightness adjustment using FB pin (PWM signal input) When the brightness is controlled by PWM signal (V PWM × Duty), the LED current (I LED) is given by equa- tion 4. If the values R1 = 30 Ω, R2 = 20k Ω, R3 = 50k Ω, R4 = 50k Ω, VFB = 0.5V , VPWM = 3V , and Duty = 0% are inserted in equation 4, the LED current ILED = 20mA, as shown in equation 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. 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 I LED of 20mA when Duty = 0% (equation 5) and the minimum LED current I LED of 0mA when Duty = 100% (equa- tion 6). Brightness adjustment circuit using FB pin (PWM signal input) SW VSS FB 30Ω SBD 50kΩ R2 20kΩ VDD CE COUT 1.0µF L 22µH CIN 4.7µF VIN 3.6V LED 50kΩ 0.1µF PWM signal Duty [%] VPWM [V] PWM signal vs. LED current VPWM × Duty [V] LED current [mA] R2 × (VPWM × Duty − VFB) R3 +R4 ILED = VFB − ... (4) 30 30 ILED == = 50,000 + 50,0000.5 − 0.6 20mA ... (5) 30 30 ILED == = 50,000 + 50,0000.5 − 0 0mA ... (6)

NIPPON PRECISION CIRCUITS INC.—9 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, there- fore, 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%. When adjusting the brightness using the CE pin, a ripple voltage synchronized to the PWM signal is generated across the output capacitor C OUT. 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 C OUT, 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. Brightness adjustment circuit using CE pin VSS 25Ω SBD PWM signal VDDSW CEFB COUT 1.0µF CIN 4.7µF VIN 3.6V CIN 4.7µF VIN 3.6V L 22µH LED PWM signal duty vs. LED average current PWM signal duty [%] 50 60 70 80 90 100 0.0 5.0 10.0 15.0 20.0 0 1 02 03 04 0 100Hz 400Hz 1000Hz 1400Hz Average LED current [mA] 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 SM8120A device, but of the brightness adjustment method employed. Output voltage with LEDs ON Output voltage with LEDs OFF CE input signal and output ripple voltage 20mA COUT 3.5V 3.5V 3.5V 0.5V 11.0V 0mA COUT 2.7V 2.7V 2.7V 8.1V

NIPPON PRECISION CIRCUITS INC.—10 Current Switching using External Transistors If only a few brightness steps are required, the LED current can be adjusted by switching the LED current set- ting resistance using external transistors (Tr). 250Ω SBD Select signal 1 Tr1 100Ω COUT 1.0µF L 22µH CIN 4.7µF VIN 3.6V LED Select signal 2 Tr2 40Ω VSS FB SW VDD CE Select signal 2 Select signal 1 I LED Low Low 2mA Low High 2 + 5 = 7mA High Low 2 + 12.5 = 14.5mA High High 2 + 5 + 12.5 = 19.5mA

NIPPON PRECISION CIRCUITS INC.—11 TYPICAL APPLICATION CIRCUITS

2 LEDs

CIN : 2012Y5VIC475Z (TDK) COUT :16MCM225MA (Nippon Chemi-con) L : LQH32CN220K21 (Murata) SBD : RB551V-30 (ROHM) LED : NSCW455 (NICHIA)

3 LEDs

CIN : 2012Y5VIC475Z (TDK) COUT :16MCM225MA (Nippon Chemi-con) L : LQH32CN220K21 (Murata) SBD : RB551V-30 (ROHM) LED : NSCW455 (NICHIA) SW VSS FB SBD ILED COUT 2.2µF R VDD CE L 22µH CIN 4.7µFVIN LED R SBD ILED COUT 2.2µF L 22µH CIN 4.7µFVIN LED SW VSS FB VDD CE 100 10501 5 2 0 I LED [mA] Efficiency [%] VIN = 4.5V VIN = 3.6V VIN = 2.4V 100 10501 5 2 0 I LED [mA] Efficiency [%] VIN = 4.5V VIN = 3.6V VIN = 2.4V VIN [V] Efficiency [%] ILED = 15mA ILED = 5mA ILED = 2mA 100 2.5 3.0 VIN [V] Efficiency [%] ILED = 15mA ILED = 5mA ILED = 2mA 100 VIN [V] ILED [mA] R = 25Ω R = 33Ω R = 50Ω R = 100Ω R = 250Ω 2.5 3.0 ILED [mA] V IN [V] 2.5 3.0 R = 25Ω R = 33Ω R = 50Ω R = 100Ω R = 250Ω

NIPPON PRECISION CIRCUITS INC.—12

4 LEDs

CIN : 2012Y5VIC475Z (TDK) COUT :16MCM225MA (Nippon Chemi-con) L : LQH32CN220K21 (Murata) SBD : RB551V-30 (ROHM) LED : NSCW455 (NICHIA) SBD ILED R COUT 2.2µF L 22µH CIN 4.7µFVIN LED SW VSS FB VDD CE 100Efficiency [%] 10501 5 2 0 ILED [mA] VIN = 4.5V VIN = 3.6V VIN = 2.4V VIN [V] Efficiency [%] ILED = 15mA ILED = 5mA ILED = 2mA 100 ILED [mA] R = 25Ω R = 33Ω R = 50Ω R = 100Ω R = 250Ω V IN [V]

NIPPON PRECISION CIRCUITS INC.—13 FOOTPRINT PATTERN SOT23-5 0.7 1.0 0.95 2.4

NIPPON PRECISION CIRCUITS INC.—14 NC0203BE 2004.01 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 req uested appropriately take steps to obtain required permissions or approvals from appropriate government agencies. NIPPON PRECISION CIRCUITS INC. 4-3, Fukuzumi 2-chome, Koto-ku, Tokyo 135-8430, Japan Telephone: +81-3-3642-6661 Facsimile: +81-3-3642-6698 http://www.npc.co.jp/ Email: sales @npc.co.jp