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YB1522
Step-up DC-DC Converter White LED Driver
Description
The YB1522 is a step-up DC-DC converter; with wide input voltage range from 3V to 16V, which operates as current source to drive up to 3S7P to 3S10P (VIN at 3V to 5V). Series connecting of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The light intensity of these LEDs is proportional to the current passing through them. The YB1522 switches at a fixed frequency of ~930KHz, allowing the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space consideration applications. The YB1522 can drive up to 3S10P white LEDs from a single Li-Ion battery. At automotive (5V/12V) applications with higher conversion efficiency. To control LED brightness, the LED current can be pulsed by applying a PWM (pulse width modulated) signal with a frequency range of 100Hz to 1KHz to the CTRL pin. YB1522 has integrated Latched Over Voltage Protection that prevents damage to the device in case of a high impedance output due to faulty LED or open circuit caused by abnormal conditions.
Features
Built-in Internal Switch 3V to 16V Input Range <1uA Shutdown Current High Efficiency Internal Soft Start Drives up to 3S7P to 3S10P White LEDs(VIN at 3.5V to 5V) Over Voltage Protection 30V Small 5-Lead SOT-23 Package Analog and PWM Dimming Control 100mV Low Reference Voltage
Applications
5" ~ 7" LCD Display Module White LED Backlighting Car TV Handheld and PDA Electronic Books Digital Photo Frame
Typical Application Circuit
Figure 1: Typical Application Circuit YB1522 Rev.1.0 www.yobon.com.tw 1
YB1522
Step-up DC-DC Converter White LED Driver
Pin Configuration
SW GND FB
1 2 3
SOT23-5
5 4
VIN
CTRL
Figure 2: Pin Configuration
Pin Description
Table 1
Pin 1 2 3
NAME SW GND FB
Description Switching Pin. This is the collector of the internal NPN power switch. Connect to inductor and diode. Minimize the metal trace area connected to this pin to reduce EMI. Ground Pin. Connect directly to local ground plane. Feedback Pin. Reference voltage is 100mV. Connect LEDs and a resistor at this pin. LED current is determined by the resistance and CTRL voltage. Shutdown Pin and Dimming Control Pin. VCTRL > 1.8V generates full-scale LED current. VCTRL < 0.4V chip is off. Switching from 0.4V to 2.0V, PWM duty cycle controls the LED current. Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.
4
CTRL
5
VIN
Ordering Information
Order Number YB1522ST25 Package Type SOT23-5 Supplied As 3000 units Tape & Reel Package Marking Please contact sales representative
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
Absolute Maximum Ratings
VIN..........................................................20V SW Voltage .............................................32V FB Voltage ................................................5V CTRL Voltage............................................5V Maximum Junction Temp, TJ ............... 150C Lead Temperature (Soldering 10 sec).......300C
Recommended Operating Conditions
Operating Temperature......... -40C to 85C Supply Voltage............................... 3V~16V SW Voltage...........................................20V
Electrical Characteristics
Table 2 (VIN = 3.3V, CIN = 1uF, COUT = 10F, TA=25C, unless otherwise noted.) Description Input Voltage Range Not Switching Shutdown Feedback Voltage Switch Current Limit FB Pin Bias Current Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Switch Vcesat Switch Leakage Current VCTRL for Full LED Current CTRL Pin Bias Current Over Voltage Protection Over Thermal Protection Thermal Resistance VFB ICL IB FSW DMAX DMIN VSAT ILKG VCTL ICTL OVP OTP JA At ISW = 200mA CTRL = 0.3V Full On Full Off CTRL = 2V 40 30 160 220 1.7 0.3 20 Symbol VIN IQ VFB = 0.3V CTRL = 0V IOUT = 20mA,VOUT = 12.5V Circuit of Figure 1 85% duty cycle 40% duty cycle VFB = 100mV 900 930 90 620 Test Conditions MIN 3 1.2 1.5 0.3 100 650 450 1 960 85 25 180 1 TYP MAX 16 1.7 1 110 Units V mA uA mV mA mA uA KHz % % mV A V V A V C C/W
Note : Absolute maximum ratings are limits beyond which damage to the device may occur. The maximum allowable power dissipation is a function of maximum function temperature, TJ(MAX), the junction to ambient thermal resistance, JA , and the ambient temperature. The maximum allowable, power dissipation at any ambient temperature is calculated using: PD(MAX)= [TJ(MAX)-TA]/JA . Exceeding the maximum allowable power dissipation will cause excessive die temperature. All limits at temperature extremes are guaranteed via correlation using standard statistical methods. YB1522 Rev.1.0 www.yobon.com.tw 3
YB1522
Step-up DC-DC Converter White LED Driver
Typical Performance Characteristics
C1=1uF/16V L1=33uH/CD43
C2=10uF/16V R1=0.71
Output Waveform
Output Ripple
Vin & Efficiency
95% 90% Efficiency (%)
Vin & Iout
180 160
Iout (mA)
85% 80% 75% 70% 65% 60% 2.5 3 3.5 4 4.5 Vin (V) 5 5.5 6
140 120 100 80 2.5 3 3.5 4 4.5 5 5.5 6
Vin (V)
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
C1=1uF/16V L1=33uH/CD43
C2=10uF/16V R1=0.62
Output Waveform
Output Ripple
Vin & Efficiency
88% 86% 84% Efficiency (%) 82% 80% 78% 76% 74% 72% 2.5 3 3.5 4 Vin(V) 4.5 5 5.5 6
Iout(mA) 250 200 150 100 50 0 2.5 3 3.5
Vin & Iout
4 Vin(V)
4.5
5
5.5
6
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
C1=1uF/16V L1=33uH/CD43
C2=10uF/16V R1=0.55
Output Waveform
Output Ripple
Vin & Efficiency
80% 78% Efficiency (%) 76% 74% 72% 70% 68% 66% 2.5 3 3.5 4 4.5 Vin(V) 5 5.5 6 Iout(mA) 200 180 160 140 120 100 80 2.5 3 3.5
Vin & Iout
4
4.5 Vin (V)
5
5.5
6
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
C1=1uF/16V L1=33uH/CD43
C2=10uF/16V R1=0.5
Output Waveform
Output Ripple
Vin & Efficiency
72% 70% Efficiency (%) 68%
Vin & Iout
250 200 Iout (mA) 150 100 50 0
66% 64% 62% 60% 58% 2.5 3 3.5 4 4.5 Vin (V) 5 5.5 6
2.5
3
3.5
4
4.5 Vin (V)
5
5.5
6
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
Typical Performance Characteristics
Supply Current (Vctrl = 0V)
1 0.8 0.6 uA 0.4
2 6 5 4
mA 3
Supply Current (Vctrl = Vin)
0.2 0 2 3 4 5 V 6 7 8 9
1 0 2 3 4 5 V 6 7 8 9
Switching Frequency
932.2 932
Vcesat
250 200 Vcesat ( mV) 150 100 50 0
931.8 931.6 Khz 931.4 931.2 931 930.8 2 3 4 5 6 7 8 9 Vin(V)
50
100
150
200
250
300
350
400
Switching Current ( mA)
Switch Leakage Current
0.5 0.4 0.3 uA 0.2 0.1 0 2 3 4 5 6 7 8 9 Vin (V)
60 50 40 uA 30 20 10 0 2 3
CTRL Pin Bias Current
4
5 Vin(V)
6
7
8
9
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
Function Block
Figure 3: YB1522 Block Diagram
Operation
The YB1522 uses a constant frequency, current mode control scheme to regulate the output LED current. Its operation can be understood by referring to the block diagram in Figure 3. At the start of each oscillator cycle, a voltage proportional to the switch current is added to a ramp output and the resulting sum is fed into the positive terminal of the PWM comparator (comparator-1). When this voltage exceeds the level of the comparator negative input, the peak current has been reached, and the SR latch (in Control Logic) is reset and turns off the power switch. The voltage at the negative input of the comparator comes from the output of the error amplifier. The error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered.
YB1522 Rev.1.0
Application Information
Soft Start and Current Limit The internal soft start circuit minimizes the inrush current during turning on YB1522. The maximum switch current is limited to about 650mA by the chip. LED Current and Dimming Control The LED's current is set by a resistor connected at FB pin to GND using:
I LED =
100mV RLED
The maximum LED current set initially can be reduced by pulse width modulating the CTRL. A better approach is to adjust the feedback voltage for dimming control. Either a DC level signal or a filtered PWM signal can be used to control the LED current as illustrated in Figure 4 and Figure 5 respectively. Using the above different scheme, the LED current can be controlled from 0% to 100% to its maximum value.
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YB1522
Step-up DC-DC Converter White LED Driver
VDC (V) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
VFB (mV) 0 2.2 9.2 19.6 31.1 43.4 63 74 86.4 96.9 102
IOUT (mA) 0 0.43 1.8 3.6 6 8.5 12.3 14.5 16.9 19 20
Duty 0% 20% 30% 40% 50% 60% 70% 80% 100%
IOUT (mA) 20 17.4 15 12.4 10 8 6.4 4.07 0
PWM : 2V ; 1KHz ; Vin=3.6V
Figure 4: Dimming Control Using a DC Voltage
Figure 5: Dimming Control Using a Filtered PWM Signal
YB1522 Rev.1.0
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YB1522
Step-up DC-DC Converter White LED Driver
Over Voltage Protection The YB1522 has an internal over voltage protection circuit which also acts as an open-circuit protection. In the cases of open circuit or the LEDs failure, the LEDs are disconnected from the circuit, and the feedback voltage will be zero. The YB1522 will then switch to a high duty cycle resulting in a high output voltage, which may cause SW pin voltage to exceed its maximum 30V rating. The YB1522 will shutdown automatically until input condition changes to bring it out of the shutdown mode. Inductor Selection A 33uH inductor is recommended for most applications to drive more than 3x7 WLEDs. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1MHz and low DCR (copper wire resistance). Diode Selection To maintain high efficiency, the average current rating of the Schottky diode should be large than the peak inductor current, IPK. Schottky diode with a low forward drop and fast switching speeds are ideal for increase efficiency in portable application. Choose a reverse breakdown of the Schottky diode large than the output voltage. Capacitor Selection Choose low ESR capacitors for the output to minimize output voltage ripple. Multilayer capacitors are a good choice for this as well. A 10uF capacitor is sufficient for 3x7 WLEDs applications. For additional bypassing, a 100nF ceramic capacitor can
YB1522 Rev.1.0
be used to shunt high frequency ripple on the input. The input bypass capacitor CIN, as shown in Figure 1, must be placed close to the IC. This will reduce copper trace resistance which affects 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, should also be placed close to the IC. Any copper trace connections for the COUT capacitor can increase the series resistance, which directly effect output voltage ripple. The feedback network, resister R2 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 feedback resistor network should connect directly to an analog ground plane. The analog ground plane should tie directly to the GND pin. If no analog ground plane is available, the ground connection for the feedback network should tie directly to the GND pin. Trace connections made to the inductor and Schottky diode should be minimized to reduce power dissipation and increase overall efficiency.
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YB1522
Step-up DC-DC Converter White LED Driver
Package Information (SOT23-5)
NOTICE: The information described herein is subject to change without notice. Yobon does not assume any responsibility for use of any circuitry or applications described herein, nor does it convey any patent license. YB1522 Rev.1.0 www.yobon.com.tw 12

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