YB1517资料

YB1517

Step-up DC-DC Converter & White LED Driver

Description

The YB1517 is a Current-mode PWM step-up DC-DC converter. It can drive up to 18V at 3.0V input and 30V at 5.0V input. The 1 MHz switching frequency allows it to work with tiny external components, therefore minimize the footprint and cost in space consideration products.

One of the major applications for YB1517 is in the dc to dc converter and OLED power supply and TFT panel power supply.

When using YB1517 for white LED driving, it is not recommended to control LED brightness by applying a PWM signal to the CTRL pin, because the built-in soft-start circuit might interfere the start-up operation of YB1517 and cause lower brightness. It operates as current source to drive up to 5 white LEDs in series at 3.0V input and up to 8 white LEDs at 5.0V input. 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.

YB1517 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

• 900 KHz current-mode PWM converter • • • • • • • • •

Built-in internal switch

Adjustable output voltage up to 30V 2.7V to 16V input range <1uA shutdown current Internal Soft Start

Drives up to 5 white LEDs

Tiny Inductor and Capacitors allowed Small 5-Lead SOT-23 package 220mV Low Reference Voltage

Applications

• • • • • • •

LCD Display Module White LED Backlighting PDAs, GPS terminals Digital Cameras Cellular Phone Electronic Books

Portable Applications

Typical Application Circuit

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YB1517

Step-up DC-DC Converter & White LED Driver

Pin Configuration

Figure 3 : YB1517 Pin Configuration

Pin Description

Table 1

Description Pin NAME Switching Pin. This is the collector of the internal NPN power SW switch. Connect to inductor and diode. Minimize the metal 1 trace area connected to this pin to reduce EMI. GND Ground Pin. Connect directly to local ground plane. 2 Feedback Pin. Reference voltage is 220mV. When connecting

LEDs and a resistor at this pin, LED current is determined by

FB 3

the resistance and CTRL voltage.

Shutdown Pin and Dimming Control pin.

VCTRL > 1.8V generates full-scale LED current

CTRL VCTRL < 0.4V chip is off 4

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

VIN 5 the device as possible

Ordering Information

Table 2 Order Number Supplied as Package Marking YB1517ST25 3000 units Tape & Reel Y58 F

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YB1517

Step-up DC-DC Converter & White LED Driver

Absolute Maximum Ratings

VIN.................................................................................20V SW Voltage....................................................................35V FB Voltage.......................................................................5V CTRL Voltage...................................................................5V Maximum Junction Temp,TJ (not 2)............................150°C Lead Temperature (Soldering 10 sec).........................250°C

Recommended Operating Conditions

Operating Temperature (note 3).........................-40°C~85°C Supply Voltage....................................................2.7 V~16V SW Voltage....................................................................30V ESD Susceptibility (HBM)..............................................2KV ESD Susceptibility (MM)...............................................200V

Thermal Resistance (SOT-25, θJA).......................250℃/W Internal Power Disspation (SOT-25, PD)......................0.4W

Electricity Characteristics

Table 3 (TA=25°C, Vin=3.3V, L=22uH, Cin=1uF, Cout=4.7uF unless otherwise noted)

Function Parameter Test Conditions Min Typ Max Units Symbol

Vin Input Voltage Range 2.7 16 V IQ Not Switching VFB = 0.5V 1.2 1.5 1.7 mA (Quiescent

Shutdown CTRL = 0V 0.3 1 uA

Current)

Iout=20mA,Vout = 6V VFB Feedback Voltage 210 220 230 mV Circuit of Figure 2 100% duty cycle 850 900 1000 mA ICL Switch Current Limit 400 mA 40% duty cycle IB FB Pin Bias Current VFB=220mV 1 uA FRSW Switching Frequency 850 900 950 KHz DTMX Maximum Duty Cycle 85 %

DTMN Minimum duty cycle 20 25 % VSAT Switch Vcesat At Isw = 200mA 180 mV ILKG Switch Leakage Current Ctrl = 0.5V 1 μA Full On 1.7 V VCTRL for Full LED VCTL

current Full Off 0.3 V ICTL CTRL Pin Bias Current Ctrl = 2V 40 μA OVP Over Voltage Protection 34 V θJA Thermal Resistance 220 °C/W Note:

Absolute maximum ratings are limits beyond which damage to the device may occur. The maximum

allowable, power dissipation at any ambient temperature is calculated using: PD(MAX)= [TJ(max)-TA]/θJA .

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YB1517

Step-up DC-DC Converter & White LED Driver

Typical Characteristics

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YB1517

Step-up DC-DC Converter & White LED Driver

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YB1517

Step-up DC-DC Converter & White LED Driver

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YB1517

Step-up DC-DC Converter & White LED Driver

Functional Block

Figure3:YB1517BlockDiagram

Operation

The YB1517 uses a constant frequency, current mode control scheme to regulate the output voltage. 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.

Application Information

Soft Start and Current Limit

The internal soft start circuit minimizes the inrush current during turning on YB1517. The maximum switch current is limited to about 900 mA by the chip.

Over Voltage Protection

The YB1517 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 YB1517 will then switch to a high duty cycle resulting in a high output voltage, which may cause SW pin voltage to exceed its maximum 34V rating. The YB1517 will shutdown automatically until

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Step-up DC-DC Converter & White LED Driver

input condition changes to bring it out of the shutdown mode.

Inductor Selection

A 22uH inductor is recommended for most applications to the dc to dc converter and OLED supply and TFT panel power supply . 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.

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.

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 4.7uF capacitor is sufficient for most

applications. For additional bypassing, a

100nF ceramic capacitor can 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

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YB1517

Step-up DC-DC Converter & White LED Driver

Figure 4 : Typical Application Circuit

Figure 5 : TFT Panel Power Application Circuit

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YB1517

Step-up DC-DC Converter & White LED Driver

Package Description

All the contains in this datasheet are not assuming any responsibility for use of any circuitry described no circuit patent license are implied and Yobon reserves the right at any time without notice to change said circuitry and specifications.

Yobon Inc. would like to receive your feedback with your recommends and suggestions that is always welcome and with our appreciations.

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