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TS19370
Boost (Step-up) WLED Driver with OVP
SOT-26
Pin Definition: 1. SW 6. Input 2. Ground 5. OVP 3. Feedback 4. CTRL
General Description
The TS19370 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive 2 ~ 9 LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The output capacitor can be as small as 0.22F, saving space versus alternative solutions. A low 95mV feedback voltage minimizes power loss for better efficiency. Additional feature include over output voltage limiting when LEDs are disconnected. The TS19370 switches at a fixed frequency of 1.2MHz, allowing the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space consideration applications for cellular phone backlighting or other hand held equipment.
Features
Inherently Matched LED Current High Efficiency: 88% Typical Drives Up to 6 LEDs @ Vin 5V Drives Up to 9 LEDs @ Vin 9~15V Over Output Voltage Protection 30V Fast 1.2MHz Switching Frequency Requires Only 0.22F Output Capacitor PWM dimming control 1KHz to 10KHz Analog dimming control
Ordering Information
Part No.
TS19370CX6 RF
Package
SOT-26
Packing
3Kpcs / 7" Reel
Input Voltage vs. Efficiency
Application
Cellular Phones Portable Electronics Devices PDA, GPS LCD Display Module White LED Backlighting
Typical Application Circuit
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Absolute Maximum Rating
Parameter
Input Voltage Supply Voltage (Recommended) FB Voltage SW Voltage CTRL Voltage Ambient Temperature Range Junction Temperature Range
Symbol
VIN VIN VFB VSW VCTRL TA TJ
Limit
20 2.5 ~ 18 10 36 10 -40 to +85 -40 to +125
Unit
V V V V V
o o
C C
Electrical Specifications (Ta = 25oC, VIN= VCTRL=3V, CIN=1uF, COUT=0.22uF unless otherwise noted)
Function Parameter
Input Voltage Range Feedback Voltage FB Pin Bias Current Supply Current Switching Frequency Switch Current Limit Maximum Duty Cycle Switch VCESAT Switch Leakage Current
Symbol
VIN VFB IB IQ FRSW ICL DTMX VSAT ILKG VCTL ICTL OVP
Test Conditions
ISW=100mA, 66% duty cycle
Min
2.5 86 10 --
Typ
-95 45 1.9 0.1 1.2 320 90 350 0.01 --65 30
Max
18 104 100 2.5 1.0 1.6 ---5 -0.4 ---
Units
V mV nA mA uA MHz mA % mV A V V A V
CTRL = 0V
-0.8 -85
At ISW= 250mA VSW = 5V High Low Ctrl = 2V
--1.5 ----
VCTRL
CTRL Pin Bias Current Over Voltage Protection
Thermal Resistance JA -220 -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
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Functional Block
Pin Description
Pin
1 2 3
Function
SW Ground Feedback
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 95mV. 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 04V to 2.0V, PWM duty cycle controls the LED current Over Voltage Protection, 30V Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible
4
CTRL
5 6
OVP Input
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Application Information
Operation
The TS19370 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram. At the start of each oscillator cycle, the RS latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the RS latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this manner, 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.
Minimum Output Current
The TS19370 can regulate three series LEDs connected at low output currents, down to approximately 4mA from a 4.2V supply, without pulse skipping, using the same external components as specified for 20mA operation. As the current is further reduced, the device will begin skipping pulses. This will result in some low frequency ripple, although the LED current remains regulated on an average basis down to zero.
Soft Start and Current Limit
The internal soft start circuit minimizes the inrush current during turning on TS19370. The Typical switch current is limited to about 320mA by the chip.
Over Voltage Protection
The TS19370 has design an internal latched off open-circuit protection circuit, the additional sense pin to detect the voltage when the LEDs are disconnected from the circuit or fail open, the TS19370 will shutdown until input condition changes to bring it out of the shutdown mode.
Inductor Selection
A 22H inductor is recommended for most TS19370 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz 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. A Schottky diode rated at 100mA to 200mA is sufficient for most TS19370 applications.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for TS19370 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1F input capacitor and a 0.22F output capacitor are sufficient for most.
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Application Information (Continue)
LED Current Control
The LED current is controlled by the feedback resistor (R1). The feedback reference is 95mV. The LED current is 95mV/R1. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table 3 for R1 selection are shown below. R1 = 95mV/ILED ILED (mA) 5 10 12 15 20 R1() 19.1 9.53 7.87 6.34 4.75
LED Dimming Control
There are some different types of dimming control circuits: 1. Using a PWM Signal to SHDN Pin With the PWM signal applied to the SHDN pin, the TS19370 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle will turn off the TS19370 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal is 1kHz to 10kHz. The magnitude of the PWM signal should be higher than the minimum SHDN voltage high. For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 4. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. For VDC range from 0V to 2V, the selection of resistors in Figure 4 gives dimming control of LED current from 0mA to 20mA. VDC(V) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 VFB 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
Dimming Control using a DC Voltage
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Application Information (Continue)
2. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. The circuit is shown as follow:
Duty 0% 20% 30% 40% 50% 60% 70% 80%
Iout ( mA) 20 17.4 15 12.4 10 8 6.4 4.07
100% 0 PWM : 2V ; 1KHz ; Vin=3.6V Dimming Control using a Filtered PWM Signal
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
SOT-26 Mechanical Drawing
SOT-26 DIMENSION DIM A A1 B C D E F G H I J 2.60 1.40 2.80 1.00 0.00 0.35 0.10 0.30 5 MILLIMETERS MIN TYP 0.95 BSC 1.9 BSC 2.80 1.50 2.90 1.10 -0.40 0.15 --3.00 1.70 3.10 1.20 0.10 0.50 0.20 0.60 10 0.1024 0.0551 0.1101 0.0394 0.00 0.0138 0.0039 0.0118 5 0.0157 0.0059 --MAX MIN INCHES TYP 0.0374 BSC 0.0748 BSC 0.1102 0.0591 0.1142 0.0433 0.1181 0.0669 0.1220 0.0472 0.0039 0.0197 0.0079 0.0236 10 MAX
Marking Diagram
70 = Device Code Y = Year Code M = Month Code (A=Jan, B=Feb, C=Mar, D=Apl, E=May, F=Jun, G=Jul, H=Aug, I=Sep, J=Oct, K=Nov, L=Dec) L = Lot Code
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Version: D08
TS19370
Boost (Step-up) WLED Driver with OVP
Notice
Specifications of the products displayed herein are subject to change without notice. TSC or anyone on its behalf, assumes no responsibility or liability for any errors or inaccuracies. Information contained herein is intended to provide a product description only. No license, express or implied, to any intellectual property rights is granted by this document. Except as provided in TSC's terms and conditions of sale for such products, TSC assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of TSC products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify TSC for any damages resulting from such improper use or sale.
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Version: D08

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