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 0.22µF, 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
●
●
●
●
●
●
●
●
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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 0.22µF 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
●
●
●
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Cellular Phones
Portable Electronics Devices PDA, GPS
LCD Display Module
White LED Backlighting
Typical Application Circuit
1/8
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
V
IN
V
IN
V
FB
V
SW
V
CTRL
T
A
T
J
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 = 25
o
C, V
IN
= V
CTRL
=3V, C
IN
=1uF, C
OUT
=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 V
CESAT
Switch Leakage Current
Symbol
V
IN
V
FB
I
B
I
Q
F
RSW
I
CL
D
TMX
V
SAT
I
LKG
V
CTL
I
CTL
OVP
Test Conditions
I
SW
=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
µA
V
V
µA
V
CTRL = 0V
--
0.8
--
85
At I
SW
= 250mA
V
SW
= 5V
High
Low
Ctrl = 2V
--
--
1.5
--
--
--
V
CTRL
CTRL Pin Bias Current
Over Voltage Protection
Thermal Resistance
θ
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,
θJA
, and the ambient temperature. The maximum allowable, power dissipation at any
ambient temperature is calculated using: PD(MAX)= [TJ(max)-TA]/θJA . Exceeding the maximum allowable power
dissipation will cause excessive die temperature. All limits at temperature extremes are guaranteed via correlation
using standard statistical methods
2/8
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
3/8
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 22µH 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 1µF input capacitor and a 0.22µF output capacitor are sufficient for most.
4/8
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
Dimming Control using a DC Voltage
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
5/8
Version: D08
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