TS19371
Boost (Step-up) WLED Driver with OVP
SOT-26
Pin Definition:
1. SW
6. VIN
2. GND
5. OVP
3. FB
4. CTRL
General Description
The TS19371 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The
device can drive up to 126 LEDs (9S14P) from a 12V supply. The output capacitor can be as small as 4.7µF,
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 TS19371
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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●
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●
●
●
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Inherently Matched LED Current
High Efficiency: 89% Typical
Drives Up to 9 LEDs Series @ Vin 9~15V
Drives Up to 126 LEDs (9S14P) @ Vin 12~15V
Drives Up to 6 (1W) LEDs Series @ Vin 12V
Over Output Voltage Protection 30V (SOT-26)
Fast 1.2MHz Switching Frequency
Requires Only 4.7µF Output Capacitor
PWM Dimming Control 1kHz to 10kHz
Analog Dimming Control
Ordering Information
Part No.
TS19371CX6 RF
TS19371CX6 RFG
Note:
Package
SOT-26
SOT-26
Packing
3kpcs / 7” Reel
3kpcs / 7” Reel
“G” denotes for Halogen- and Antimony-free as those which
contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br +
Cl) and <1000ppm antimony compounds.
Application
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Cellular Phones
Portable Electronics Devices PDA, GPS
LCD Display Module
White LED Backlighting
MR-16 Lighting
Input Voltage vs. Efficiency
Typical Application Circuit
1/8
Version: H14
TS19371
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
(Note 1)
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
(T
C
= 25
o
C, V
IN
= V
CTRL
=3V, C
IN
=1uF, C
OUT
=0.22μF unless otherwise noted)
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
Voltage Enable Control
CTRL Pin Bias Current
Over Voltage Protection
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
=180mA,
V
IN
=5V
Min
2.5
80
10
--
Typ
--
95
45
2.1
0.1
1.2
650
90
350
0.01
--
--
65
30
Max
18
110
100
3.0
1.0
1.6
--
--
--
5
--
0.4
--
--
Units
V
mV
nA
mA
μA
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
--
--
--
Thermal Information
(Note 2)
Parameter
Thermal Resistance - Junction to Ambient
Symbol
R
ӨJA
Test Conditions
Min
--
Typ
220
Max
--
Units
°C/W
Note
1:
Absolute maximum ratings are limits beyond which damage to the device may occur.
Note 2:
The maximum allowable power dissipation is a function of maximum function temperature, T
J
(max), the
junction to ambient thermal resistance, R
θJA
, and the ambient temperature. The maximum allowable, power
dissipation at any ambient temperature is calculated using: PD(MAX)=[T
J
(max)-T
A
]/R
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: H14
TS19371
Boost (Step-up) WLED Driver with OVP
Functional Block
Pin Description
Pin
1
2
3
Function
SW
Ground
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 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.
4
CTRL
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.
5
6
OVP
VIN
3/8
Version: H14
TS19371
Boost (Step-up) WLED Driver with OVP
Application Information
Operation
The TS19371 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.
Soft Start and Current Limit
The internal soft start circuit minimizes the inrush current during turning on TS19371. The Typical switch current is
limited to about 650mA by the chip.
Over Voltage Protection
The TS19371 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 TS19371 will shutdown until input
condition changes to bring it out of the shutdown mode.
Inductor Selection
A 10uH inductor is recommended for most TS19371 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
Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for TS19371
applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode while the
diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and
diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward
voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching
frequency of the TS19371. A Schottky diode rated at 1000mA is sufficient for most TS19371 applications.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for TS19371 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 4.7µF input capacitor and a 4.7µF output capacitor are sufficient for most TS19371
applications.
LED Current Control
The LED current is controlled by the feedback resistor (R1). The feedback reference is 95mV. The LED current is
95mV/R1. The formula and table 3 for R1 selection are shown below. R1=95mV/I
LED
I
LED
(mA)
5
10
12
15
20
R1(Ω)
19.1
9.53
7.87
6.34
4.75
4/8
Version: H14
TS19371
Boost (Step-up) WLED Driver with OVP
Application Information (Continue)
Typical Application Circuit
Reference Design Information
VIN Range
(V)
5
9
12
15
VLED
(V)
19.8
29.7
29.7
29.7
L (μH)
22
33
47
68
LED
(Series)
6pcs
9pcs
9pcs
9pcs
LED
(Parallel)
14
14
14
14
Current
(Series/mA)
20
20
20
20
Resistor
(Ω)
4.75
4.75
4.75
4.75
Efficiency
(%)
81.2
83.6
87.2
88.4
Typical Application Circuit for 1W x 6pcs LEDs
Reference Design Information
VIN Range
(V)
12~15
VLED.
(V)
19.8
L (μH)
68
1W LED
(Series)
6pcs
Current
(mA)
350
Resistor
(Ω)
0.22
Efficiency
(%)
88
5/8
Version: H14
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