TS1937CX5RF [TSC]
Boost (Step-up) WLED Driver; 升压（升压） WLED驱动器
| 型号： | TS1937CX5RF |
| 厂家： | 
TAIWAN SEMICONDUCTOR COMPANY, LTD |
| 描述： | Boost (Step-up) WLED Driver |
| 文件： | 总8页 (文件大小：381K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
TS1937
Boost (Step-up) WLED Driver
SOT-25
Pin Definition:
1. SW
ꢀ
2. Ground
3. Feedback
4. CTRL
5. Input
General Description
The TS1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The
device can drive 2 ~ 12 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 TS1937 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
Application
●
●
●
●
●
Cellular Phones
●
●
●
●
●
●
●
●
●
Inherently Matched LED Current
Digital Still Cameras
MP3 Players
High Efficiency: 88% Typical
Drives Up to 6 LEDs @ Vin 5V
Drives Up to 12 LEDs @ Vin 12~15V
36V Rugged Bipolar Switch
White LED Backlighting
PDAs, Handheld computers
Fast 1.2MHz Switching Frequency
Requires Only 0.22µF Output Capacitor
PWM dimming control 1KHz to 10KHz
Analog dimming control
Ordering Information
Part No.
Package
SOT-25
Packing
TS1937CX5 RF
3Kpcs / 7” Reel
Typical Application Circuit
ꢀ
1/8
Version: C07
TS1937
Boost (Step-up) WLED Driver
Absolute Maximum Rating
Parameter
Symbol
VIN
Limit
20
Unit
V
Input Voltage
Supply Voltage (Recommended)
FB Voltage
VIN
2.5 ~ 18
10
V
VFB
V
SW Voltage
VSW
VCTRL
TA
36
V
CTRL Voltage
10
V
Ambient Temperature Range
Junction Temperature Range
-40 to +85
-40 to +125
oC
oC
TJ
Electrical Specifications (Ta = 25oC, VIN= VCTRL=3V, CIN=1uF, COUT=0.22uF unless otherwise noted)
Function Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Input Voltage Range
VIN
2.5
--
18
V
Feedback Voltage
FB Pin Bias Current
VFB
IB
Isw=100mA, 66% duty cycle
86
95
104
mV
10
--
45
100
2.5
nA
1.9
mA
Supply Current
IQ
CTRL = 0V
--
0.1
1.2
1.0
1.6
uA
Switching Frequency
FRSW
0.8ꢀ
MHz
Switch Current Limit
Maximum Duty Cycle
Switch Vcesat
ICL
--
85
--
320
90
--
--
mA
%
DTMX
VSAT
ILKG
At Isw = 250mA
Vsw = 5V
High
350
0.01
--
--
mV
µA
V
Switch Leakage Current
--
5
1.5
--
--
VCTRL
Voltage Enable Control
CTRL Pin Bias Current
Low
--
0.4
--
V
ICTRL
Ctrl = 2V
--
65
µA
Thermal Resistance
Note:
θJA
--
220
--
°C/W
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: C07
TS1937
Boost (Step-up) WLED Driver
Functional Block
ꢀ
Pin Description
Pin
Function
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.
1
SW
2
3
Ground
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.
Feedback
VCTRL > 1.8V generates full-scale LED current
4
5
CTRL
Input
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
3/8
Version: C07
TS1937
Boost (Step-up) WLED Driver
Application Information
Operation
The TS1937 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 TS1937 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 TS1937. The Typical switch current is
limited to about 320mA by the chip.
Over Voltage Protection
The TS1937 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 TS1937 will shutdown until input condition
changes to bring it out of the shutdown mode.
Inductor Selection
A 22mH inductor is recommended for most TS1937 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 TS1937 applications.
Capacitor Selection
The small size of ceramic capacitors makes them ideal for TS1937 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: C07
TS1937
Boost (Step-up) WLED Driver
Application Information (Continue)
Reference Design Information
VIN Range
(V)
VOUT Max.
(V)
LED
(Series)
Current
(mA)
Resistor
Efficiency
(%)
L (uH)
(Ω)
5
9
36
36
36
36
22
33
47
68
6pcs
11pcs
12pcs
12pcs
20
20
20
20
4.75
4.75
4.75
4.75
83.5
84.2
84.3
84.6
12
15
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 TS1937 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 TS1937 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
VFB
0
Iout(mA)
0
1.8
1.6
1.4
1.2
1
2.2
0.43
1.8
9.2
19.6
31.1
43.4
63
3.6
6
8.5
0.8
0.6
0.4
0.2
0
12.3
14.5
16.9
19
74
86.4
96.9
102
20
Dimming Control using a DC Voltage
5/8
Version: C07
TS1937
Boost (Step-up) WLED Driver
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
Iout ( mA)
0%
20%
30%
40%
50%
60%
70%
80%
100%
20
17.4
15
12.4
10
8
6.4
4.07
0
PWM : 2V ; 1KHz ; Vin=3.6V
Dimming Control using a Filtered PWM Signal
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)
R1(Ω)
19.1
9.53
7.87
6.34
4.75
5
10
12
15
20
6/8
Version: C07
TS1937
Boost (Step-up) WLED Driver
SOT-25 Mechanical Drawing
SOT-25 DIMENSION
MILLIMETERS
INCHES
MIN
DIM
MIN
0.09
0.30
0.09
2.70
1.40
MAX
1.25
0.50
0.25
3.10
1.80
MAX.
0.0492
0.0197
0.0098
0.1220
0.0709
A+A1
B
C
D
E
0.0354
0.0118
0.0035
0.1063
0.0551
E
1.90 BSC
0.0748 BSC
H
2.40
3.00
0.09449
0.1181
L
0.35 BSC
0.0138 BSC
Ө1
S1
0º
10º
0º
10º
0.95 BSC
0.0374 BSC
Marking Diagram
37 = Device Code
= Year Code
M = Month Code
Y
(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
7/8
Version: C07
TS1937
Boost (Step-up) WLED Driver
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.
8/8
Version: C07
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