TB62736FUG
TOSHIBA BiCD Digital Integrated Circuit Silicon Monolithic
TB62736FUG
Step-up Type DC-DC Converter for White LEDs
The TB62736FUG is a high efficiency step-up type DC-DC
converter that is designed especially for use as a constant current
driver of white LEDs.
It is possible to drive 2 to 6 white LEDs connected in series using
a lithium-ion battery.
This IC incorporates an N-ch-MOS FET transistor required for
switching of an external inductor.
The forward current of the LEDs can be controlled by an external
resistor.
This IC is best suited for use as a driver of white LED back
lighting in color LCDs in PDAs, cellular phones and handy
terminal devices.
Weight: 0.016 g (typ.)
Features
•
•
•
•
•
•
Brightness control function with changing drive current:
LED current I
F
=
25% to 100% (analog input)
LED current values controlled by external resistance
Output power
High efficiency
Switching Frequency
: 20 mA (typ.) @ RSENS=16
Ω
: 400 mW
: maximum 87% (when used with components as recommended herein)
: 1.1 MHz(Typ.)
IC package: SSOP6-P-0.95B (SOT23-6)
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TB62736FUG
Block Diagram
4
3
VIN
Reference
Mono Multi
Off Time
Control
Mono Multi
CTL
AMP.
Level
Detect
Error
AMP.
1
SHDN
GND
CTL
AMP.
5
6
SW
2
NC
FB
Pin Assignment (top view)
SHDN
１
6
FB
SHDN
１
6
FB
M
Week 1 to 26
M
(NC)
2
5
GND
4
SW
(NC)
2
5
GND
4
SW
VIN
3
VIN
3
Week 27 to 53
Note 1:
The IC may break if mounted 180 degrees in reverse. Ensure the device is correctly orientated before assembly
.
Pin Functions
No.
Symbol
Function
Input pin for IC ON/OFF control and variable LED I
F
.
0 to 0.5 V : Shutdown Mode (IC shutdown)
1
SHDN
1.0 V to 2.5 V : I
F
= 25 to 100% Variable
Over 2.5 V : I
F
= 100%
PWM signal input for I
F
control (see p.5)
2
3
4
5
6
NC
VIN
SW
GND
FB
No Connection or Connected to GND (Note 2)
Supply voltage pin. Supply voltage range : 2.8 V to 5.5 V
DC-DC converter switching pin – switch incorporates N-ch MOSFET
Ground pin
LED I
F
setting resistor connecting terminal.
Note 2:The NC terminal is not connected to the internal circuit, so placing it on another terminal pattern does not
represent a problem.
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TB62736FUG
I/O Equivalent Pin Circuits
1. SHDN
pin
VIN
2. NC
pin
SHDN
1
NC
2
The NC pin is not connected to any internal circuit,
so placing it on another terminal pattern does not
present a problem.
3.
SW
pin
4.
FB
pin
SW
4
VIN
FB
6
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TB62736FUG
Protection at the time of LED opening
The zener diode in the application circuit example is necessary for the provision of over-voltage protection in the
event the LED becomes open. As the IC does not incorporate a voltage protection circuit, it is strongly advised that
a zener diode be connected.
The zener diode should satisfy the following conditions:
i)
Less than maximum output voltage of 24 V
ii) Greater than the total series LED V
F
iii) Less than the maximum output capacitance C
2
.
Moreover, by connecting a protection circuit such as R_ZD in the figure below, it is possible to control the output
current when the LED becomes open, and to use a zener diode of lower tolerance.
An example of IZD control by R_ZD connection. (RSENS
=
16
Ω)
S-Di
R_ZD (Ω)
500
100
IZD (mA)
Around 0.6
Around 2.8
GND FB
RSENS
SW
IZD
R_ZD
I
F
1
μF
C2
In order to avoid adverse effects on driver characteristics,
Toshiba recommends a resistance of 500 ohms or less.
Protection circuit application
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TB62736FUG
Output-side Capacitor Setting
It is recommended that the value of C
2
be equal to, or greater than 1.0 (μF).
External Inductor Size Setting
For each number of LEDs, the selected inductance should be greater than the value indicated in the table below.
Number of LEDs
2
3
4
5
6
10
Inductance (Unit:
μH)
4.7
6.8
I
F
=
20 mA
Note
Control of I
F
The resistance RSENS is connected between the FB pin and the GND pin.
The average current is controlled by the RSENS value, and calculated using the following equation:
I
F
(mA) = [ 325 mV / RSENS(Ω) ]
Margin of error is ±5%.
Current control using SHDN pin
The IF current set by the RSENS pin resistance can be varied in the range of 25 to 100%.
Linearity error at VA conversion is ±10%.
SHDN Voltage
VSHDN=0 V to 0.5 V VSHDN=1 V to 2.5 V
VSHDN>2.5 V
I
F
Valuable Rate
0
25 - 100
100
SHDN input - output rate/output current
VIN=3.0V
Note
UNIT : %
100
80
IF rate (%)
60
40
20
0
1.0
25
20
IF(mA)
15
10
IF rate
IF
5
0
1.3
1.6
1.9
VSHDN(V)
2.2
2.5
Dimming using PWM signal input
A dimming function can also by applied using a PWM signal.
[Notes]
▪When
using a PWM signal, the minimum pulse width of the PWM should be greater than 33μs.
▪Duty
ratio of PWM function should be set at 10% to 90%.
▪The
recommended PWM frequency should be 100 Hz to 10 kHz.
<<Output current is calculated using the following equation>>
325[mV]
×
ON Duty [%]
IF(mA) =
RSENS [Ω]
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2010-06-24
PCB设计
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