TB62756FUG
TOSHIBA BiCD Digital Integrated Circuit Silicon Monolithic
TB62756FUG
Step-up Type DC/DC Converter for White LEDs
The TB62756FUG 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 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
Weight: 0.016 g (typ.)
lighting in color LCDs in PDAs, cellular phones and handy
terminal devices.
The suffix (G) appended to the part number represents a Lead(Pb)-Free product.
Features
•
•
•
•
•
•
Can drive 2 to 6 white LEDs connected series
Variable LED current I
F
is set with a external resistor: 20 mA (typ.) @R
SENS
=
16
Ω
Output power: Available for 400 mW LED loading
High efficiency: 87% @Maximum
IC package: SSOP6-P-0.95 (SOT23-6)
Switching frequency: 1.1 MHz (typ.)
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TB62756FUG
Block Diagram
SW
4
V
IN
3
Monostable
multivibrator
for
reference
Monostable
multivibrator
for
off time control
CTL
AMP.
NC
2
Circuit
on/off
SHDN 1
Error
AMP.
6 FB
5
GND
Pin Assignment
(top view)
SHDN 1
6 FB
Q
(NC) 2
5 GND
V
IN
3
4 SW
Note 1: The IC may break if mounted 180 degrees in reverse. Ensure the device is correctly orientated before
assembley.
Pin Functions
No.
Symbol
Function
Input pin for IC ON/OFF control.
SHDN
=
H
→
Operation Mode, SHDN
=
L
→
Shutdown Mode (IC shutdown)
Please do not open this terminal.
No connection or connected to GND.
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.
Connected to the cathode of LED.
(Note 2)
1
2
3
4
5
6
SHDN
NC
V
IN
SW
GND
FB
Note 2: The NC terminal is not connected to the internal circuit.
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2006-06-14
TB62756FUG
I/O Equivalent Pin Circuits
1.
SHDN
Pin
V
IN
2. NC Pin
NC 2
SHDN 1
The NC pin is not connected to any internal
circuit.
3. SW Pin
SW 4
4. FB Pin
V
IN
FB 6
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2006-06-14
TB62756FUG
Application Circuit Example
V
IN
4.7 to 10
µ
H
SW
4
3
V
IN
Monostable
multivibrator
for
reference
Monostable
multivibrator
for
off time control
CTL
AMP.
NC
2
2.2
µF
V
Z
=
24 V
SHDN 1
PWM
5
GND
Protection at the Time of LED Opening
The zener diode in the application circuit example is necessary for the provision of over-voltage protection for
when 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 I
ZD
control by R
ZD
connection. (R
SENS
=
16
Ω)
S-Di
R
ZD
(
Ω
)
500
100
I
ZD
(mA)
0.6 (typ.)
2.8 (typ.)
GND FB
R
SENS
SW
I
ZD
R
ZD
I
F
1
µ
F
C
2
In order to avoid adverse effects on driver characteristics,
Toshiba recommends a resistance of 500
Ω
or less.
Protection Circuit Application
4
16
Ω@20
mA
Circuit
on/off
Error
AMP.
6
FB
500
Ω
2006-06-14
1
µF
TB62756FUG
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.
Inductance (Unit:
µ
H)
4.7
6.8
4
5
10
6
Number of LEDs
2
3
Note
I
F
=
20 mA
Control of I
F
The resistance R
SENS
is connected between the FB pin and the GND pin.
The average current is controlled by the R
SENS
value, and calculated using the following equation:
I
F
(mA)
=
[325 mV/R
SENS
(Ω)]
Margin of error is
±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 33
µs.
•
•
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>>
I
F
(
mA
) =
325
[
mV
] ×
ON Duty
[%]
R
SENS
[
Ω
]
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2006-06-14
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