TB62757FUG
TOSHIBA BiCD Digital Integrated Circuit
Silicon Monolithic
TB62757FUG
Step Up Type DC/DC Converter for White LED
The TB62757FUG is a high efficient Step-Up Type DC/DC
Converter specially designed for constant current driving of
White LED.
This IC can drive 2 to 6 white LEDs connected series using a
Li-ion battery.
This IC contains N-ch MOS-FET Transistor for Coil-Switching,
and LED Current (I
F
) is set with an external resistor.
This IC is especially for driving back light white LEDs in LCD
of PDA, Cellular Phone, or Handy Terminal Equipment.
This device is Pb-free product.
Weight: 0.016 g (typ.)
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
Output over voltage shutdown function:
Switching operation is shut downed when OVD terminal voltage is over 22 V (typ.).
IC package: SSOP6-P-0.95
Switching frequency: 1.1 MHz (typ.)
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TB62757FUG
Block Diagram
SW
4
V
IN
3
Over voltage
detection
Monostable
multivibrator
for
reference
Monostable
multivibrator
for
off time control
CTL
AMP.
OVD
2
Circuit
on/off
Error
AMP.
6 FB
SHDN
1
5
GND
Pin Assignment
(top view)
SHDN
1
6 FB
S
OVD 2
5 GND
V
IN
3
4 SW
Note 1: This IC could be destroyed in some case if amounted in 180° inverse direction.
Please be careful about IC direction in mounting.
Pin Function
Pin No.
Symbol
Function Description
1
SHDN
Voltage-input terminal for IC-enable.
SHDN
=
H
→
Operation Mode, SHDN
=
L
→
Shutdown Mode (IC shutdown)
Please do not open this terminal.
Over voltage detection terminal.
IC switching operation is disabled with detection over voltage.
If the voltage returns to detection level or less, operation is enabled again.
Supply voltage input terminal. (2.8 V to 5.5 V)
Switch terminal for DC/DC converter. Nch MOSFET built-in.
Ground terminal.
LED I
F
setting resister connecting terminal.
2
3
4
5
6
OVD
V
IN
SW
GND
FB
2
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TB62757FUG
I/O Equivalent Pin Circuits
1.
SHDN Terminal
V
IN
2. OVD Terminal
OVD 2
SHDN 1
3. V
IN
Terminal to GND Terminal
V
IN
3
4. SW Terminal
SW 4
GND 5
5. FB Terminal
V
IN
FB 6
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TB62757FUG
Application Note
V
IN
4.7 to 10
µ
H
SW
4
3
V
IN
Over voltage
detection
Monostable
multivibrator
for
reference
Monostable
multivibrator
for
off time control
CTL
AMP.
2
OVD
2.2
µF
SHDN
1
PWM
5
GND
Protection in LED Opened Condition
(OVD Function)
The operation with OVD terminal is available for the protection in case LED Circuit opened.
If load of LED is detached, Nch MOS switching operation is disabled with detection of boost circuit voltage.
(* When the voltage value recovers below the detection voltage value, operation is restarted.)
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16
Ω@20
mA
Circuit
on/off
Error
AMP.
6
FB
1
µF
TB62757FUG
Setting of External Capacitor
In case not using PWM signal to
SHDN
terminal for brightness control, recommended values are
C
1
=
Over 2.2 (µF), C
2
=
Over 1.0 (µF)
In case with PWM signal to
SHDN
terminal for brightness control, recommended values are
C
1
=
Over 4.7 (µF), C
2
=
Under 0.1 (µF).
The recommended capacitor values depend on the Brightness Control Method.
<Please refer the next page or later>
The capacitor value must be considered for gain enough accuracy of brightness with reduction of noise from Input
current changing.
Setting of External Inductor Size
Please select the inductor size with referring this table corresponding to each number of LEDs.
LEDs
2
3
4
5
6
Indictor Size
4.7
µ
H
6.8
µ
H
8.1
µ
H
10
µ
H
Note
LED current I
F
=
20 mA
LED Current I
F
Setting
The resistance between the FB pin and GND, R
SENS
(Ω) is the resistance for the setting the output current.
Depending on the resistance value, it is possible to set the average output current Io (mA).
The average output current Io (mA) can be approximated with the following equation:
I
F
=
(325 [mV]/R
SENS
[Ω])
The current value error is
±5%.
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