TB62752BFUG
TOSHIBA BiCD Digital Integrated Circuit
Silicon Monolithic
TB62752BFUG
Step Up Type DC-DC Converter for White LED
The TB62752BFUG is a high efficient Step-Up Type DC-DC
Converter specially designed for constant current driving of White
LED.
This IC can drive 2-7 white LEDs connected series using a
Li-ion battery.
This IC contains N-ch MOSFET Transistor for Coil-Switching,
and LED current (IF) 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.
Weight: 0.016 g (typ.)
Features
•
•
•
•
•
•
•
2-7 white LEDs connected series.
Variable LED current IF is set with a external resistor: 20 mA (typ.) @RSENS
=
15
Ω
Output power: Available for 800 mW LED loading (VIN=2.8V, 7LEDs, I
F
=
Over 25 mA)
High efficiency: 80% over (using recommended external parts)
Output over voltage shutdown function
: Switching operation is shut downed when OVD terminal voltage is over 29.0V (MIN).
IC package: SSOP6-P-0.95B
Switching frequency: 1.0 MHz (typ.)
Pin Assignment
(top view)
1.
SHDN
6. FB
1.
SHDN
6. FB
P
Week 1 to 26
P
2. OVD
3. VIN
5. GND
4. SW
2. OVD
3. VIN
5. GND
4. SW
Week 27 to 53
Note: This IC could be destroyed in some case if amounted in 180° inverse direction.
Please be careful about IC direction in mounting.
1
2011-06-08
TB62752BFUG
Block Diagram
VIN
22
μ
H
SW
VIN
Driver
I
sens
COMP
R
S
Q
Over voltage
detection
OVD
∑
2.2
μH
1.0
μH
C
1
C
2
Ramp
generator
1.0 MHz
oscillator
Error
AMP.
300 mV
SHDN
FB
15
Ω
@20 mA
Shutdown
function
GND
Pin Function
Pin No.
Symbol
Function Description
1
SHDN
Voltage-input terminal for IC-enable/disable LED-I
F
.
A high input on this pin enables the IC to operate while a low input causes it to shut down. The behavior
of the IC is unpredictable if the input on the pin is undefined. Ensure that the pin is tied to either a high or
low level.
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. N-ch MOSFET built-In.
Ground terminal.
LED I
F
setting resistor connecting terminal.
2
3
4
5
6
OVD
VIN
SW
GND
FB
2
2011-06-08
TB62752BFUG
I/O Equivalent Pin Circuits
1.
SHDN Terminal
VIN
2.
OVD Terminal
OVD 2
SHDN 1
3.
VIN Terminal to GND Terminal
4.
SW Terminal
SW 4
VIN 3
GND 5
5.
FB Terminal
VIN
FB 6
3
2011-06-08
TB62752BFUG
Usage Precautions
Protection in LED Opened Condition
The operation with OVD terminal is available for the protection in case LED circuit opened.
When the voltage of OVD terminal is over 29.0V (MIN), Nch MOSFET switching operation is disabled in the
IC. When the voltage of OVD terminal drops below 29.0V (MIN), Nch MOSFET switching operation becomes
available again.
If load of LED is detached, N-ch MOS switching operation is disabled with detection of boost circuit voltage
and the IC is protected from unexpected over voltage.
Setting of External Capacitor
The recommended values are
C
1
=
2.2 (μF) or more, C
2
=
1.0 (μF) or more
The capacitor of ceramic condenser tends to decrease when voltage is applied.
So, please select the appropriate capacitor in consideration of IC characteristics of withstand voltage and size.
Setting of I
F
Resistance connects between FB pin and GND.
The average current is set by this RSENS value and average current are obtained by the following equation.
I
F
(mA)
=
300 [mV]
RSENS [
Ω
]
Current value error is within
±5%.
Setting of External Inductor Size
Please select the inductor size with referring this table corresponding to each number of LEDs.
[Recommended inductor values]
LEDs
2 to 5
Over 6
Indictor Size
10
μ
H
22
μ
H
Note
LED current I
F
=
20 mA
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2011-06-08
TB62752BFUG
Current Dimming Control
Recommended brightness control circuits are 4 types.
(1)
Input PWM signal to
SHDN
terminal
I
F
can be adjusted with PWM signal by inputting it to
SHDN
terminal.
<<PWM signal frequency>>
•
The recommended PWM signal frequency is from 100 Hz to 10 kHz. There is a possibility to arise the
audible frequency in mounting to the board because it is within the auditory area. The greater the
oscillation frequency is, the greater the error between the actual value and the theoretical value
becomes.
<<Constant number of external condenser>>
•
When the PWM signal is off, the time to drain C
2
of charge depends on the constant number. And so,
the actual value is little different from the theoretical value.
<<PWM input signal>>
•
Set the amplitude of PWM signal within the range of
SHDN
terminal specification.
<<Rush current in inputting>>
•
In case dimming by inputting the PWM signal to the
SHDN
terminal, this IC turns on and off
repeatedly.
And the rush current, which provides the charge to C
2
, arises in turning on. Take care in selecting the
condenser.
<<Current value in control with PWM: Ideal equation>>
I
F
[mA]
=
300 [mV]
×
ON Duty [%]
RSENS [
Ω
]
<<Recommended application>>
VIN
=
2.8 to 5.5 V
22
μ
H
S-Di
VIN
PWM signal
C
1
=
4.7
μF
SW
OVD
FB
GND
RSENS
=
15
Ω
C
2
=
1.0
μF
SHDN
5
2011-06-08
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