TB62752AFUG_datasheet_en_20110.pdf
TOSHIBA BiCD Integrated Circuit Silicon Monolithic
TB62752AFUG
Step Up Type DC-DC Converter for White LED
The TB62752AFUG is a high efficient Step-Up Type DC-DC Converter specially designed for constant current driving of White LED.
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.
Features
- 2-8 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, IF = 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 34.5 V (MIN).
- IC package: SSOP6-P-0.95B
- Switching frequency: 1.0 MHz (typ.)
Pin Assignment (top view)
Note: This IC could be destroyed in some case if amounted in 180° inverse direction. Please be careful about IC direction in mounting.
Block Diagram
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. |
| 2 | OVD | 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. |
| 3 | VIN | Supply voltage input terminal. (2.8 V to 5.5 V) |
| 4 | SW | Switch terminal for DC-DC converter. Nch MOSFET built-In. |
| 5 | GND | Ground terminal. |
| 6 | FB | LED I F setting resistor connecting terminal. |
Table Caption: This table lists the pin configuration for an integrated circuit, detailing each pin's number, symbol, and function description, which includes enable/disable, over-voltage detection, power supply input, DC-DC converter switch, ground, and LED current setting.
I/O Equivalent Pin Circuits
1. SHDN
3. VIN to GND
-
FB
-
OVD
-
SW
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 34.5 V (MIN), Nch MOSFET switching operation is disabled in the IC. When the voltage of OVD terminal drops below 34.5 V (MIN), Nch MOSFET switching operation becomes available again.
If load of LED is detached, Nch MOSFET switching operation is disabled with detection of boost circuit voltage and the IC is protected from unexpected over voltage.
Setting of Capacitor
The recommended values are
C1 = 2.2 ( μ F) or more, C2 = 1.0 ( μ F) or moreThe 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 RSENS pin and GND.
The average current is set by this RSENS value and average current are obtained by the following equation.
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 | Indictor Size | Note |
|---|---|---|
| 2 to 5 | 10 μ H | LED current I F = 20 mA |
| Over 6 | 22 μ H |
Table Caption: This table specifies the recommended inductance values for LEDs based on the number of LEDs used. For two to five LEDs, a 10 μH inductor is suggested, while for over six LEDs, a 22 μH inductor is recommended, with a constant LED forward current of 20 mA in both cases.
Current Dimming Control
Recommended brightness control circuits are 4 types.
- (1) Input PWM signal to SHDN terminal
IF 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 C2 of charge depends on the constant number. And so, the actual IF 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 C2, arises in turning on. Take care in selecting the condenser.
- <<Current value in control with PWM: Ideal equation>>
<<Recommended application>>
- (2) Input analog voltage to FB terminal
IF can be adjusted with analog voltage input to FB terminal.
This method is without repeating IC ON/OFF, and no need to consider holding rash current.
[Notice]
- LED current value goes over 100% of the current set with RSENS, if the input analog voltage is between 0 to 300 mV (typ.).
<<Recommended application>>
- (3) Input PWM signal with filtering to FB terminal
IF can be adjusted with filtering PWM signal using RC filter indicated in recommended circuit, because the PWM signal can be regard as analog voltage after filtering.
This method is without repeating IC ON/OFF, and no need to consider holding rash current.
[Notice]
- LED current value goes over 100% of the current set with RSENS, if the input voltage after filtering is between 0 to 300 mV (typ.).
<<Recommended application>>
(4) Input logic signal
IF can be adjusted with logic signal input as indicated in recommended circuit.
The resistor connected the ON-State
