2.2 Setup
(1)
Duty Cycle C15(nF) 0.0875
C15(nF) C9(nF) 0.175
(2)
AvgPower R7I2flash R7DI2noflashR7(1 D)
(3)
AvgPowerLED IflashVFLEDDInoflashVFLED(1 D)
(4)
Setup
2.2.1 EVM Factory Configuration
The EVM is configured to provide the following nominal operating conditions:•Movie light current: 200 mA•Flash current: 700 mA•Precharge current: 42 mA•Length of flash: 320 ms•Time between flashes: 3.2 s
2.2.2 Changing Flash Timing
The length of flash and time between flashes can be changed by changing capacitors C15 and C9.Capacitor C15 sets the length of the flash, and capacitor C9 sets the time between flashes. The time ofeach period can be calculated, in seconds, using Equation 1 where C(nF) is the value of thecorresponding timing capacitor in nanoFarads.
For example, the EVM has a 0.056- µF capacitor installed for C15 which determines the length of the flash.Using Equation 1 , a 0.056- µF capacitor provides a 320-ms flash.
Care must be taken when changing the timing so that the maximum power rating of the LED (D1) orsense resistor (R7) are not exceeded. The average power of these components can be calculated usingthe duty cycle of the flash circuit. The flash duty cycle is the time the LED is in flash mode divided by thesum of the flash mode and time between flashes. The duty cycle can be calculated using Equation 2 withthe value of the timing capacitors C15 and C9.
The average power dissipated in the sense resistor R7 is calculated using Equation 3 . In Equation 3 , I
flashis the flash current level, and I
noflash
is the current when not flashing which is zero or the torch currentvalue depending on the setting of JP1.
The average power dissipated in the LED is calculated using Equation 4 . In Equation 4 , V
FLED
is theforward voltage of the LED, I
flash
is the flash current level, and I
noflash
is the current when not flashing whichis zero or the torch current value depending on the setting of JP1.
2.2.3 Using External Control
The EVM has provisions to disable the onboard timing circuit and use an external controller. An externalcontroller can be connected to connector J3 to drive the enable and flash inputs of the TPS6105x.Resistors R11 and R12 should be removed and left open on the EVM to avoid signal contention betweenthe onboard timing circuit and the external controller.
2.2.4 Operation
1. Configure JP1 to enable or disable torch mode as desired.2. Connect the input voltage return to J2.3. Connect the positive input voltage to J1.4. Turn on input voltage. If JP1 is shorted, then the LED turns on in torch mode. If JP1 is open, the LEDremains off.5. Push the FLASH button to flash the LED.6. The LED flashes for approximately 320 ms.7. If JP1 is shorted, then the LED returns to torch mode. If JP1 is open, the LED turns off.
SLVU150 – January 2006 TPS61059EVM-141 3
