TLD5541-1QV Datasheet, PDF (28/82 Pages) Infineon Technologies AG – H-Bridge DC/DC Controller with SPI Interface

H-Bridge DC/DC Controller with SPI Interface
TLD5541-1QV
Regulator Description
The F.D. operation consists of discharging the capacitor C_OUT to the final load voltage (Figure 15-B) before the
bypass switch closure. During this fast discharge phase, all the LEDs are off. The external Microcontroller
Software has to take care of the synchronization between the TLD5541-1QV F.D. operation and the bypass
Switches activation.
The discharged energy from C_OUT is recovered back to the Input capacitor C_IN which could cause a small
overshoot on the C_IN itself. This feature allows high efficiency designs also when PWM operation with repetitive
Load Jumps is needed.
The F.D. feature is needed when a negative V_OUT step is performed, so when one or more LED functions are
switched off. If additional LED functions are turned on, increasing the output voltage, the F.D. does not have to be
used. In MFS topologies, a short interruption of the current is observed during the Load Transitions (either positive
or negative) in all the functions, until V_OUT is stable and the device control loop is able to provide the target output
current.
We will refer to any Voltage-Current or Load configuration just before the Load Jump as "Initial" (Figure 15-A),
while we will refer to any value after the system is in the new Load configuration as "Final" (Figure 15-C).
Set the Target Cout discharge voltage
The Target output voltage (V_OUTFinal) of an F.D. operation is communicated to the TLD5541-1QV as a fraction of
the V_OUT at the beginning of the Jump (V_OUTInitial), and not as an absolute Value.
In order to quickly discharge the output Capacitor to a desired Ratio of the initial voltage, two SPI commands have
to be sent to the TLD5541-1QV register MFSSETUP1.
• The first is to write in the MFSSETUP1.LEDCHAIN the Ratio Denominator
• The second is to write in the MFSSETUP1 register the Ratio Numerator and the Start Of Multi Floating Switch,
respectively in the LEDCHAIN and SOMFS bitfields
After the second command, as soon as the Chip select is raised the F.D. begins. The final output voltage of the
F.D. operation, after a MFS routine is correctly performed, will be approximately:
V_OUTFinal
=
RatioNumer ator
RatioDenom inator
⋅V_OUTInitial
(4)
The MFSSETUP1.LEDCHAIN registers sets both the LED Ratio during F.D and the short circuit threshold. For this
reason both the correct V_OUT Ratio and correct short circuit protection voltage have to be set according to the LED
Load. See Table 10 for reference.
To have the correct short circuit protection on a F.D. operation, the first LEDCHAIN value sent via SPI (Ratio
Denominator), should also guarantee an adequate short circuit detection for the Initial Load. The second
LEDCHAIN value (Ratio Numerator + SOMFS) should guarantee correct Short circuit detection for the Final Load.
For more information about short circuit protection, see Chapter 10.2.1.
Example:
If the VFB voltage divider for the Short circuit detection is set like in Table 10.
In order to jump from 6LED(18V) to 2LEDs (6V), the Ratio is 1/3 of initial voltage.
So the 2 SPI commands that have to be sent are:
Spi command 1: set MFSSETUP1 to 0x06 (Ratio Denominator = 6, V_{Short_LED} = 16.8V)
Spi command 2: set MFSSETUP1 to 0x12 (Ratio Numerator+SOMFS = 0x02+0x10, V_{Short_LED}= 4.6V )
Preparation time t_prep:
The TLD5541-1QV enables the user to set a delay between the beginning of the Load Jump and the moment in
which the switching activity will restart to provide output current. This delay is needed to safely close the bypass
Data Sheet
28
Rev. 1.0, 2016-05-20