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# [FAQ] TPS92633-Q1: How to design with CERA(TPS92633-Q1) in five minutes?

Part Number: TPS92633-Q1

Hi team,

1. What are the prominent features of TPS92633-Q1?
2. How can the external resistor components of the TPS92633-Q1 be designed?
3. What should I pay attention to during layout (designing diodes and capacitors)?
4. If OUT3 is not used, is it no problem to left IN3, RES3 and OUT3 open?
• Hi,

1. 1) Off-board LED Driving Solution:
• TPS92633-Q1 is designed to support off-board binning resistor with robust EMC immunity, so it has superior advantage over Bar/QR-code solution for it reduces the effort of corresponding during manufacturing. With off-board binning resistor, one output current corresponds to one R(ICTRL2) on the LED board.
• 2) External Shunt Resistor for Thermal Sharing:

• When supply voltage is going higher and higher than LED required forward voltage, the current path will change from Iout to Ires gradually. The shunt resistor starts to share the voltage drop between supply and LED. In result, some amount of power is dissipated by shunt resistor.
• This feature will be preserved for the whole Cera family (e.g. TPS92623-Q1 and TPS92624-Q1).
1. You can refer to https://www.ti.com/lit/zip/slvrbh1  for the calculation of external component. In this tool, grey box is fixed value, while yellow is your setting and blue is the calculated value.

Step 1: Set current. Choose from ‘Current Setup(no off-board bin)’ to‘Current Setup(off-board bin)’ according to situation. R(IREF), R(ICTRL) and R(SNSx) can be decided here.

Step 2: Set R(RESx) using the equation (1) first.

(1)

It should be noted that the basic principle is to design the R(RESx) to consume appropriate 50% total power dissipation at typical supply operating voltage.  P(RES)=0.5P(device).

So Equation(1) is derived from R(RESx)*I(RESx)^2=0.5*(V(SUPPLY)-V(OUTx))*I(OUTx_Tot). Here, I(RESx)≈I(OUTx_tot) for Ratio of RESx current to total current is nearly 1.

And then use the calculation tool to type in the ‘RES resistor’ sheet to see the calculated Pres(mW) curve accordingly. Usually considering the high Pres(mW), the package of R(RESx) needs to be carefully selected among power resistors.

Step 3: In ‘Single LED Short Threshold’ sheet, type in the R(IREF) and single short detection threshold, and then R(SLS_REF) is decided. If not used, connect SLS pin to grond.

Step 4: ‘PWM and DIAGEN Threshold’ sheet can decide the voltage divider resistance on ‘PWM’ and ‘DIAGEN’ pin.

Step 5: For multiple devices'  ‘One-fails-all-fail’ function: If MCU is used, the 20k pull-up resistor is used with a zener diode on the fault pin to MCU GPIO to make fault pin voltage compatible with the MCU GPIO digital logic and protect the MCU GPIO. If no MCU is used, all fault pins can be connected together.

1. Apart from the layout guidelines on datasheet, please refer to https://www.ti.com/lit/pdf/slvaem8 to achieve high BCI (Bulk Current Injection) immunity performance. Also, the TPS92633Q1 EVM user's guide can also be referred to.
1. Connect PWM3 to the ground, and  then it's OK. Please don’t make PWM pin floating at any time.