LM5116: UVLO Divider Calculation

HI

1 can you confirm you caculation result?

2. Vstart in TPS54561 is still EN threshold or converter start to work votlage which is close to Vinmin, Vinmax in LM5116 means the max input votlage. the current go through Ruv2 should be less than 2mA.  as the the UVLO pull down resistor value is typcial 80ohm , max 210ohm.

Thanks

yes, RUV1=1.215V*( 102k/( 6.6V + 5uA*102k - 1.215V ) ) = 21.02k.

But is Ruv2=102k calculated from RUV2 > 500 x VIN(MAX) ? how much is the VIN(MAX)?

HI Kingson:

when you design your power system with LM5116 , what is your system max input voltage?

Thanks

Hi 

Input Voltage Range: Typical 12V, from 7.0V(VINmin) to 60.0V(VINmax)

Thanks.

HI Kingson:

You can use 60V as VINMAX for Ruv2 calculation.

Thanks

Hi Daniel

If VINmax=60V,

then RUV2=500*60=30,000=30k, and RUV1=1.215V*( 30k/( 6.6V + 5uA*30k - 1.215V ) ) =60.9Ω ?

The UVLO Divider Calculation of LM5116 is different from TPS54561, so I'm a little confused with it...

Hi Daniel

Input Voltage Range: Typical 12V, from 7.0V(VINmin) to 60.0V(VINmax)

Ruv2=30k, Ruv1=6.65k (standard resistance close to 6.585k)

With these conditions, how to get the UVLO stop voltage and start voltage? Because the calculation of Ruv2 and Ruv1 did not use Vstop and Vstart.

HI

the UVLO hysteresis is fixed in LM5116 , see blow spec. so you start up is 6.88V, stop voltage is 6.14V.

Thanks

Hi Daniel

Sorry, but could you explain in detail or by formula that how to get the start voltage 6.88V and stop voltage 6.14V?

Hi

When voltage on EN higher than 1.25V, the controller will start to work, when it lower than 1.125, it will stop working. Using 30K and 6.65K for divide caculation. 

7.3.2 Enable : If the enable pin is pulled below 0.5 V, the regulator enters shutdown, drawing less than 10 μA from the VIN pin. Raising the EN input above 3.3 V returns the regulator to normal operation.

7.3.3 UVLO : If the UVLO pin is pulled below 1.215 V, the regulator enters a standby mode of operation with the soft-start capacitor discharged and outputs disabled, but with the VCC regulator running. If the UVLO input is pulled above 1.215 V, the controller will resume normal operation.

30k and 6.65k are UVLO divide resistance. I cann't find the relation between EN pin and 1.25V or 1.125V...