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LM3409HV-Q1 Input Offset on High Side Sense Comparator

Other Parts Discussed in Thread: LM3409HV, TINA-TI


Dear, Sir.

I am still waiting for your advice.

Below is my personal assumption after checking all datasheet contents.

Can you accept that,?

Otherwise, Please corrent if there were any miss-understandings.

1. Datasheet defines Vcst under Vadj=Vadj-oc(open connection?).

    typ = 246mV.

   According design procedure, 248mVwill be ideal value.

   Hence,I guess 2mV(+- 2mV) could be the offset under 25 deg.C.

2. +- 15mV is a kind of Vcst spec under all temp range(-40 ~ +125deg.C)

   and it would be denpended on the offset.

   I guss 150uV/deg.C could be the thermal coefficient of the offset.

   15mV/(125deg.C - 25deg.C) = 0.15mV/deg.C


Best Regards,

H. Sakai


Dear, Sir.

I am very sorry that my explanation was too poor on previous mail.

Vin=50V for LM3409HV is supplied from DCDC converter circuit.
My customer is set on bypass switch on half position of LED's
series.Hence, Vo would be changed at the switch ON/OFF.

The customer would like to select smaller Co as 0.01uF and smaller
L to reduce the cost.

1)Delta IL-pp would become large at Vo was increased due to switch
  OFF(increased LED series count double).
2)Looks like Vcst was affected with comparator offset and peak
  current control(IL-max).

The customer worry about LED brightness waving due to out of
regulation of this device at above loading condtion change.

These are the background of my previous questions.
I am hoping to get your understanding and help at this time.

My private mail ADRS is;
Please contact immediately if it was better for us.

Best Regards,
H. Sakai


Dear, Sir. 

High side sense comparator is embed into LM3409HV for avaraging og ILED. 

My customer's questions are relating that. 

Please give your advice. 

1. TINA-TI Transient Model. 

  We can observe the ripple of ILED output current. 

 Does it mean the model is including such comparator's offset behavior?

2. Spec of the Offset on comparator. 

a) Can you specify the offset such as typ & max based on IL-MAX-L & IL-MAX-H

    or based on another parameter under room temp?

b) Can you specify the thermal coefficient of above offset? 

Best Regards, 

H. Sakai