TPS568215: Mode Pin Resistor Settings

HI Lishuang

What is the tolerance of Mode Pin?

Suppose we choose RM_L 20K and RM_H 120k
Light Load Operation=FCCM, Current Limit=ILIM, Frequency (kHz)=800HZ
What is the range of RM_H?
RM_H min=?? typ=120k max=?

HI Lishuang

Thank you very much for answering

Why is it in TPS568215 datasheet 7.3.4 MODE Selection
It is recommended to choose 5% resistance, as follows
A guideline for the top resistor (RM_H) and the bottom resistor (RM_L) as 5% resistors is shown in Table 3

As long as one of (RM_H) or (RM_L)choose 1%, do you think there is no problem?

HI Lishuang

Suppose we choose RM_L  51K and RM_H 180k

internal LDO is 4.7V

Vmode=1.037V(TYP)

 +/-10% in all conditions.

Vmode=0.933V ~1.1407V

but  RM_L  51K and RM_H 200k

Vmode=0.954V(TYP)

HI Lishuang

Suppose we choose External Bias=5V

How to choose MODE?

Hi Aaron,

That has no effects on choosing Mode resistors. Internally this VREG5 is referenced to detect the MODE option. If external bias is added, it override the internal LDO and become VREG5 then.

Thanks.

Andrew

Hi Aaron,

You mean connect MODE to external 5V and this external 5V doesn't connect to VREG5?  We don't recommend this. Mode detection is controlled by internal VREG5. We strongly recommend to connect MODE to VREG5, not external connection.

Thanks,

Lishuang

HI  Lishuang and Andrew

Thank you very much for answering

I mainly ask 3 questions as follows

1.Why is it in TPS568215 datasheet 7.3.4 MODE Selection
   It is recommended to choose 5% resistance, as follows
   A guideline for the top resistor (RM_H) and the bottom resistor (RM_L) as 5% resistors is shown in Table 3

   As long as one of (RM_H) or (RM_L)choose 1%, do you think there is no problem?

2.Suppose we choose RM_L  51K and RM_H 180k 

  internal LDO is 4.7V

  Vmode=1.037V(TYP)

 +/-10% in all conditions.

 Vmode=0.933V ~1.1407V

 but  RM_L  51K and RM_H 200k

 Vmode=0.954V(TYP)

3.Suppose we choose External Bias=5V

   How to choose MODE?

https://www.ti.com/lit/an/slvae69/slvae69.pdf?ts=1624027073825&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS568215

Andrew, already answered

Additional question

4.May I know the ratio of vcc (VREG5) and mode resistance
   Range?

E.g
VCC*(0%~3%) Mode 1
VCC*(3%~8%) Mode 2
VCC*(8%~12%)Mode 3
VCC*(12%~18%)Mode 4
VCC*(18%~21%)Mode 5
VCC*(21%~25%)Mode 6
........

Hi Aaron,

1. For mode pin config, it's preferred to use high precision resistor. The words that you mentioned "A guideline for the top resistor (RM_H) and the bottom resistor (RM_L) as 5% resistors is shown in Table 3" can be understood as "the 5% resistors can be endured by following the recommended resistance value in Table 3".

2. Appreciate your effort for the analysis. There's a small error that %5 resistor cannot bring +/-10% variation for the mode pin voltage. Mode pin voltage is divided from VREG5, the ratio equals to RL/(RL+RH), that's 1/(1+RH/RL). So we could know larger RH/RL can cause smaller ratio. 

So the largest RH/RL in range is 180k*1.05/(51k*0.95)=3.9. With 4.7V VREG5, smallest mode pin voltage for this config is 0.959V. The smallest RH/RL in range is 180k*0.95/(51k*1.05)=3.193, largest mode pin voltage for this config is 1.12V. So the range should be 0.959~1.12V.

But I think maybe it's better not to think too much about the calculation here, since there could be other internal circuit affecting the mode pin voltage detection. I advise to just follow our datasheet recommendation to use the device.

4. Do you want to use other resistance value other the the recommended one? I recommend to follow the table in our datasheet. We can guarantee the performance just for the application following our datasheet's specs and guidelines.

Thanks,

Andrew

HI Andrew

1.TPS56C215. Is Mode Pin Resistor Acceptable 5% Resistor?

2.I am confused, RM_L=51k(5%) RM_H=180k(5%) range is 0.959~1.12V mode 6

But mode 5 is RM_L=51k(5%)   RM_H(5%)=200k   typ=0.9549V   MAX=1.033V
Why not choose the wrong mode by mistake

3.I need to analyze RM_L=51k(1%) RM_L=180k(5%) (MODE 6)
   The possibility of incorrect selection of RM_L=51K, RM_L=200k (MODE 5)

Thank you very much for answering

Hi Aaron,

Thanks for clarifying your requirement. Then I can understand why you ask those questions before.

Lishuang or me will check with IC designer next Monday and give you feedback.

Thanks,

Andrew

HI Andrew

Thank you very much for answering

I know that RM_L=51k(1%), RM_L=180k(5%), RM_L=51k(1%), RM_L=200k(5%) overlap,
But what I want to know is, mode resistance range(IC decide range )
E.g
5 mode 0.9V~0.99V
6 mode 0.99V~1.09V

Hi Aaron,

For 5 Mode (51K, 200K), 0.9-0.99V is okay.

For 6 mode (51K, 180K), 1.03-1.09V is okay.

Thanks,

Lishuang

HI Andrew and Lishuang

You may have misunderstood me

What I want to know is the range of IC

For example, Table 7-1 of TPS51397A datasheet. VOLTAGE ON MODE in MODE Pin Resistor Settings

(0~10%)*VCC        mode 1

(10%~20%)*VCC   mode 2

(20%~30%)*VCC   mode 3

(30%~50%)*VCC   mode 4

Thank you very much for answering

Hi Aaron,

Checked with design, we can get the value for Mode 5 and Mode 6 is as below.

For 5 Mode, (19%-21.5%)*VCC.

For 6 mode, (22.5%-24.5%)*VCC.

Overall, we strongly recommend to use mode table resistor value with 1% resolution.

Thanks,

Lishuang

HI  Lishuang

I recommend the data sheet
RM_L = 51K RM_H=180K mode 6
Need to be modified, ratio=0.220779221 is too low, I feel very confused
RM_L = 51K, RM_H=180K typ=(22%)*VCC. Not in (22.5%-24.5%)*VCC, range

Hi Aaron,

Really sorry for misunderstanding. I should correct my last response.

For 5 Mode, [(6/32)%-(7/32)%]*VCC, it is (18.75%-21.875%)*VCC.

For 6 mode, [(7/32)%-(8/32)%]*VCC, it is (21.875%-25%)*VCC.

There is a same range in the middle, so we need to leave some margin for 21.875%. For example, (18.75%-21.5%)*VCC for mode 5 and (21.9%-25%)*VCC for mode 6.

Thanks,

Lishuang

HI  Lishuang

I still feel very confused，RM_L = 51K(1%), RM_H=180K(1%)

RM_L = 50.49K (min), RM_H=181.8K(max)

For 6 mode  [21.7%(min)]*VCC，Still can't reach (21.875%-25%)*VCC.

HI  Lishuang

1.tps568215 and tps56c215
   mode Mode, (range%)*Is VCC the same?

2.RM_L=51k, RM_H=150k   [25%(typ)]*VCC

Is it recommended to modify (resistor)

3.  RM_L=51k, RM_H=150k  7 mode

Mode Mode, is (range%) 25%~28.125%?

4.RM_L=51k(1%), RM_H=180k(1%)   6 mode

I want to modify it to RM_H=174k(1%), is it possible?

5.Can you provide a range of 1~12 mode?

Thank you very much for answering

Hi Aaron,

Please send me an email~~~lishuang_zhao@ti.com

Thanks,

Lishuang

HI  Lishuang

OK