LM25118 OCP功能

Johnson Chuang

Prodigy 126 points

Other Parts Discussed in Thread: LM25118

目前設計是照DEMO的線路來作,關於這顆POWER IC有以下幾點問題:

1.想請教一下關於LM25118這顆POWER IC是否有OCP的功能?

2.如果有OCP,那麼OCP應該如何計計?

3.在SPEC上所求的Iripple以及Ipk是對電感端的電流,還是輸出IOUT就是照那部分所寫的使用?

關於這幾點麻煩當忙解答,謝謝.

LM5118-tk.pdf

13 年多前

0 Nick Liu 13 年多前

TI__Prodigy 180 points

LM25118是一顆寬電壓buck-boost 電源控制晶片

1. Yes, LM25118 has OCP

2. The OCP level will be set by the resistor between pin CS and CSG. Details of calculation can be followed by the equation in page 20 of the datasheet(R13 calculation).

3. The Ipk and Iripple refer to Inductor current(電感電流)

祝設計順利

0 Johnson Chuang 13 年多前回复 Nick Liu

Prodigy 126 points

sorry, page 20沒有看到你說的R13 calculation,你說的是在Page17 R13的calculation?

那當我計算完我的R13使用如DEMO相同,那我的OCP就會等於IPK- (Buck)and IPK+(Buck-Boost)?

還是說CS and CSG 有Voltage/R(R13)就能計算出準確的OCP??

0 Johnson Chuang 13 年多前回复 Nick Liu

Prodigy 126 points

補充

我知道是使用CS and CSG的R來控制,但是我需要知道更精確能夠直接知道OCP發生點,及設定方式.

假設我需要OCP再6A發生,並且shutdown,那我該如何去set OCP的值?

0 Nick Liu 13 年多前回复 Johnson Chuang

TI__Prodigy 180 points

We may have different versions of datasheet or pdf format, yes, pls refer to R13 calculation in LM25118 datasheet.

請注意LM25118的OCP是PEAK current mode.

同時因為LM25118有buck mode 和 buck boost mode 因此Ipk 皆需計算取較大值已確保電流輸出

另要注意的是在buck boost mode 時 current limit threshold 會自動設定為2倍

0 Nick Liu 13 年多前回复 Johnson Chuang

TI__Prodigy 180 points

首先需確認你的6A是continued load current 還是peak Inductor current.

假設是continued load current(Iout) 則請依照equation 10 至 equation 13 即可計算出所需R值

請注意 LM25118 的 OCP 是 Hiccup mode 而不是shut down. 優點是過流解除就會自動回復

0 Johnson Chuang 13 年多前回复 Nick Liu

Prodigy 126 points

所以在buck boost mode情況下,我的Ipk current計算為9.5A,MAX load Iout=3A,經過他的自動設定,Ipk current threshold 就會變成19A,也就OCP=19A是嗎?

或者是OCP=IOUT(1+VOUT/VIN) =3*(1+12/5)=10.2A這公式計算出來的?

Thanks.

0 Johnson Chuang 13 年多前回复 Nick Liu

Prodigy 126 points

1.假設是在 peak inductor current(OCP)=6A(buck-boost mode) vin=9 vout=12,

equation:6=Iout(1+12/9)→Iout=2.6A? 是嗎??

2.set CCM Iout=3A calculation R=25m ohm Ipk=10A(Buck-Boost mode) so OCP=Ipk(Buck-Boost mode)=10A or

OCP=auto double Ipk=20A?

Thanks.

0 Nick Liu 13 年多前回复 Johnson Chuang

TI__Prodigy 180 points

若buckboost mode Ipeak 為9.5A,

則依據equation 13, R13=2.5V/(10*Ipeak)=26mohm

0 Nick Liu 13 年多前回复 Johnson Chuang

TI__Prodigy 180 points

1. 通常在設計上我會用Iout去推算出Ipeak意以用來設定peak current limit

2. Don't be confused bu the double limit, when you set Ipeak for buckboost mode then it follows your setting. when calculating R13, if use buck mode Ipeak the reference voltage is 1.25V and when you use buckboost mode the reference volatge is 2.5V. Pls refer to equation 12 and 13.

0 Johnson Chuang 13 年多前回复 Nick Liu

Prodigy 126 points

But double peak current limit can cause L1 bad

so CCm Iout=3A計算出R=26m ohm Ipk=9.5A(buck-boost mode)

那Ipk=9.5A就是OCP還是需要再double變成19A才算OCP?

0 Nick Liu 13 年多前回复 Johnson Chuang

TI__Prodigy 180 points

When you calculate R13 based on buckboost current with reference voltage of 2.5V

the Ipk OCP under buckboost mode will be just as what you set(in this case 9.5A).

Only if you calculate based on buck mode Ipk with reference voltage of 1.25V, the OCP under buckboost mode will be double to what it is under buck mode. Hope this help.

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LM25118 OCP功能