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TL432B-Q1: Build LDO with TL432, high output ripple

Part Number: TL432B-Q1

Hi expert,

My customer build LDO with TL432 in their automotive application and has ripple issue.

1. Test condition

(1) Build LDO circuity as shown in figure one

Figure 1

(2)Vin=6~7V, Vo=5V, Iout = 0~300mA

(3) R1=R2=Rfb, Imin=1 mA。

(4)NPN transistor has below characteristics

Figure 3

(5)Vin is supplied with DC source and digital load is in CC mode

2. Problem in testing

During testing, we fund different load condition and input voltage will cause large variation in output ripple. When decrease the resistance value of R3, output ripple becoming even larger. When empty load, Vout is 5V and no output ripple. Output ripple seems increase with load current. But, when load goes to heavy, ripple will drop again.

3. Testing results

(R1=R2=1k; R3=500Ω, CC load)

Vin/V

Io/A

Vo/V

ΔVo/mV

6

0.1

4.98

92

6.5

0.1

4.97

265

0.3

4.95

200

7

0.1

5.00

311

0.3

4.94

415

PS: Vo are all measured on digital load, actual LDO output is 0.01 to 0.02V high thean measured.

(R1=R2=1k; R3=333Ω, CC load)

Vin/V

Io/A

Vo/V

ΔVo/mV

6

0.1

4.98

146

6.5

0.1

4.99

285

0.3

4.94

366

7

0.1

5.00

313

0.3

4.96

499

PS: Vo are all measured on digital load, actual LDO output is 0.01 to 0.02V high thean measured.

(R1=R2=1k; R3=200Ω, CC load)

Vin/V

Io/A

Vo/V

ΔVo/mV

6

0.1

4.97

226

6.5

0.1

5.00

301

0.3

4.95

467

7

0.1

4.97

226

0.3

4.97

87

PS: Vo are all measured on digital load, actual LDO output is 0.01 to 0.02V high thean measured.

 

One waveform sample:

R1=R2=1k; R3=500Ω; Vin=6.5V, Io=0.1A; ΔVo=265mV

Thanks!

Sheldon

  • Hi Sheldon,

    This oscillation is occurring because seemingly the phase margin is low. You should be able to correct this by adding a capacitor between the cathode and reference.

    Second, probe your cathode pin and I think you won't have enough input voltage so you need a lower cathode current requirement.

    I suggest using a ATL432LI-Q1 here to reduce the need for a higher cathode current. This should resolve oscillation issues for this issue as well.

    Thanks,

    Abhinav.