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TPS61089: VOUT definition

Hirokazu Takahashi

Expert 8420 points

Part Number: TPS61089

Hello Support team,

Could you please support below my question?

Q1. VOUT is defined as 12.6V@Max in TPS61089 datasheet p4. Recommended Operating Conditions.
Is this value at PWM mode?, In case of PFM mode, VOUT is increased 1% than PWM according to datasheet. Should we keep 12.6V at PFM mode?

Q2. VOUT is set by external resistance, R1 and R2. Even if we set both resistance to keep 12.6V, VOUT will be over 12.6V in case of maximum value of VREF as 12.236V.

Q3. Should we set R1 and R2 to keep VOUT less than 12.6V?
VOUT of Absolute Maximum is defined as 14.5V. Can we set Max of VOUT as 12.6~14.5V? What problem will be occurred at that condition?

Q4. If VOUT is less than VIN, what problem will be occurred?

Best Regards,
Hirokazu Takahashi

over 6 years ago

0 Helen chen over 6 years ago

TI__Mastermind 40080 points

Dear Sir,

Why you want to set Vout at 12.6V, so margin? suggest you set the center Vout at 12.2V or so to make sure the Vo_max is lower than 12.6V.

Actually, most of the customer set the Vout at 12V.

For the TPS61089, when Vo higher than 12.7V, it may enter into OVP.

0 Hirokazu Takahashi over 6 years ago in reply to Helen chen

TI__Expert 8420 points

Hello Helen-san

Thanks for reaching out.

We are concerning about ripple and over/under shoot at load transient.
Could you let me know the phenomenon at the case VOUT is less than VIN also?

Regards,
Hirokazu

0 Helen chen over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 40080 points

Dear Sir,

What is your Vin?

When Vo is lower than Vin, it will be clamped at Vin-0.5V, 0.5V is the body diode voltage drop.

0 Hirokazu Takahashi over 6 years ago in reply to Helen chen

TI__Expert 8420 points

Hello Helen-san

Thanks for your support.
Vin = 9.5V@max

Regards,
Hirokazu Takahashi

0 Helen chen over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 40080 points

Dear Sir ,

By proper design, even in the load dynamic condition, the Vout will not drop below Vin.

What will be the load change during the load dynamic condition?

0 Hirokazu Takahashi over 6 years ago in reply to Helen chen

TI__Expert 8420 points

Hello Helen-san

Thanks for your reply.
The load is the driver for actuator.
The load current goes from 0A to 1.0A and from 1.0A to 0.0A.

Best Regards,
Hirokazu Takahashi

0 Helen chen over 6 years ago in reply to Hirokazu Takahashi

TI__Mastermind 40080 points

Dear Sir,

For the 0-1A load dynamic, by proper compensation value, and use enough Cout, the output voltage will not drop below Vin. it should be OK!