TPS92515HV: Reduced for startup time

ACGUY

Part Number: TPS92515HV

Hello E2E,

Our using EVM has about 2.5-msec startup time.
Conditions are follows;
- Vin is 24V.
- LEDs are 5 pieces in series. Vf = 3.05V/piece.
- ILED is 500mA.

At dumming from PWM-port, we want to reduce the startup time. I think that if prebias input for Vcc and IADJ that startup time to be early.

Question;
1) When Vin is not input, can I input 5V to Vcc?
2) When Vin input and PWM input Low, can I input 5V to Vcc and any voltage input to IADJ?

Regards,
ACGUY

over 6 years ago

0 Irwin Nederbragt over 6 years ago

TI__Mastermind 28655 points

Hello ACGUY,

VCC can be applied external however absmax is 5.5V so it needs to be below this. VCC maximum is 5.2V which doesn't leave much room to do this. Voltage can be applied to Viadj and also needs to be within the absmax limits.

I would look at what is causing the turn-on delay with an oscilloscope.

Best Regards,

0 ACGUY over 6 years ago in reply to Irwin Nederbragt

Guru 11170 points

Hello Irwin,

Thank you for reply.
Currently, IADJ-port is pulled-up to Vcc. When input on PWM-port to Low, Vcc to be descend, therefor rise up speed of IADJ voltage is to be slow down.

This device rise up speed is very fast on WEBENCH.

Using LED is "GW CS8PM1.EM-LQLS-A333-1(OSRAM)".

We looking for how to speed up for start up time.

Regards,
ACGUY

WebenchReports PWM dimming.pdf

LED start up.pdf

0 Irwin Nederbragt over 6 years ago in reply to ACGUY

TI__Mastermind 28655 points

Hello ACGUY,

Vcc should not be descending when PWM is low. If Vcc is low the part will not run. Vcc has an UVLO circuit. If Vin is applied Vcc should be present. Another thing that can cause delay is boot UVLO. If the boot capacitor discharges it has to recharge before it can run, this is explained in the datasheet.

Best Regards,

0 ACGUY over 6 years ago in reply to Irwin Nederbragt

Guru 11170 points

Hello irwin,

I ran to simulation for transient operation on Webench. I set customized LED. TPS92515HV has very fast response. However, EVM of ours is slow.
Does Webench not consider discharge of boot capacitor?

Regards,
ACGUY

0 Irwin Nederbragt over 6 years ago in reply to ACGUY

TI__Mastermind 28655 points

Hello ACGUY,

Iadj on the EVM has a 0.1 uF capacitor which will cause a delay. Try reducing this value.

Best Regards,

0 ACGUY over 6 years ago in reply to Irwin Nederbragt

Guru 11170 points

Hello Irwin,

I will try various techniques.

Thanks,
ACGUY

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TPS92515HV: Reduced for startup time