RRAMP =

VCC ± 0.5V + VRAMP

25 2A - IOS

RAMP

VCC

CRAMP

RRAMP

RRAMP =

VCC - VRAMP

IOS - 25 2A

VRAMP =

((VIN ± VOUT) x gm + IOS) x T

VOUT

VIN

CRAMP

x

RS =

VCS(TH)

IOUT +

VOUT x T

L

CRAMP =

IOS x L

VOUT x A x RS

CRAMP =

gm x L

A x RS

x 1 +

5 - VOUT

VIN(MIN)

RS =

VCS(TH)

IOUT -

VOUT x T

2 x L

+

1 -

VOUT

VIN(MIN)

VOUT x T

L

x

CRAMP =

gm x L

A x RS

x 1 +

5 - VOUT

VIN(MAX)

RS =

VCS(TH)

IOUT -

VOUT x T

2 x L

x

+

1 -

VOUT

VIN(MIN)

VOUT x T

L

1 +

5 - VOUT

VIN(MAX)

1 +

5 - VOUT

VIN(MIN)

x

LM5116-HT

SLVSBS8B – OCTOBER 2013 – REVISED JANUARY 2014

www.ti.com

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General Method for 5 V < VOUT < 7.5 V:

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Best Performance Method:

This minimizes the current limit deviation due to changes in line voltage, while maintaining near optimal slope

compensation.

Calculate optimal slope current, IOS = (VOUT / 3) x 10 µA/V. For example, at VOUT = 7.5 V, IOS = 25 µA.

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Calculate VRAMP at the nominal input voltage.

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For VOUT > 7.5 V, install a resistor from the RAMP pin to VCC.

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Figure 15. RRAMP to VCC for VOUT > 7.5 V

For VOUT < 7.5 V, a negative VCC is required. This can be made with a simple charge pump from the LO gate

output. Install a resistor from the RAMP pin to the negative VCC.

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26

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