2

COND(QH2)

OUT

DSON(QH2)

P

I

R

˜

2

OUT

COND(QL1)

OUT

DSON(QL1)

IN

V

P

1

I

R

V

§

·

˜

˜

¨

¸

©

¹

SW(QH1)

IN

OUT

r

f

sw

1

P

V

I

t

t

F

2

˜

˜

˜

˜

2

OUT

COND(QH1)

OUT

DSON(QH1)

IN

V

P

I

R

V

§

·

˜

˜

¨

¸

©

¹

2

OUT

COND(QH1)

OUT

DSON(QH1)

IN

V

P

I

R

V

§

·

˜

˜

¨

¸

©

¹

DITH

MOD

10 A

C

F

0.24 V

P

u

u

SS

REF

ss

SS

C

V

t

I

24

LM5176

SNVSAI1A – JUNE 2017 – REVISED MARCH 2019

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Product Folder Links: LM5176

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Copyright © 2017–2019, Texas Instruments Incorporated

8.2.2.10 Soft-Start Capacitor

time is given by:

(28)

8.2.2.11 Dither Capacitor

The dither capacitor sets the modulation frequency of the frequency dithering around the nominal switching

modulation frequency.

(29)

For the current design dithering is not being implemented. Therefore a 0

Ω resistor from the DITH pin to AGND

disables this feature.

8.2.2.12 MOSFETs QH1 and QL1

The input side MOSFETs QH1 and QL1 need to withstand the maximum input voltage of 50 V. In addition they

must withstand the transient spikes at SW1 during switching. Therefore QH1 and QL1 should be rated for 60 V

or higher. The gate plateau voltages of the MOSFETs should be smaller than the minimum input voltage of the

converter, otherwise the MOSFETs may not fully enhance during startup or overload conditions.

The power loss in QH1 in the boost mode of operation is approximated by:

(30)

The power loss in QH1 in the buck mode of operation consists of both conduction and switching loss

components given by Equation 31 and Equation 32 respectively:

(31)

(32)

switching loss).

The power loss in QL1 in the buck mode of operation is shown in Equation 33:

(33)

8.2.2.13 MOSFETs QH2 and QL2

The output side MOSFETs QH2 and QL2 see the output voltage of 12 V and additional transient spikes at SW2

during switching. Therefore QH2 and QL2 should be rated for 20 V or more. The gate plateau voltages of the

MOSFETs should be smaller than the minimum input voltage of the converter, otherwise the MOSFETs may not

fully enhance during startup or overload conditions.

The power loss in QH2 in the buck mode of operation is approximated by:

(34)

The power loss in QL2 in the boost mode of operation consists of both conduction and switching loss

components given by Equation 35 and Equation 36 respectively: