RT3612EB datasheet(30/47 Pages) RICHTEK

30 / 47 page

RT3612EB

DS3612EB-02 December 2019

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 15. Switching Frequency and Current with

Different VID

Controller internally control

TON adaptive to variable VIN

1.8

VID

Current

Ripple

1.8

VID

VIN=19V

VIN=12V

VIN=19V

VIN=12V

Frequency

The switching frequency can be derived from TON as shown

below. The losses in the main power stage and driver

characteristics are considered.



ONLS max

ONHS max

ONLS max

ONVAR

VID

DCR

N R

Freq







 



































VID : VID voltage

VIN : input voltage

ICC : loading current

N : total phase number

RONLS,max : maximum equivalent low-side RDS(ON)

nHS: number of high-side MOSFETs

RONHS,max : maximum equivalent high-side RDS(ON)

nLS : number of low-side MOSFETs.

TD : summation of the high-side MOSFET delay time and

rising time

TONVAR : TON variation value

DCR : inductor DCR

RLL : loadline setting (

Ω).

Although TON is designed for constant frequency target

while VID

≥ 1.8, the actual frequency is still impacted by

main power stage's loss and driver dead time. The

switching frequency rises as loading current increases.

Recommend to design the switching frequency based on

the optimized efficiency and thermal performance at thermal

design current (ICCTDC). For example, at ICC = ICCTDC, VID

= 1.8V and VIN = 19V, the switching frequency is 850kHz.

Then substitute these values into equations to get TON

and relative kTON.

Richtek provides a Microsoft Excel-based design tool to

help design RTON and kTON setting for the desired switching

frequency at TDC.

Table 9. PIN-SETTING of TONSET

TONSET[3:0]

KTON

0000

0.64

0001

0.73

0010

0.82

0011

0.91

0100

0101

1.09

0110

1.18

0111

1.27

1000

1.36

1001

1.45

1010

1.64

1011

1.82

1100

2.09

1101

2.36

1110

2.55

1111

2.91

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