RT6310ASLASHAH datasheet(11/54 Pages) RICHTEK

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RT6310

is a registered trademark of Richtek Technology Corporation.

DS6310-04

August 2023

www.richtek.com

of regulating voltage, the next one-shot on-time timer is

activated. On the contrary, when the output current

increases from light load to heavy load and inductor

current finally reaches to the continuous conduction, the

switching frequency smoothly increases to preset value.

The boundary load condition between continuous

conduction and discontinuous conduction mode is

shown in Figure 2 and is calculated as follows :

OUT

LOAD

−



where ILOAD is the output loading current and tON is the

on-time

Slope = (VIN - VOUT) / L

IPEAK

ILOAD = IPEAK / 2

tON

Figure 2. Boundary Condition of CCM/DEM

As mentioned above, diode emulation mode features

natural high efficiency in the light-load conditions. In

DEM operation (assuming that the coil resistance

remains fixed), low inductor value has high efficiency

and high output voltage ripple. However, high inductor

value features low efficiency and less output voltage

ripple. The drawback of using high inductor value

includes larger physical size and lower load transient

response (especially at low input voltage level).

Ultrasonic Mode (USM)

The RT6310A/AH/B/BH/C/CH activates a unique type

of diode emulation mode with a minimum switching

frequency of 25kHz, called ultrasonic mode. The

acoustic frequency is avoided in ultrasonic mode.

Ultrasonic mode is selected by the EN/MODE voltage

level. If EN/MODE voltage ranges from 0.88V to 1.7V,

the device operates in ultrasonic mode.

When the internal 25kHz oscillator is triggered, the one-

shot on-time timer is activated for turning on high-side

MOSFET.

Once

the

one-shot

on-time

timer

completed, the low-side MOSFET is turned on with off-

time timer. After the one-shot on-time timer and off-time

timer are finished, the device keeps both high-side and

low-side MOSFET off and waits for next trigger.

In order to regulate output voltage with 25kHz minimum

switching frequency, the one-shot on-time timer and off-

time timer are adjusted based on load condition. In no-

load condition, the shorter one-shot on-time timer and

longer off-time timer are applied as initial value. In this

manner, the inductor current decreases to negative

value during the off-time state. When the output current

slowly increases from no load, the valley point of

inductor current is increased by reducing the width of

off-time timer until the inductor valley point reaches from

negative value to zero. In previous load condition, if the

output current is further increased, the width of on-time

timer is gradually increased from shorter value to

normal value before the switching frequency is higher

than 25kHz. Once the switching frequency is higher

than 25kHz with increasing output current, the behavior

of device is changed from ultrasonic mode to diode

emulation mode.

On-Time Reduction Function for DEM

In normal diode emulation mode, the output voltage

ripple of converter is proportional to on-time and

inversely proportional to load current. In order to have

smaller voltage ripple in light-load applications, the

RT6310 provides a smart reduction on-time function.

The

smart

reduction

on-time

function

naturally

decreases on-time when load current is decreasing.

Therefore, the output voltage ripple is reduced.

Spread Spectrum Function for DEM

In order to reduce the acoustic noise in diode emulation

mode, RT6310 provides spread spectrum function with

randomly adjusted on-time. The random variation value

7% of normal on-time value. Once the load condition

enters to CCM, the device disables the spread spectrum

function because switching frequency is much higher

than acoustic frequency.

RT6310A/AH 数据表(PDF) 11 Page - Richtek Technology Corporation

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