RT8223A 查看數據表（PDF） - Richtek Technology

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RT8223A

High Efficiency, Main Power Supply Controller for Notebook Computers

Richtek Technology 

RT8223A/B

Discharge Mode (Soft Discharge)

When ENTRIPx is low and a transition to standby,

shutdown mode occurs, or the output under voltage fault

latch is set, the outputs discharge mode will be triggered.

During discharge mode, there is one path to discharge

the outputs capacitor residual charge. That is output

capacitor discharge to GND through an internal MOS

switch.

Shutdown Mode

The RT8223A/B SMPS1, SMPS2, VREG3 and VREG5

have independent enabling control. Drive EN, ENTRIP1,

ENTRIP2 and ENC below the precise input falling edge

trip level to place the RT8223A/B in its low power shutdown

state. The RT8223A/B consumes only 20μA of input

current while in shutdown.

Power-Up Sequencing and On/Off Controls

(ENTRIPx, ENC)

ENTRIP1 and ENTRIP2 control SMPS power-up

sequencing. When the RT8223A/B applies in the single

channel mode, ENTRIP1 or ENTRIP2 enables the

respective outputs when ENTRIPx voltage rises above

0.4V. Furthermore, the RT8223A/B applies in the dual

channel mode. ENC enables the outputs when ENC

voltage rises above 2V.

If both of ENTRIP1 and ENTRIP2 become higher than the

enable threshold voltage at a different time (without 60μs),

one can force the latter one output starts after the former

one regulates.

Output Voltage Setting (FBx)

Connect FBx directly to GND or VREG5 to enable the

fixed, SMPS output voltages (3.3V and 5V). Connect a

resistor voltage divider at the FBx between the VOUTx

and GND to adjust the respective output voltage between

2V and 5.5V (Figure 4). Choose R2 to be approximately

10kΩ, and solve for R1 using the equation :

VOUTx = VFBx

×

⎡⎢⎣1+

⎛⎜⎝

R1

R2

⎞⎟⎠⎤⎥⎦

where VFBx is 2V (typ.).

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VREG5 connects to VOUT1 through an internal switch

only when VOUT1 is above the VREG5 automatic switch

threshold (4.66V). VREG3 connects to VOUT2 through

an internal switch only when VOUT2 is above the VREG3

automatic switch threshold (3V). This is the most effective

way when the fixed output voltages are used. Once VREGx

is supplied from VOUTx, the internal linear regulator turns

off. This reduces internal power dissipation and improves

efficiency when the VREGx is powered with a high input

voltage.

VIN

UGATEx

PHASEx

LGATEx

VOUTx

FBx

PGND

GND

VOUTx

R1

R2

Figure 4. Setting VOUTx with a Resistor-Divider

Output Inductor Selection

The switching frequency (on-time) and operating point (%

ripple or LIR) determine the inductor value as shown as

follows :

L=

TON × (VIN − VOUTx )

LIR × ILOAD(MAX)

where LIR is the ratio of the peak to peak ripple current to

the average inductor current.

Find a low loss inductor having the lowest possible DC

resistance that fits in the allotted dimensions. Ferrite cores

are often the best choice, although powdered iron is

inexpensive and can work well at 200kHz. The core must

be large enough not to saturate at the peak inductor current

(IPEAK) :

IPEAK = ILOAD(MAX) + [(LIR / 2) x ILOAD(MAX)]

This inductor ripple current also impacts transient-response

performance, especially at low VIN − VOUTx differences.

Low inductor values allow the inductor current to slew

faster, replenishing charge removed from the output filter

capacitors by a sudden load step. The peak amplitude of

the output transient VSAG is also a function of the output

transient. The VSAG also features a function of the

DS8223A/B-04 April 2011

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