RT9201 Ver la hoja de datos (PDF) - Richtek Technology

Número de pieza

componentes Descripción

Fabricante

RT9201

High Efficiency PWM Step-Down DC-DC Converter

Richtek Technology 

RT9201

4

VLX 2

(V)

0

Sub-Harmonic at Boundary

Condition

100

VOUT

(mV) 0

-100

VIN = 3.8V, VOUT = 3.3V

IOUT = 600mA, COUT = 100uF

Time (10µs/Div)

Figure 1

BounMdina.ryInopfutPVWoMltaganedvsL.oOwu-tDpruotpCouurtreMnot de

5.50

5.00

PWM Mode

4.50

4.00

VOUT = 3.3V

3.50

3.00

2.50

VOUT = 2.5V

VOUT = 1.8V

2.00

Low Dropout Mode

1.50

1.00

0

100 200 300 400 500 600 700

OutpuItOCUTur(rmenAt)(mA)

Figure 2

Over Current Protection

The RT9201 continuously monitors the inductor current

by sensing the voltage across the PMOSFET when it

turns on. When the inductor current is higher than current

limit threshold (1A typical), OCP activates and forces the

PMOSFET turning off to limit inductor current cycle by

cycle.

The current limit is set to 50% level of normal condition

when the output voltage is lower than its 50% normal

level. This can minimize the power loss and protect the

device when over current or output short circuit occurs.

Once output voltage drops below to its 50% normal level

DS9201-12 August 2007

due to over current or short circuit, it can build up only

when output current is lower 50% of normal current limit

threshold.

Output Voltage Setting and Feedback Network

The output voltage can be set from VREF to VIN by a voltage

divider as:

VOUT

=

VREF

×

RF1 + RF2

RF2

The internal VREF is 0.8V with 1% accuracy. In practical

application, keep RF2 = 390kΩ and CF2 = 10pF

respectively and choose appropriate RF1 and CF1

according to the required output voltage. Make sure that

the product of RF1 and CF1 is about 8200kΩ-pF. The

following table shows recommended feedback network

as well as inductor for some typical output voltages.

Table 1. Component Selection for Typical Application

VOUT RF1

(V) (Ω)

CF1 RF2 CF2 LX CSS

(pF) (Ω) (pF) (µH) (pF)

0.85 24k 330 390k 10 4.7 330

1.5 343k 22 390k 10 6.8 470

2.5 820k 10 390k 10 10 680

3.3 1.2M 5.6 390k 10 10 1000

Inductor Selection

The output inductor is suggested as the above table for

optimal performance. Make sure that the inductor will

not saturate over the operation conditions including

temperature range, input voltage range, and maximum

output current. If possible, choose an inductor with rated

current higher than 1A so that it will not saturate even

under circuit condition.

Input Capacitor Selection

The input capacitor can filter the input peak current and

noise at input voltage source. The capacitor with low ESR

(effective series resistance) provides the small drop

voltage to stabilize the input voltage during the transient

loading. For input capacitor selection, the ceramic

capacitors larger than 10µF is recommend. The capacitor

must conform to the RMS current requirement. The

maximum RMS ripple current is calculated as :

IRMS = IOUT(MAX)

VOUT (VIN − VOUT )

VIN

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