RT9164A-15 Ver la hoja de datos (PDF) - Richtek Technology

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RT9164A-15

1.0A Fixed and Adjustable Low Dropout Positive Voltage Regulators

Richtek Technology 

Preliminary

RT9164A

Application Information

Output voltage adjustment

Like most regulators, the RT9164A regulates the output

by comparing the output voltage to an internally generated

reference voltage. On the adjustable version as shown in

Figure 4, the VREF is available externally as 1.25V between

VOUT and ADJ. The voltage ratio formed by R1 and R2

should be set to conduct 10mA (minimum output load).

The output voltage is given by the following equation:

VOUT = VREF (1+

R2

R1

) + IADJ R2

On fixed versions of RT9164A, the voltage divider is

provided internally.

VIN

10uF

RT9164A

VIN

VOUT

ADJ

IADJ

65uA

VREF R1

CADJ

R2

VOUT

10uF

Figure 4. Basic Adjustable Regulator

Input Bypass Capacitor

An input capacitor is recommended. A 10µF tantalum on

the input is a suitable input bypassing for almost all

applications.

Adjust Terminal Bypass Capacitor

The adjust terminal can be bypassed to ground with a

bypass capacitor (CADJ) to improve ripple rejection. This

bypass capacitor prevents ripple from being amplified as

the output voltage is increased. At any ripple frequency,

the impedance of the CADJ should be less than R1 to

prevent the ripple from being amplified:

(2p * fRIPPLE * CADJ) < R1

The R1 is the resistor between the output and the adjust

pin. Its value is normally in the range of 100-200Ω. For

example, with R1 = 124Ω and fRIPPLE = 120Hz, the CADJ

should be > 11µF.

Output Capacitor

RT9164A requires a capacitor from VOUT to GND to

provide compensation feedback to the internal gain stage.

This is to ensure stability at the output terminal. Typically,

a 10µF tantalum or 50µF aluminum electrolytic is

sufficient.

Note: It is important that the ESR for this capacitor does

not exceed 0.5Ω.

The output capacitor does not have a theoretical upper

limit and increasing its value will increase stability. COUT =

100µF or more is typical for high current regulator design.

Load Regulation

When the adjustable regulator is used (Figure 5), the best

load regulation is accomplished when the top of the

resistor divider (R1) is connected directly to the output

pin of the RT9164A. When so connected, RP is not

multiplied by the divider ratio. For Fixed output version,

the top of R1 is internally connected to the output and

ground pins can be connected to low side of the load.

RT9164A

RP Parasitic

Line Resistance

VIN

VIN

VOUT

GND

R1

(Connect R1 to VOUT or case)

R2

RL

Connect R2 to load

Figure 5. Best Load Regulation Using Adjustable

Output Regulator

Thermal Protection

RT9164A has thermal protection which limits junction

temperature to 150°C. However, device functionality is

only guaranteed to a maximum junction tempe-rature of

+125°C. The power dissipation and junction temperature

for RT9164A in DPAK package are given by

DS9164A-01 December 2003

www.richtek.com

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