TC1303B-AO2EUNTR datasheet(18/30 Pages) MICROCHIP

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TC1303B

DS21949A-page 18

5.0

APPLICATION

CIRCUITS/ISSUES

5.1

Typical Applications

The TC1303B 500 mA buck regulator + 300 mA LDO

with power-good operates over a wide input voltage

range (2.7V to 5.5V) and is ideal for single-cell Li-Ion

battery-powered applications, USB-powered applica-

tions, three-cell NiMH or NiCd applications and 3V to

5V regulated input applications. The 10-pin MSOP and

3X3 DFN packages provide a small footprint with

minimal external components.

5.2

Fixed Output Application

A typical VOUT1 fixed output voltage application is

shown in “Typical Application Circuits” on page 3. A

4.7 µF VIN1 ceramic input capacitor, 4.7 µF VOUT1

ceramic capacitor, 1.0 µF ceramic VOUT2 capacitor and

4.7 µH inductor make up the entire external component

solution for this dual-output application. No external

dividers or compensation components are necessary.

For this application, the input voltage range is 2.7V to

4.2V, VOUT1 = 1.5V at 500 mA, while VOUT2 =2.5V at

300 mA.

5.3

Adjustable Output Application

A typical VOUT1 adjustable output application is also

shown in “Typical Application Circuits” on page 3.

For this application, the buck regulator output voltage is

adjustable by using two external resistors as a voltage

divider. For adjustable output voltages, it is recom-

mended that the top resistor divider value be 200 k

Ω.

The bottom resistor divider can be calculated using the

following formula:

EQUATION 5-1:

Example:

RTOP =200 kΩ

VOUT1 =2.1V

VFB

=0.8V

RBOT =200 kΩ x (0.8V/(2.1V – 0.8V))

RBOT =123 kΩ (Standard Value = 121 kΩ)

For adjustable output applications, an additional R-C

compensation is necessary for the buck regulator

control loop stability. Recommended values are:

RCOMP =4.99kΩ

CCOMP =33 pF

An additional VIN2 capacitor can be added to reduce

high frequency noise on the LDO input voltage pin

(VIN2). This additional capacitor (1 µF on page 3) is not

necessary for typical applications.

5.4

Input and Output Capacitor

Selection

As with all buck-derived dc-dc switching regulators, the

input current is pulled from the source in pulses. This

places a burden on the TC1303B input filter capacitor.

In most applications, a minimum of 4.7 µF is recom-

mended on VIN1 (buck regulator input voltage pin). In

applications that have high source impedance or have

long leads (10 inches) connecting to the input source,

additional capacitance should be used. The capacitor

type can be electrolytic (aluminum, tantalum, POSCAP,

OSCON) or ceramic. For most portable electronic

applications, ceramic capacitors are preferred due to

their small size and low cost.

For applications that require very low noise on the LDO

output, an additional capacitor (typically 1 µF) can be

added to the VIN2 pin (LDO input voltage pin).

Low ESR electrolytic or ceramic can be used for the

buck regulator output capacitor. Again, ceramic is

recommended because of its physical attributes and

cost. For most applications, a 4.7 µF is recommended.

Refer to Table 5-1 for recommended values. Larger

capacitors (up to 22 µF) can be used. There are some

advantages in load step performance when using

larger value capacitors. Ceramic materials X7R and

X5R have low temperature coefficients and are well

within the acceptable ESR range required.

TABLE 5-1:

TC1303B RECOMMENDED

CAPACITOR VALUES

BOT

TOP

OUT1

–

--------------------------------

⎝⎠

⎛⎞

C(VIN1)C(VIN2)COUT1

COUT2

min

4.7 µF

none

4.7 µF

1 µF

max

none

22 µF

10 µF

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