CS5205 datasheet(4/7 Pages) FCI

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The CS-5205 series of adjustable and fixed regulators are

designed to power the new generation of microprocessors.

The CS-5205 is designed to make use of multiple power

supplies, present in most systems, to reduce the dropout

voltage. One of the advantages of the two supply approach

is maximizing the efficiency.

The second supply is at least 1V greater than output voltage

and is providing the power for the control circuitry and

supplies the drive current to the NPN output transistor. This

allows the NPN output transistor to be driven into saturation.

For the control voltage the current requirement is small equal

to about 1% of the output current or approximately 50mA

for a 5A load. This drive current becomes part of the output

current. The maximum voltage on the Control pin is 15V.

The maximum voltage at the Power pin is 7V. By typing the

control and power inputs together the CS-5205 can also be

operated as a single supply device. In single supply operation

the dropout will be determined by the minimum control

voltage.

The new generation of microprocessors cycle load current

from several hundred milliamperes to several amperes in

tens of nanoseconds. Output voltage tolerances are tighter

and include transient response as part of the specification.

Designed to meet the fast current load step requirements of

these microprocessors, the CS-5205 also saves total cost by

needing less output capacitane to maintain regulation.

Both the fixed and adjustable versions have remote sense

pins, permitting very accurate regulation of output voltage.

As a result, over an output current range of 100mA to 5A,

the typical load regulation is less than 1mV.

For the fixed voltages the adjust pin is brought out allowing

the user to improve transient response by bypassing the

internal resistor divider.

Optimum transient response is

provided using a capacitor in the range of 0.1

F to 1

F for

bypassing the Adjust pin.

In addition to the enhancements mentioned, the reference

accuracy has been improved a factor of two with a

guaranteed initial tolerance of

1% at 25

and 1.6%

accuracy over the full temperature and load current range.

Typical applications for the CS-5205 include 3.3V to 2.5V

conversion with a 5V control supply, 5V to 4.2V

conversion with a 12V control supply or 5V to 3.6V

conversion with a 12V control supply. It is easy to obtain

dropout voltages of less than 0.5V at 2.5A along with

excellent static and dynamic specifications.

The device is

fully protected against overcurrent and overtemperature

conditions.

Application Information

The CS-5205 allows true Kelvin sensing for both the high

and low side of the load. As a result the voltage regulation

at the load can be easily optimized. Voltage drops due to

parasitic resistances between the regulator and the load

can be placed inside the regulation loop. The advantages

of remote sensing are illustrated in figures 1 through 3.

Figure 1 shows the device connected as a conventional 3

terminal regulator with the Sense lead connected directly

to the output of the device. Rp is the parasitic resistance of

the connections between the device and the load.

Trace A of figure 3 illustrates the effect of Rp.

Figure 2 shows the device connected to take advantage

of the remote sense feature. The Sense pin and the top

of the resistor divider are connected to the top of the

load; the bottom of the resistor divider is connected to

the bottom of the load. The effect on output regulation

can be seen in trace B of figure 3.

Grounding and Output Sensing

CS-5205 5A Low Dropout Positive Voltage Regulator

The circuit design used in the CS5205 series requires the

use of an output capacitor as part of the device frequency

compensation.

The addition of 150

F aluminum

electrolytic or a 22

F solid tantalum on the output will

ensure stability for all operating conditions.

Stability

CONTROL

5.0V

3.3V

CS5205

ADJ

POWER

SENSE

OUTPUT

LOAD

VOUT

FIGURE 1

VOUT

It is important to note that the voltage drops due to

Representative are not eliminated; they will add to the

dropout voltage of the regulator regardless. The CS-5205

can control thevoltage at the load as long as the

input-output voltage is greater than the total of the

dropout voltage of the deviceplus the voltage drop across

Rp .

CONTROL

5.0V

3.3V

CS5205

ADJ

POWER

SENSE

OUTPUT

Figure 1. Conventional Load Sensing

LOAD

Figure 2. Remote Load Sensing

Figure 3. Remote Sensing Improves Load Regulation

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