4

The CS5201 is designed to make use of multiple power

supplies, 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.

This drive current becomes part of the output

current. The maximum voltage on the Control pin is 12V.

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

control and power inputs together the CS5201 can also

be operated as a single supply device. In single supply

operation the dropout will be determined by the minimum

control voltage.

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 1A, 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 CS5201 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. The device is fully

protected against overcurrent and overtemperature

conditions.

The CS5201 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 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.

It is important to note that the voltage drops due to Rp,

are not eliminated; they will add to the dropout voltage of

the regulator regardless.

The CS5201 can control the

voltage at the load as long as the input-output voltage is

greater than the total of the dropout voltage of the device

plus the voltage drop across Rp .

The circuit design used in the CS5201 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.

Application Information

Grounding and Output Sensing

Stability

CONTROL

CONTROL

5.0V

5.0V

3.3V

3.3V

R2

R2

(

I

)(

OUT

P

R1

R1

Rp

Rp

R

R

CS5201

CS5201

ADJ

ADJ

POWER

POWER

SENSE

SENSE

OUTPUT

OUTPUT

Figure 1. Conventional Load Sensing

Figure 2. Remote Load Sensing

Figure 3. Remote Sensing Improves Load Regulation

LOAD

LOAD

TIME

A

B

FIGURE 1

FIGURE 2

CS-5201 1Amp Low Dropout Positive Voltage Regulator