REG711

7

SBVS027A

THEORY OF OPERATION

The REG711 regulated charge pump provides a regulated

output voltage for input voltages ranging from less than the

output to greater than the output. This is accomplished by

automatic mode switching within the device. When the input

voltage is greater than the required output, the unit functions

as a variable pulse-width switch-mode regulator. This opera-

regulated output voltage.

A conversion clock of 50% duty cycle is generated. During

the first half cycle the FET switches are configured as shown

half cycle the FET switches are configured as shown in

output voltage is regulated by skipping clock cycles as

necessary.

PEAK CURRENT REDUCTION

In normal operation, the charging of the pump and output

capacitors usually leads to relatively high peak input cur-

rents which can be much higher than that of the average load

current. The regulator incorporates circuitry to limit the

input peak current, lowering the total EMI production of the

device and lowering output voltage ripple and input current

required by input current peaks.

PROTECTION

The regulator has thermal shutdown circuitry that protects it

from damage caused by overload conditions. The thermal

protection circuitry disables the output when the junction

temperature reaches approximately 160

°C, allowing the de-

vice to cool. When the junction temperature cools to ap-

proximately 140

°C, the output circuitry is automatically re-

enabled. Continuously running the regulator into thermal

shutdown can degrade reliability. The regulator also pro-

vides current limit to protect itself and the load.

SHUTDOWN MODE

A control pin on the regulator can be used to place the device

into an energy-saving shutdown mode. In this mode, the

cent current is reduced to 2

µA maximum.

FIGURE 1. Simplified Schematic of the REG711 Operating

in the Step-Down Mode.

When the input voltage is less than the required output

voltage, the device switched to a step-up or boost mode of

operation, as shown in Figure 2.

FIGURE 2. Simplified Schematic of the REG711 Operating in the Step-Up or Boost Mode.

C

PUMP

C

IN

C

OUT

V

OUT

V

IN

Q

1

Q

3

Q

2

Q

4

OFF

OFF

SWITCHED

ON

Step-Down (Buck) Mode

C

PUMP

C

IN

C

OUT

V

OUT

V

IN

Q

1

Q

3

Q

2

Q

4

OFF

ON

ON

OFF

Step-Up (Boost) Mode

+

–

(A)

C

PUMP

C

IN

C

OUT

V

OUT

V

IN

Q

1

Q

3

Q

2

Q

4

ON

OFF

OFF

ON

+

–

(B)