REG710

SBAS221E − DECEMBER 2001 − REVISED SEPTEMBER 2003

www.ti.com

7

THEORY OF OPERATION

The REG710 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 au-

tomatic mode switching within the device. When the input

voltage is greater than the required output, the unit functions

as a variable frequency switch-mode regulator. This opera-

lated output voltage.

OFF

SWITCHED

Step−Down (Buck) Mode

OFF

ON

C

PUMP

Q

1

Q

3

Q

2

Q

4

C

IN

C

OUT

V

OUT

V

IN

Figure 1. Simplified Schematic of the REG710

Operating in the Step-Down Mode

When the input voltage is less than the required output

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

operation, as shown in Figure 2.

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

the first half cycle the FET switches are configured as

During the second half cycle the FET switched are config-

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 cur-

charge required by input current peaks.

PROTECTION

The regulator has thermal shutdown circuitry that protects

it from damage caused by overload conditions. The ther-

mal protection circuitry disables the output when the junc-

tion temperature reached approximately 160

°C, allowing

the device to cool. When the junction temperature cools to

approximately 140

°C, the output circuitry is automatically

reenabled. 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 de-

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

cent current is reduced to 1

µA maximum.

Step−Up (Boost) Mode

(A)

(B)

OFF

ON

ON

OFF

OFF

ON

ON

OFF

Figure 2. Simplified Schematic of the REG710 Operating in the Step-Up or Boost Mode