REG710 Datasheet, PDF (7/15 Pages) Texas Instruments – 60MA SWITCHED CAP BUCK/BOOST CONVERTER

REG710
www.ti.com
SBAS221E − DECEMBER 2001 − REVISED SEPTEMBER 2003
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-
tion is shown in Figure 1. Transistors Q₁ and Q₃ are held off,
Q₄ is on, and Q₂ is switched as needed to maintain a regu-
lated output voltage.
V_IN
Q₁
OFF
Q₂
SWITCHED
C_PUMP
During the second half cycle the FET switched are config-
ured as shown in Figure 2B, and the voltage on C_PUMP is
added to V_IN. The 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 cur-
rent ripple. Input capacitor (C_IN) supplies most of the
charge required by input current peaks.
Q₃
C_IN OFF
Q₄
ON
V_OUT
C_OUT
Step−Down (Buck) Mode
Figure 1. Simplified Schematic of the REG710
Operating in the Step-Down Mode
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.
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
shown in Figure 2A, and C_PUMP charges to V_IN.
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,
the output is disconnected from the input as long as V_IN is
greater than or equal to minimum V_IN and the input quies-
cent current is reduced to 1µA maximum.
V _IN
Q₁
OFF
Q₃
C_IN O N
C _PUMP
Q₂
ON
Q₄
OFF
V _OUT
C _OUT
V _IN
Q₁
ON
Q₃
C_IN OFF
C _PUMP
Q₂
OFF
Q₄
ON
V _OUT
C _OUT
(A)
Step−Up (Boost) Mode
(B)
Figure 2. Simplified Schematic of the REG710 Operating in the Step-Up or Boost Mode
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