REG710_1 Datasheet, PDF (8/22 Pages) Texas Instruments – 60mA, 5.0V, Buck/Boost Charge Pump in ThinSOT-23 and ThinQFN

REG710
SBAS221F – DECEMBER 2001 – REVISED MARCH 2008............................................................................................................................................... www.ti.com
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 automatic 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
operation is shown in Figure 18. Transistors Q₁ and
Q₃ are held off, Q₄ is on, and Q₂ is switched as
needed to maintain a regulated output voltage.
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 19.
A conversion clock of 50% duty cycle is generated.
During the first half cycle the FET switches are
configured as shown in Figure 19A, and C_PUMP
charges to V_IN.
During the second half cycle the FET switched are
configured as shown in Figure 19B, 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 currents 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 ripple. Input
capacitor (C_IN) supplies most of the charge required
by input current peaks.
V_IN
Q₁
OFF
Q₃
C_IN OFF
C_PUMP
Q₂
SWITCHED
Q₄
ON
V_OUT
C_OUT
Step-Down (Buck) Mode
Figure 18. Simplified Schematic of the REG710 Operating in the Step-Down Mode
V_IN
Q₁
OFF
Q₃
C_IN ON
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 19. Simplified Schematic of the REG710 Operating in the Step-Up or Boost Mode
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