Data Sheet

LT7826

analog.com

Rev. 0

11 of 19

BLOCK DIAGRAM

Figure 12. LT7826 Block Diagram

THEORY OF OPERATION

The LT7826 is a constant-frequency, open-loop switched capacitor/charge pump converter for high-power and high-

voltage applications. In steady-state operation, the internal switches are turned on and off to force the flying

capacitor between SWH and SWL, either parallel or serial, with the capacitor at VLOW. When the flying capacitor and

VLOW

capacitor are paralleled, the voltages on these capacitors are the same. When the flying capacitor and VLOW

capacitor are serial to VHIGH, the voltage on the flying capacitor plus the voltage on the VLOW capacitor equals the

voltage on VHIGH. With this switched cap operation, the VLOW pin voltage remains close to half of the VHIGH voltage

in the steady state, and it is not sensitive to variable loads due to very low output impedance at a high switching

frequency. The LT7826 does not regulate the output voltage with a closed-loop feedback system. However, it stops

switching when fault conditions occur, such as a VLOW pin shorted to GND, an overcurrent event, and

overtemperature protection.

Start-Up and Shutdown (RUN)

The LT7826 is in shutdown mode when the RUN pin is pulled down. In shutdown mode, most internal circuits are

turned off, including the INTVCC regulator, and the entire LT7826 consumes less than 4µA current. Releasing the RUN

pin allows an internal 0.55µA current to pull up this pin and enable the INTVCC regulator when the RUN pin voltage

exceeds 1.2V. Alternately, the RUN pin can be externally pulled up or driven directly by a logic. Do not exceed the

absolute maximum rating of 6V on this pin.

INTVCC Power and UVLO

INTVCC is generated by an internal low dropout (LDO) and regulated to 4V for internal and gate-drive circuitry. It is

powered from VLOW when VVLOW is higher than 3.8V; otherwise, it is powered from VHIGH. When VINTVCC rises above its

UVLO threshold of 3.45V, LT7826 is ready for switching operation. When VINTVCC decreases below 3.15V, LT7826 stops

switching. A ceramic or other low-ESR capacitor with a capacitance of 1µF or up should be connected between

INTVCC and the ground, and placed close to these pins.

G1

G2

G3

G4

GFLT

1.6MΩ

550nA

RUN

MODE

FAULT

SGND

SWH

INTVCC

PGND

LT7826

VHIGH

BSTH

SWL

BSTL

FLV

VLOW

CONTROL

LOGIC