DIO6905B

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© 2025 Dioo Microcircuits Co., Ltd. Jiangsu

DIO6905B • Rev. 1.2

- 9 -

Detailed Description

The DIO6905B uses constant on-time control with input voltage feed-forward to stabilize the switching frequency

over its full input voltage range. It achieves 2 A of output current from a 2.3 V to 5.5 V input voltage range with

excellent load and line regulation. The output voltage can be regulated as low as 0.6 V.

Constant-on-time control

When compared to fixed-frequency PWM control, constant-on-time control offers a simpler control loop and

faster transient response. By using input voltage feed-forward, the DIO6905B maintains a nearly constant

switching frequency across the input and output voltage ranges. The switching pulse on time can be estimated

with Equation (1):

μs

0.556

V

V

t

IN

OUT

ON





(1)

To prevent inductor current runaway during the load transient, the DIO6905B has a fixed minimum off time of

60 ns.

Enable (EN)

When the input voltage is greater than the under-voltage lockout (UVLO) threshold (typically 2.1 V), the

DIO6905B can be enabled by pulling EN higher than 1.2 V. Leaving EN floating or pulling it down to ground

disables the DIO6905B. There is an internal 1 MΩ resistor from EN to the ground.

When the DIO6905B is disabled, the part goes into output discharge mode automatically. The internal discharge

MOSFET provides a resistive discharge path for the output capacitor.

Soft-start

The DIO6905B uses a built-in soft-start (SS) that ramps up the output voltage at a controlled slew rate to avoid

overshooting at start-up. The soft-start time is about 0.6 ms, typically.

Current limit

The DIO6905B has a 2.4 A, minimum, high-side, switch-current limit. When the high-side switch reaches its

current limit, the DIO6905B remains in hiccup mode until the current drops. This prevents the inductor current

from continuing to rise and damaging components.

Short circuit and recovery

The DIO6905B enters short-circuit protection (SCP) mode when it reaches the current limit and attempts to

recover with hiccup mode. The DIO6905B disables the output power stage, discharges the soft-start capacitor,

and attempts to soft-start again automatically. If the short circuit condition remains after the soft start ends, the

DIO6905B repeats this cycle until the short circuit disappears and the output rises back to regulation levels.