500mV to 5.5V Input nanoPower

Boost Converter with Short-Circuit

Protection

and True Shutdown

MAX18000

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Analog Devices | 12

4.6

20

4.7

16.9

4.8

14

4.9

11.8

5.0

10.0

5.1*

8.45

5.2*

7.15

5.3*

5.9

5.4*

4.99

5.5*

Short to Ground

*nanoPower mode disabled for VOUT > 5V.

**Use a standard 1% resistor at RSEL pin.

Soft-Start

When the EN logic goes high and VIN > VIN_UVLO, the MAX18000 starts up by turning on the bias circuitry, after which

the resistance value at the RSEL pin is read to set theP VOUT target voltage level. The IC addresses the issue of high

inrush current during startup by having the high-side PMOS operate in linear mode (PMOS slew) till VOUT = VIN. The

PMOS slew phase typically takes about 350µs.

After the PMOS slew is complete, the high-side PMOS turns off, and the IC enters a boost-slew mode. In the boost slew

mode of operation, the part switches such that the output voltage ramps up at a slew rate of 3V/ms (typical) until the

regulation target.

If the IC sees an output voltage level of less than 0.5V after the PMOS slew timer expires (350µs typical), it enters short-

circuit protection mode. In short-circuit protection mode, the IC stops switching, and the PMOS current is limited to 700mA

(typical).

EN

TDLY_EN

TSS_LINEAR = 350µs

VOUT

SLEWSS_BOOST = 3V/ms

VIN

BOOST MODE

Figure 2. Soft-Start Behavior

Boost Control Scheme

The MAX18000 operates based on an adaptive on-time current-mode control. Adaptive on-time is used to get a fast

transient response and better efficiency across the operating range. In both continuous conduction mode (CCM) and

discontinuous conduction mode (DCM), the on-time is adjusted depending on the input voltage and target output voltage.

nanoPower Mode

The MAX18000 automatically enters nanoPower mode when the load current is very low to achieve high efficiency at light

loads. When the load current is reduced, the switching frequency also reduces. When the switching frequency reduces