500mV to 5.5V Input, Ultrasonic

Boost Converter with Short-Circuit

Protection and True Shutdown

MAX18002

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Analog Devices | 12

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

*USM disabled for VOUT > 5V.

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

Soft-Start

When the EN logic goes high and VIN > VIN_UVLO, the MAX18002 starts up by turning on the bias circuitry after which

the resistance value at the RSEL pin is read to set the VOUT target voltage level. The MAX18002 addresses the issue of

high inrush current during start-up by having the high-side PMOS operate in linear mode (PMOS slew) until 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 and the output voltage ramps up with a slew rate of 3V/ms (typical) until the regulation

target.

If the MAX18002 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 MAX18002 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 product operation 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.

Automatic Pass-Through

Automatic pass-through mode is activated whenever VIN > VOUT. During the pass-through mode of operation, the

MAX18002 follows the VIN level and operates at a switching frequency of 29kHz (typical) in USM to stay away from

acoustic audible range.