500mV to 5.5V Input nanoPower

Boost Converter with Short-Circuit

Protection

and True Shutdown

MAX18000

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Analog Devices | 13

below 28kHz (typical), the part enters nanoPower mode. In nanoPower mode, the part turns off the error amplifier and

other internal blocks to reduce the power consumption and goes to sleep. Once the VOUT level drops below the threshold,

the part wakes up and initiates switching cycles to bring the output voltage into regulation. The device regulates to 102.5%

of the target voltage when operating in nanoPower mode. When the load is increased and the VOUT level drops below

the threshold, the part starts switching and enters normal operation (DCM or CCM mode).

VOUT

ILOAD

FMIN

FMIN

FMIN

VOUT_TARGET

1.025 x VOUT_TARGET

(TYP.)

LOW-POWER MODE

FMIN

FMIN

Figure 3. nanoPower Mode of Operation

Thermal Shutdown

When the junction temperature exceeds TSHUT_R (+165°C typical), the converter is turned off until the temperature drops

to TSHUT_F (+150°C typical), after which the part starts up again. If the fault condition persists, power is cycled on and

off until the fault is cleared.

Overcurrent Protection

The IC features a cycle-to-cycle peak current limit of 3.6A (typical) to protect the IC and the system from overload

conditions. When the IC is in boost mode and the inductor current hits the current limit, the PMOS is turned on to start a

discharge cycle and bring the inductor current down.

Short-Circuit Protection

When the MAX18000 is hard shorted and the output voltage falls below 0.5V, it enters the hard short state. In the hard-

short condition, the part stops switching, and the PMOS switch limits the short-circuit current from the input to 0.7A

(typical).

If the fault persists, the heat generated in the PMOS switch due to the short-circuit current may cause the part to enter

thermal shutdown.

When the fault is removed, the part enters the PMOS slew until VIN = VOUT. After the PMOS slew is complete, the IC

skips the boost slew phase (that is observed during startup) and enters the boost mode of operation. This operation could

lead to an overshoot in output voltage of about 10% (typical) when VIN and VOUT are close to each other.

SHORT

VOUT

ILX

IPEAK_LX = 3.6A

ISC = 0.7A

Figure 4. Short-Circuit Operation