MP28200 – 5.5V, 200

MP28200 Rev.1.0

www.MonolithicPower.com

13

10/10/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2016 MPS. All Rights Reserved.

The PG comparator is active when the device is

enabled. It is driven to a high impedance once

the output voltage trips the PG threshold (90%

of the regulation voltage, typically) and is pulled

low once the output voltage falls below the PG

hysteresis threshold (80% of the regulation

voltage, typically). The output is also pulled low

when the input voltage is lost or the part is

disabled.

Output Discharge Function

The step-down regulator features the output

discharge function once it is disabled. This

feature prevents residual charge voltages on

capacitors, which may impact a proper power-

up of the system. When the input voltage is

high and the related converters are disabled,

the output discharge is active.

100% Duty Cycle Mode

When the input voltage reduces and is lower

than the regulation output voltage, the output

voltage drops, and the on time increases.

Further reducing the input voltage drives the

MP28200 into 100% duty cycle mode. The

high-side switch is always on, and the output

voltage is determined by the loading current

switch and inductor.

Current Limit

The MP28200 has an internal current limit for

the step-down converter.

The high-side switch current is monitored cycle-

by-cycle and compares with the current-limit

threshold. Once the current-limit comparator is

triggered, the high-side switch is turned off and

the low-side switch is turned on, reducing the

inductor current. Until the low-side switch

current is lower than the low-side current limit,

the high-side switch is not allowed to turn on

again.

Short Circuit and Recovery

If the output voltage of the buck converter is

shorted to GND, the current limit is triggered. If

the current limit is triggered every cycle for

200µs continuously, the MP28200 enters

hiccup mode for the buck converter. The short-

circuit condition can also be triggered when the

output voltage is lower than 50% of the

regulation output voltage and when the current

limit is reached simultaneously. The buck

disables the output power stage, discharges the

output voltage, and then attempts to recover

after a hiccup. If the short-circuit condition

remains, the MP28200 repeats this operation

until the short-circuit is removed and the output

rises back to regulation levels.

Thermal Shutdown Circuit and Recovery

When the thermal shutdown signal is triggered,

the MP28200 turns off and restarts when the

temperature falls below the thermal hysteresis.