30V 1.2A 1.4MHz Synchronous Step-Down Regulator

Functional Block Diagram

VCC REGULATOR

OSCILLATOR

REFERENCE

1M

400k

56pF

1pF

COMPARATOR

ON TIME CONTROL

LOGIC CONTROL

∑

BOOST

REGULATOR

HS

DRIVER

LS

DRIVER

VCC

VCC

VIN

EN

FB

GND

SW

BS

CURRENT LIMIT

COMPARATOR

+

+

-

CURRENT SENSE

AMPLIFIER

RSEN

ERROR AMPLIFIER

+

-

+

-

Figure 2.

Block Diagram

Functions Description

Internal Regulator

The

is a current mode step down DC/DC converter that provides excellent transient response with no

extra external compensation components. This device contains an internal, low resistance, high voltage power

MOSFET, and operates at a high 1.4MHz operating frequency to ensure a compact, high efficiency design with

excellent AC and DC performance.

Error Amplifier

The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current

proportional to the difference between the two. This output current is then used to charge or discharge the internal

compensation network to form the COMP voltage, which is used to control the power MOSFET current. The

optimized internal compensation network minimizes the external component counts and simplifies the control loop

design.

Internal Soft-Start

The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the

chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.8V. When it is lower

than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is

higher than REF, REF regains control. The SS time is internally fixed to 1.6ms.

Over Current Protection & Hiccup

The HM8112 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current

limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold,

typically 25% below the reference. Once a UV is triggered, the HM8112 enters hiccup mode to periodically restart

HM8112

HM8112