Functions Description

Internal Regulator

The

HM1586 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 600K 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 0.923V. 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

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 Y3831 enters hiccup mode to periodically restart the part. This

protection mode is especially useful when the output is dead-short to ground. The average short circuit current is

greatly reduced to alleviate the thermal issue and to protect the regulator. The

HM1586 exits the hiccup mode once

the over current condition is removed.

Startup and Shutdown

If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first,

generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides

stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal

shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP

voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown

command.

Applications Information

Setting the Output Voltage

HM1586 require an input capacitor, an output capacitor and an inductor. These components are critical to the

performance of the device.

HM1586 are internally compensated and do not require external components to achieve