SMH4811A(2000) 데이터 시트보기 (PDF) - Summit Microelectronics

부품명

상세내역

일치하는 목록

SMH4811A
(Rev.:2000)

Distributed Power Hot-Swap Controller

Summit Microelectronics 

The dropper resistor value is calculated from:

RD = VSMIN – VDDMAX

IDD + ILOAD

Where VSMIN is the lowest operating supply voltage,

VDDMAX is the upper limit of the SMH4811A supply voltage,

IDD is minimum current required for the SMH4811A to

operate, and ILOAD is any additional load current from the

2.5V and 5V outputs and between VDD and VSS.

The min/max current limits are easily met using the drop-

per resistor except in circumstances where the input

voltage may swing over a very wide range, e.g., input

varies between 20V and 100V. In these circumstances it

may be necessary to add an 11V zener diode between

VDD and VSS to handle the wide current range. The zener

voltage should be below the nominal regulation voltage of

the SMH4811A so that it becomes the primary regulator.

MOSFET VDS(ON) Threshold

The drain sense input on the SMH4811A monitors the

voltage at the drain of the external power MOSFET switch

with respect to VSS. When the MOSFET’s VDS is below the

user-defined value the switch is considered to be ON. The

VDS(ON) is adjusted using the resistor RT in series with the

drain sense protection diode. This protection or blocking

diode prevents high voltage breakdown of the drain sense

input when the MOSFET switch is OFF. An inexpensive

1N4148 diode offers protection up to 75V. The VDS(ON)

threshold is calculated from:

VDS = VSENSE – (ISENSE × RT) –

VDIODE – (IRS × RS)

Where VDIODE is the forward voltage drop of the protection

diode, and IRS is the current flowing through the circuit

breaker sense resistor RS. The VDS(ON) threshold varies

over temperature due to the temperature dependence of

VDIODE. Using 100kΩ for RT gives an approximate

VDS(ON) threshold of:

VDS = 2.5V – (10µA × 100kΩ) – 0.5V = 1V

SMH4811A

SUMMIT MICROELECTRONICS, Inc.

2044 4.1 8/1/00

9

Share Link: