MAX5938LEEE+【PDF 15/26 页】IC HOT-SWAP CTRLR -48V 16-QSOP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录43

11页 12页 13页 14页 [15页]16页 17页 18页 19页

Determine the trip voltages these values will actually

yield for rising and falling voltages. Rising voltages use

the V

REF

= 1.25V reference threshold, while falling volt-

ages use V

= 1.125V reference threshold.

1) R

TOT

= R

+ R

2) V

OV,RISING

= V

REF

x R

TOT

/ R

3) V

OV,FALLING

= V

x R

TOT

/ R

4) V

ON,RISING

= V

REF

x R

TOT

/ (R

+ R

)

5) V

ON,FALLING

= V

x R

TOT

/ (R

+ R

)

6) V

OFF

= V

REF

x R

TOT

/ (R

+ R

)

The resulting voltage levels are V

OV,RISING

= 79.82V

?.5%, V

OV,FALLING

= 71.84V ?%, V

ON,RISING

42.32V ?.5%, V

ON,FALLING

= 38.09V ?%, and V

OFF

= 38.26V ?.5%. The voltage tolerance does not

account for the tolerance of the resistors.

Setting the Circuit-Breaker and

Short-Circuit Thresholds

The MAX5938 can operate with a wide range of power

MOSFETs to meet the requirements of almost any appli-

cation. MOSFETs mentioned here are done to demon-

strate certain capabilities and features of the MAX5938.

They should not be construed as a recommendation or a

limitation of the interoperability of the MAX5938.

In the implementation of the circuit-breaker and short-

circuit functions, the MAX5938 eliminates the need for

an external current-sense resistor at the source of the

power MOSFET. As in any other hot-swap controller,

the proper circuit-breaker threshold for an application

must take into account the DC level of V

OUT

, while at

the same time accommodating the AC response of

OUT

to the modulation of V

. The AC response from

to V

OUT

is dependent on the parasitics of the load,

especially the load capacitor, in conjunction with the

DS(ON)

of the power MOSFET. It behaves as a highly

dampened second-order system. As such, this system

functions as a bandpass filter from V

to V

OUT

. The

response of V

OUT

to load-switching currents and volt-

age ripple and noise from the backplane power supply

must be taken into account. Adequate margin must be

provided between V

, V

, and the DC level of V

OUT

which depends on the R

DS(ON)

of the power MOSFET

(with V

at 10V) and the maximum current the load is

expected to draw. While the circuit-breaker threshold

has glitch rejection for V

OUT

excursions lasting less

than 1.4ms, the short-circuit detection is designed to

respond very quickly (less than 330ns) to a short cir-

cuit. In the application, select a value for R

CB_ADJ

resulting in a V

that exceeds the product of R

DS(ON)

and the maximum load current plus one half the peak-

to-peak AC response of V

OUT

to load-switching cur-

rents and the noise and ripple at V

DS(ON)

(&) x I

LOAD,MAX

(mA) +

x VOUT

< V

(mV)

where

(mV) =

x I

CB_ADJ

(礎) x [R

INT

(k&)

+ R

CB_ADJ

(k&)]

DS(ON)

in a power MOSFET has a positive tempera-

ture coefficient and the MAX5938, when placed adja-

cent to the power MOSFET, tracks and compensates

for this temperature coefficient. In the MAX5938, V

half of V

, which is set by placing an external resis-

tance between CB_ADJ and V

. The minimum

(default) short-circuit threshold voltage, V

, is set by

an internal 2k& precision-trimmed (?.5%) resistor pro-

viding a minimum series resistance and a temperature-

compensated 50礎 (+25癈) current source. When

CB_ADJ is connected to V

this gives a 50mV circuit-

breaker threshold. When an external resistor, R

CB_ADJ

is placed between CB_ADJ and V

, the new circuit-

breaker threshold becomes:

(mV) =

x V

(mV) =

x I

CB_ADJ

(礎)

x (2k& + R

CB_ADJ

)

and at +25癈, it becomes:

(mV) =

x 50礎

x (2k& + R

CB_ADJ

)

The short-circuit and circuit-breaker voltages are sensed

at V

OUT

, which is the drain of the power MOSFET. The

DS(ON)

of the MOSFET is the current-sense resistance

and so the total current through the load and load

capacitance is the drain current of the power MOSFET.

Accordingly, the voltage at V

OUT

as a function of

MOSFET drain current is:

OUT

= I

D,MOSFET

x R

DS(ON)

The temperature compensation of the MAX5938 is

designed to track the R

DS(ON)

of the typical power

MOSFET. Figure 14 shows the typical normalized temp-

co of the circuit-breaker threshold along with the nor-

malized tempco of R

DS(ON)

for several typical power

MOSFETS. When determining the circuit-breaker

threshold in an application go to the power MOSFET

manufacturers data sheet and locate the maximum

DS(ON)

at +25癈 with a V

of 10V. Next, find the fig-

ure presenting the tempco of normalized R

DS(ON)

on-resistance vs. temperature. Since this curve is in

-48V Hot-Swap Controller with V

Step Immunity,

No R

SENSE

, and Overvoltage Protection

______________________________________________________________________________________ 15

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式