ADM1177-2ARMZ-R7 datasheet(8/16 Pages) AD

Nome de Peças	ADM1177-2ARMZ-R7

Descrição Electrónicos	Hot Swap Controller and Digital Power Monitor with Soft-Start Pin

Download	16 Pages

Scroll/Zoom	100%

Fabricante Electrônico	AD [Analog Devices]

Página de início	http://www.analog.com

Logo

8 / 16 page

ADM1177

Preliminary Technical Data

Rev. PrD | Page 8 of 16

TIMER FUNCTION

The TIMER pin handles several timing functions with an

external capacitor, CTIMER. There are two comparator thresholds:

VTIMERH (0.2 V) and VTIMERL (1.3 V). The four timing current

sources are a 5 µA and a 60 µA pull-up, and a 2 µA and a

100 µA pull-down. The 100 µA is a non-ideal current source

approximating a 7 kΩ resistor below 0.4 V.

These current and voltage levels, together with the value of

CTIMER that the user chooses, determine the initial timing cycle

time, the fault current limit time, and the hotswap retry duty

cycle.

GATE AND TIMER FUNCTIONS DURING A

HOTSWAP

During hot insertion of a board onto a live supply rail at VCC,

the abrupt application of supply voltage charges the external

FET drain/gate capacitance, which could cause an unwanted

gate voltage spike. An internal circuit holds GATE low before

the internal circuitry wakes up. This reduces the FET current

surges substantially at insertion. The GATE pin is also held low

during the initial timing cycle, and until the ON pin has been

taken high to start the hotswap operation.

During hotswap operation the GATE pin is first pulled up by a

12 μA current source. If the current through the sense resistor

reaches the overcurrent fault timing threshold, Voctim, then a

pull-up current of 60 µA on the TIMER pin is turned on, and

this pin starts charging up. At a slightly higher voltage in the

sense resistor, the error amplifier servos the GATE pin to

maintain a constant current to the load by controlling the

voltage across the sense resistor to the linear current limit, VLIM.

A normal hotswap will complete when the board supply

capacitors near full charge and the current through the sense

resistor drops, to eventually reach the level of the board load

current. As soon as the current drops below the overcurrent

fault timing threshold, the current into the TIMER pin will

switch from being a 60 μA pull-up to a 100 μA pull-down. The

ADM1177 will then drive the GATE voltage as high as it can to

fully enhance the FET and reduce RON losses to a minimum.

A hotswap will fail if the load current fails to drop below the

overcurrent fault timing threshold, VOCTIM, before the TIMER

pin has charged up to 1.3 V. In this case the GATE pin is then

pulled down with a 2 mA current sink. The GATE pull-down

will stay on until a hotswap retry starts, which can be forced by

de-asserting then re-asserting the ON pin, or the device will

retry automatically after a cool-down period, on the ADM1177-

1.

The ADM1177 also features a method of protection from

sudden load current surges, such as a low impedance fault,

when the current seen across the sense resistor may go well

beyond the linear current limit. If the fast overcurrent trip

threshold, VOCFAST, is exceeded, the 2 mA GATE pull-down is

turned on immediately. This pulls the GATE voltage down

quickly to enable the ADM1177 to limit the length of the

current spike that gets through, and also to bring the current

through the sense resistor back into linear regulation as quickly

as possible. This protects the backplane supply from sustained

overcurrent conditions, which may otherwise have caused

problems with the backplane supply level dropping too low.

CALCULATING CURRENT LIMITS AND FAULT

CURRENT LIMIT TIME

The nominal linear current limit is determined by a sense

resistor connected between the VCC and SENSE pins as given

by the equation below:

ILIMIT(NOM) = VLIM(NOM)/RSENSE = 100 mV/RSENSE

(1)

The minimum linear fault current is given by Equation 2:

ILIMIT(MIN) = VLIM(MIN)/RSENSE(MAX) = 90 mV/RSENSE(MAX)

(2)

The maximum linear fault current is given by Equation 3:

ILIMIT(MAX) = VLIM(MAX)/RSENSE(MIN) = 110 mV/RSENSE(MIN)

(3)

The power rating of the sense resistor should be rated at the

maximum linear fault current level.

The minimum overcurrent fault timing threshold current is

given by

IOCTIM(MIN) = VOCTIM(MIN)/RSENSE(MAX) = 85 mV/RSENSE(MAX)

(4)

The maximum fast overcurrent trip threshold current is given

by

IOCFAST(MAX) = VOCFAST(MAX)/RSENSE(MIN) = 115 mV/RSENSE(MIN)(5)

The fault current limit time is the time that a device will spend

timing an overcurrent fault, and is given by

tFAULT ~= 21.7 × CTIMER ms/μF

(6)

INITIAL TIMING CYCLE

When VCC is first connected to the backplane supply, there is

an internal supply (time-point (1) in Figure 4) in the ADM1177

which needs to charge up. A very short time later (significantly

less than 1 ms) the internal supply will be fully up and, since the

undervoltage lockout voltage has been exceeded at VCC, the

device will come out of reset. During this first short reset period

the GATE pin is held down with a 25 mA pulldown current,

and the TIMER pin is pulled down with a 100 μA current sink.

The ADM1177 then goes through an initial timing cycle. At

point (2) the TIMER pin is pulled high with 5 µA. At time point

(3), the TIMER reaches the VTIMERL threshold and the first

portion of the initial cycle ends. The 100 µA current source

then pulls down the TIMER pin until it reaches 0.2 V at time

Nº de peça semelhante - ADM1177-2ARMZ-R7

Fabricante Electrônico	Nome de Peças	Folha de dados	Descrição Electrónicos
Analog Devices	ADM1177	583Kb / 24P	Hot Swap Controller and Digital Power Monitor with Soft Start Pin REV. C

More results

Descrição semelhante - ADM1177-2ARMZ-R7

Fabricante Electrônico	Nome de Peças	Folha de dados	Descrição Electrónicos
Analog Devices	ADM1177	583Kb / 24P	Hot Swap Controller and Digital Power Monitor with Soft Start Pin REV. C
	ADM1175	693Kb / 24P	Hot Swap Controller and Digital Power Monitor with Convert Pin REV. 0
	ADM1176	683Kb / 24P	Hot Swap Controller and I2C짰 Power Monitor with Convert Pin REV. 0
	ADM1178	203Kb / 16P	Hot Swap Controller and Digital Power Monitor with AlertB Output Rev. PrD May 2006
	ADM1278	874Kb / 61P	Hot Swap Controller and Digital Power and Energy Monitor with PMBus Interface
	EVAL-ADM1275EBZ	741Kb / 48P	Hot-Swap Controller and Digital Power REV. D
	ADM1272	578Kb / 57P	High Voltage Positive Hot Swap Controller and Digital Power Monitor with PMBus
	ADM1170	248Kb / 16P	1.6 V to 16.5 V Hot Swap Controller with Soft Start REV. A
	ADM1170	266Kb / 16P	1.6 V to 16.5 V Hot Swap Controller with Soft Start REV. 0
	LTC4287	2Mb / 77P	High Power Positive Hot Swap Controller with Power Monitor Rev. 0

More results

ADM1177-2ARMZ-R7 Folha de dados(PDF) 8 Page - Analog Devices

ADM1177-2ARMZ-R7 Folha de dados(HTML) 8 Page - Analog Devices

Nº de peça semelhante - ADM1177-2ARMZ-R7

Descrição semelhante - ADM1177-2ARMZ-R7

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Folha de dados Download

Ligação URL