LTC2928I データシートの表示（PDF） - Linear Technology

部品番号

コンポーネント説明

メーカー

LTC2928I

Multichannel Power Supply Sequencer and Supervisor

Linear Technology 

LTC2928

Applications Information

Correcting for IR Drops

Sense feedback is common in high current applications.

Parasitic resistance coupled with high currents causes volt-

age drops. The sense pin of a power module is designed

to help regulate the voltage at a point in the distribution

circuitry beyond the voltage drops. The output of the power

module is raised until the desired voltage is achieved at

the sense point. During startup with sense feedback,

large inrush currents may cause the output of the power

module to exceed its maximum output. This may cause

the module to shutdown.

The LTC2928 is easily configured to enable a sense tran-

sistor after a power supply has been sequenced on and

inrush currents have diminished (Figure 7). The sense

transistor feeds the sequenced supply voltage back to the

sense line of the power module. The power module will

raise its output to compensate for voltage drops across

the sequencing transistor and other parasitics.

During the sequence-down phase, the sense transistor will

be disconnected before the supply sequencing transistor.

If the supply transistor were to be disconnected first, the

power module would sense the voltage drop and may

attempt to drive higher in order to compensate.

POWER

MODULE

OUT +

PARASITIC

IOUT

RDS(ON) RESISTANCE VOUT

Discharging Load Capacitance

It is often necessary to discharge load capacitance quickly.

Use the pull-down strength of the LTC2928 enable out-

puts to achieve faster turn-off times. Sequence the en-

able outputs in the same time position (RT resistors are

identical). With the connections shown in Figure 8, EN1 is

used to discharge the load capacitance through its 100Ω

on resistance. If shorter discharge time is required, use

external inverters as shown in Figure 9.

POWER

MODULE

SD

VCC

EN2

EN1

RT1 LTC2928 V1

RT2

V2

VOUT

+

LOAD

2928 F08

Figure 8. Load Capacitance Discharge

POWER

MODULE

SD

VCC

EN2

EN1

RT1 LTC2928 V1

RT2

V2

VOUT

VCC

+

LOAD

IRF530

2N7002

2928 F09

SENSE +

VCC

100Ω

100Ω

EN2 V2 EN1

LTC2928

RT1

V1

RT2

2928 F07

Figure 7. Correcting for IR drops

(RT1 > RT2)

Figure 9. Fast Load Capacitance Discharge

Using the Power Module Voltages to Gate the Sequenced

Supplies

The application shown in Figure 10 demonstrates how the

power module outputs can be enabled and monitored for

compliance, and then passed to various loads. Sequencing

up and down is controlled by the level of the 12V supply.

Sequencing up begins at 10.76V. If the application is

disconnected from the 12V supply, an orderly shutdown

will commence when the 12V supply drops to 10.43V. The

blocking diode (D1) allows the 470µF capacitor (C1) to retain

enough energy to complete the sequence down process.

2928fa

20

For more information www.linear.com/LTC2928

Share Link: