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

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LTC2928I

Multichannel Power Supply Sequencer and Supervisor

Linear Technology 

LTC2928

Applications Information

Should multiple channels fault simultaneously, the re-

ported channel is given priority according to the channel

number (1,2,3,4).

In the event of an external fault, the LTC2928 fault manager

reports overvoltage channels to the fault channel outputs

(CMP3, CMP4). If no channel is overvoltage, the default

report is channel 4 (High, High). As such, in certain ap-

plications, a potential reporting ambiguity exists.

Operating without Pass Transistors

The LTC2928 enable outputs may directly drive the shut-

down/enable, run/soft-start or control inputs on DC/DC

converters. However, since the LTC2928 enable outputs

may drive to a relatively high voltage with low current

(10µA), care must be taken not to exceed the maximum

voltage rating on the DC/DC converter enable input. The

gate voltage available from the LTC2928 enable output

ranges between VCC + 4.5V to VCC + 6V. Use a resistor

to limit an enable output to an external supply voltage. A

resistor between 4.7k and 27k is recommended.

nections are allowed to exist within one system (Figure 4).

It is important not to corrupt these communication lines

with added passive or active loads.

CAS Connection: Supply Extension

When more than four supplies need to be synchronized

in time, use the CAS connection. Consider the application

in Figure 1. This application allows for 8 supplies in 8

distinct time positions, or all at once depending upon the

choice of RT resistors. The upper device is designated as

master and the lower device is the slave. Both LTC2928s

are configured as “FIRST” and “LAST” and the CAS pins

are tied together.

(MASTER/FIRST)

LTC2928

ON

VCC

VCC

RT1

RT2

DONE

RT3

RT4

STMR

CAS

Cascading Multiple LTC2928s

LTC2928s can be cascaded in two ways, simultaneously.

The first method, time extension, allows an unlimited

number of supplies to be sequenced in additional time

positions. The second method, supply extension, allows

additional supplies to be sequenced in the same time po-

sition. The examples below demonstrate how to achieve

time and supply extension.

Central to configuring a cascade application is the assign-

ment of LTC2928 properties such as master/slave and

first/not-first/last status. Master/Slave and first/not-first

designation is made with the MS1 and MS2 three-state

configuration inputs (see Table 2). An LTC2928 is con-

figured as “LAST” by pulling DONE to VCC with a 2.4k to

5.1k resistor.

Next, the appropriate connection of one or both bidirectional

communication lines must be made. To achieve supply

extension, the CAS pins between master and slave devices

are tied together (Figure 1). To achieve time extension, the

DONE pin of the preceding LTC2928 is connected to the

ON pin of the subsequent LTC2928 (Figure 2). Both con-

CAS

ON

VCC

VCC

RT1

RT2

DONE

RT3

RT4

LTC2928

(SLAVE/FIRST)

2928 F01

Figure 1. Using the CAS pin to

synchronize additional power supplies

(slave STMR is not used).

The master controls the sequencing. The time delay be-

tween adjacent positions is configured with a capacitor

on the master’s STMR pin and the slave STMR is ignored.

After application of the ON signal to start the sequence-up

phase, the CAS pin pulls low, enabling any supply config-

ured for time position 1. After supplies in time position 1

cross their sequence-up threshold, CAS is released and

pulled high. If no supplies are configured for a particular

time position, CAS pulls high after 25µs. CAS remains

high for one STMR period (100µs minimum) and then

For more information www.linear.com/LTC2928

2928fa

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