LTC2908 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

LTC2908

Precision Six Input Supply Monitor

Linear Technology 

LTC2908

APPLICATIONS INFORMATION

Supply Monitoring

The LTC2908 is a low power, high accuracy, six input

supply monitoring circuit with two adjustable inputs. The

reset delay is set to a nominal of 200ms with an internal

capacitor, eliminating the need for an external timing

capacitor.

All input voltages must be above predetermined thresholds

for the reset not to be invoked. The LTC2908 asserts the

reset output during power-up, power-down and brownout

conditions on any one of the voltage inputs.

Ultralow Voltage Pull-Down on RST

The LTC2908 issues a logic low on the RST output when

any one of the inputs falls below its threshold. Ideally, the

RST logic output would remain low with the input supply

voltage down to zero volts. Most supervisors lack pull-

down capability below 1V.

The LTC2908 power supply supervisor incorporates a novel

low voltage pull-down circuit that can hold the RST line low

with as little as 200mV of input supply voltage on V1 and/or

V2 (see Figures 1 and 2). The pull-down circuit helps maintain

a low impedance path to ground, reducing the risk of the

RST node from floating to an indeterminate voltage.

Such an indeterminate voltage may trigger external logic

causing erroneous reset operation(s). Furthermore, a

mid-scale voltage level could cause external circuits

to operate in the middle of their voltage transfer

characteristic, consuming more quiescent current than

normal. These conditions could cause serious system

reliability problems.

Power-Up

During power-up, RST starts asserting low as soon as

there is at least 200mV on V1 and/or V2. The RST pull-

down capability is a function of V1 and V2 as shown in

the Typical Performance Characteristics.

The greater of V1, V2 is the internal supply voltage (VCC)

that powers the other internal circuitry. Once all the VX

inputs rise above their thresholds, an internal timer is

started. After the internal timer counts a 200ms delay

time, RST weakly pulls high to VCC.

Power-Down

On power-down, once any of the VX inputs drop below

their threshold, RST asserts logic low. VCC of at least 0.5V

guarantees a logic low of 0.15V at RST.

10

VCC = V1 = V2

V3 = V4 = VADJ1 = VADJ2 = GND

1

RST AT 150mV

0.1

RST AT 50mV

0.01

10

VCC = V1

V2 = V3 = V4 = VADJ1 = VADJ2 =

VADJ3 = VADJ4 = VADJ5 = GND

1

RST AT 150mV

0.1

RST AT 50mV

0.01

0.001

0

0.2

0.4 0.6 0.8

1

SUPPLY VOLTAGE, VCC (V)

2908 G16

Figure 1. RST Pull-Down Current vs

Supply Voltage with 2 Inputs LTC2908-A1/

LTC2908-B1

0.001

0

0.2

0.4

0.6

0.8

1

SUPPLY VOLTAGE, VCC (V)

2908 G17

Figure 2. RST Pull-Down Current vs

Supply Voltage with 1 Input

2908fd

10

Share Link: