LTC2903 データシートの表示（PDF） - Linear Technology

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LTC2903

Precision Quad Supply Monitor in 6-Lead SOT-23

Linear Technology 

LTC2903-1

APPLICATIO S I FOR ATIO

Power-Up

The LTC2903-1 issues a logic low on the RST output when

an input supply voltage resides below the prescribed

threshold voltage. 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 LTC2903-1 power supply supervisors incorporate

a new low voltage pull-down circuit that can hold the RST

line low with as little as 200mV of input supply voltage on

V1, V2 or V3. The pull-down circuit helps maintain a low

impedance path to ground, reducing the risk of floating the

RST node to undetermined voltages. Such voltages may

trigger external logic causing erroneous reset operation(s).

Furthermore, a mid-scale voltage 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.

When V1, V2 and V3 are ramped simultaneously, the reset

pull-down current increases up to three times the current

that may be pulled with a single input. Figure 1 demon-

strates the reset pin current sinking ability for single

supply and triple supply-tracking applications. Figure 2

shows a detailed view of the reset pin voltage with a 10k

pull-up resistor to V1.

The LTC2903-1 supervisors derive their internal supply

voltage (VCC) automatically from the greater voltage on the

V1 and V2 inputs. With all supply inputs above threshold,

the quiescent current drawn from VCC is 20µA (typ).

10000

TA = 25°C

VRST = 0.3VCC

1000

Supply Monitoring

The LTC2903-1 accurately monitors four inputs in a small

6-lead SOT-23 package. The low voltage reset output

includes an integrated 200ms reset delay timer. The reset

line pulls high 200ms after all voltage inputs exceed their

respective thresholds. The reset output remains low dur-

ing power-up, power-down and brownout conditions on

any of the voltage inputs.

For applications requiring an adjustable trip threshold, use

the V4 input on the LTC2903-A1. Connect the tap point on

an external resistive divider (R1, R2) placed between the

positive voltage being sensed and ground, to the high

impedance input on V4. The LTC2903-A1 compares the

voltage on the V4 pin to the internal 0.5V reference.

Figure␣ 3 shows a generic setup for the positive adjustable

application.

0.7 TA = 25°C

0.6

0.5

COMPETITION

PART

0.4

0.3

0.2

V1 ONLY

V1 = V2 = V3

0.1

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

V1 (V)

39031 F02

Figure 2. RST Output Voltage with a 10k Pull-Up to V1

(Enlarged Area of Detail)

100 V1 = V2 = V3

V1 ONLY

10

1

0 0.2 0.4 0.6 0.8 1.0 1.2

VCC (V)

29031 F01

Figure 1. RST Pull-Down Current vs VCC

10

VTRIP

R1

1%

V4

R2

1%

LTC2903-A1

–

+

0.5V +–

29031 F03

Figure 3. Setting the Positive Adjustable Trip Point

29031f

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