LT1787HVCMS8 datasheet(10/12 Pages) LINER

10 / 12 page

LT1787/LT1787HV

Figure 8. Unidirectional Current Sensing Mode

Figure 7. Single Supply 2.5V Bidirectional Operation

with External Voltage Reference and I/V Converter

2.5V

µF

RSENSE

ISENSE

2.5V + VSENSE(MAX)

CHARGER/

LOAD

VOUT A

1787 F07

LT1495

1000pF

LT1389-1.25

2.5V

–

LT1787

FIL+

FIL–

VBIAS

VOUT

–

DNC

VEE

ROUT

1787 F08

0.1

µF

RSENSE

2.5V TO

60V

VOUT

LOAD

LT1787HV

FIL+

FIL–

VBIAS

VOUT

–

DNC

VEE

ROUT

+ – V

– (V)

0.30

0.25

0.20

0.15

0.10

0.05

0.005 0.010

IDEAL

0.015 0.020

1787 F09

0.025 0.030

Figure 9. Expanded Scale of Unidirectional Output

Buffered Output Operation

Figure 7 shows the LT1787’s outputs buffered by an

operational amplifier configured as an I/V converter. This

configuration is ideal for monitoring very low voltage

supplies. The LT1787’s VOUT pin is held equal to the

reference voltage appearing at the op amp’s noninverting

input. This allows monitoring VS supplies as low as 2.5V.

The op amp’s output may swing from ground to its

positive supply voltage. The low impedance output of the

op amp may drive following circuitry more effectively than

the high output impedance of the LT1787. The I/V con-

verter configuration also works well with split supply

voltages.

Single Supply Unidirectional Operation

Figure 8 shows the simplest connection in which the

LT1787 may be used. The VBIAS pin is connected to

ground, and the VOUT pin swings positive with increasing

sense current. The LT1787’s outputs can swing as low as

30mV as shown in Figure 9. Accuracy is sacrificed at small

output levels, but this is not a limitation in protection

circuit applications or where sensed currents do not vary

greatly. Increased low level accuracy can be obtained by

level shifting VBIAS above ground. The level shifting may

be done with resistor dividers, voltage references or a

simple diode. Accuracy is ensured if the output signal is

sensed differentially between VBIAS and VOUT.

APPLICATIONS INFORMATION

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