LT1620 查看數據表（PDF） - Linear Technology

零件编号

产品描述 (功能)

比赛名单

LT1620

Rail-to-Rail Current Sense Amplifier

Linear Technology 

LT1620/LT1621

APPLICATIONS INFORMATION

reduces battery charging current until the external load

subsides.

In Figure 4 the LT1620 is coupled with an LT1513 SEPIC

battery charger IC to create an input overcurrent protected

charger circuit.

The programming voltage (VCC – VPROG) is set to 1.0V

through a resistor divider (RP1 and RP2) from the 5V input

supply to ground. In this configuration, if the input current

drawn by the battery charger combined with the system

load requirements exceeds a current limit threshold of 3A,

the battery charger current will be reduced by the LT1620

such that the total input supply current is limited to 3A.

Refer to the LT1513 data sheet for additional information.

PROGRAMMING ACCURACY CONSIDERATIONS

PWM Controller Error Amp Maximum Source Current

In a typical battery charger application, the LT1620 con-

trols charge current by servoing the error amplifier output

pin of the associated PWM controller IC. Current mode

control is achieved when the LT1620 sinks all of the

current available from the error amplifier. Since the LT1620

has finite transconductance, the voltage required to gen-

erate its necessary output current translates to input

offset error. The LT1620 is designed for a typical IOUT sink

current of 130µA to help reduce this term. Knowing the

current source capability of the associated PWM control-

ler in a given application will enable adjustment of the

required programming voltage to accommodate the de-

sired charge current. A plot of typical VPROG voltage offset

vs PWM source capability is shown in Figure 5a. For

example, the LTC1435 has a current source capability of

about 75µA. This translates to about –15mV of induced

programming offset at VPROG (the absolute voltage at the

PROG pin must be 15mV lower).

VCC – VPROG Programmed Voltage ≠ 0.8V

The LT1620 sense amplifier circuit has an inherent input

referred 3mV offset when IN+ – IN– = 0V to insure closed-

loop operation during light load conditions. This offset vs

input voltage has a linear characteristic, crossing 0V as

IN+ – IN– = 80mV. The offset is translated to the AVG

output (times a factor of 10), and thus to the programming

voltage VPROG. A plot of typical VPROG offset voltage vs

IN+ – IN– is pictured in Figure 5b. For example, if the

desired load current corresponds to 100mV across the

sense resistor, the typical offset, at VPROG is 7.5mV (the

absolute voltage at the PROG pin must be 7.5mV higher).

This error term should be taken into consideration when

using VID values significantly away from 80mV.

VCC – VPROG2 Programmed Voltage ≠ 1.6V

(LT1620GN Only)

The offset term described above for VPROG also affects the

VPROG2 programming voltage proportionally (times an addi-

tional factor of 2). However, VPROG2 voltage is typically set

well below the zero offset point of 1.6V, so adjustment for this

term is usually required. A plot of typical VPROG2 offset

voltage vs IN+ – IN– is pictured in Figure 5c. For example,

setting the VPROG2 voltage to correspond to IN+ – IN– = 15mV

typically requires an additional –50mV offset (the absolute

voltage at the PROG2 pin must be 50mV lower).

Sense Amplifier Input Common Mode < (VCC – 0.5V)

The LT1620 sense amplifier has additional input offset

tolerance when the inputs are pulled significantly below

the VCC supply. The amplifier can induce additional input

referred offset of up to 11mV when the inputs are at 0V

common-mode. This additional offset term reduces roughly

linearly to zero when VCM is about VCC – 0.5V. In typical

applications, this offset increases the charge current tol-

erance for “cold start” conditions until VBAT moves away

from ground. The resulting output current shift is generally

negative; however, this offset is not precisely controlled.

Precision operation should not be attempted with sense

amplifier common mode inputs below VCC – 0.5V. Input

referred offset tolerance vs VCM is shown in Figure 5d.

VCC ≠ 5V

The LT1620 sense amplifier induces a small additional

offset when VCC moves away from 5V. This offset follows

a linear characteristic and amounts to about ±0.33mV

(input-referred) over the recommended operating range

of VCC, centered at 5V. This offset is translated to the AVG

and AVG2 outputs (times factors of 10 and 20), and thus

to the programming voltages. A plot of programming

offsets vs VCC is shown in Figure 5e.

8

Share Link: