LTC3726IGN datasheet(13/16 Pages) LINER

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LTC3726

3726fb

the LTC3726) can be used as the input to the peak charge

circuit of Figure 2. For lower output voltages, however, it

is normally necessary to use a dedicated bias winding to

generate adequate bias voltage for the LTC3726.

Current Sensing

The LTC3726 provides considerable flexibility in cur-

rent sensing techniques. It supports two main meth-

ods: 1) resistive current sensing and 2) current trans-

former current sensing. Resistive current sensing is

generally simpler, smaller and less expensive, while

current transformer sensing is more efficient and gen-

erally appropriate for higher (> 20A) output currents.

For resistive current sensing, the sense resistor may

be placed in any one of three different locations: high

side inductor, low side inductor or low side switch, as

shown in Figure 3. Sensing the inductor current (high

side or low side) is generally less noisy but dissipates

more power than sensing the switch current (Figures

3a and 3b). High side inductor current sensing pro-

vides a more convenient layout than low side (no split

ground plane), but can only be used for output volt-

ages up to 5.5V, due to the common mode limitations

of the current sense inputs (IS+ and IS–). For most

applications, low side switch current sensing will be a

good solution (Figure 3c).

For high current applications where efficiency (power

dissipation) is very important, a current sense trans-

former may be used. As shown in Figure 3d, the IS– pin

should be tied off to VCC when a current sense transformer

is used. This causes the IS+ pin to become a single ended

(nondifferential) current sense input with a maximum

current sense voltage of 1.28V. Figure 3d shows a typical

application circuit using a current transformer.

APPLICATIO S I FOR ATIO

LTC3726

78mV MAX

–

3726 F03c

••

LTC3726

78mV MAX

–

3726 F03a

••

Figure 3a. High Side Inductor:

Easier Layout, Low Noise, Accurate

LTC3726

78mV MAX

–

3726 F03b

••

Figure 3b. Low Side Inductor:

Accurate, Low Noise, High VOUT Capable

LTC3726

VCC

1.28V MAX

TRIP

Ω TO

Ω

–

3726 F03d

••

•

Figure 3d. Current Transformer:

Highest Efficiency, High VOUT Capable

Figure 3c. Switch Current Sensing: Easy Layout, Accurate,

Higher Efficiency, High VOUT Capable

Figure 3. Current Sensing Techniques

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