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Data Sheet

LT3097

APPLICATIONS INFORMATION

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The LT3097 is a dual, positive and negative, high-performance,

low-dropout, linear regulator that features Analog Devices, Inc., ul-

tra-low noise and ultra-high PSRR architecture for powering noise-

sensitive applications. Designed as a precision-current source fol-

lowed by a high-performance, rail-to-rail voltage buffer, the LT3097

can provide rail-to-rail output voltages, 0 V to 15 V for the positive

output and 0 V to –19.5 V for the negative output. The LT3097 also

features a programmable current limit, fast start-up capability, and

programmable power good for both positive and negative sides.

The LT3097 is simple to use and incorporates all the protection

features expected in high-performance regulators. Short-circuit pro-

tection, safe-operating area protection, and thermal shutdown with

hysteresis for both positive and negatives sides are included. The

positive regulator also includes reverse-battery protection and re-

verse-current protection.

The LT3097 is available in a thermally enhanced, low-profile 22-

lead 6 mm × 3 mm, Plastic DFN package with exposed backside

pads for each regulator, providing optimum thermal performance.

OUTPUT VOLTAGE

The LT3097 positive regulator incorporates a precision 100 μA

current reference flowing out of the SETP pin, which also connects

to the inverting input of the error amplifier of the positive regula-

tor. Similarly, the LT3097 negative regulator incorporates precision

100 μA current reference flowing into the SETN pin, which also

connects to the inverting input of the error amplifier of the negative

regulator. Figure 124 illustrates that connecting resistors from SETP

to the ground and from SETN to the ground generates reference

voltages for the respective error amplifiers. These reference voltag-

es are the product of the SETP pin current and the SETP pin

resistor for the positive regulator, and the product of the SETN

pin current and the SETN pin resistor for the negative regulator.

The unity-gain configuration of the error amplifiers produces low-im-

pedance versions of these voltages on the noninverting inputs of

the error amplifiers, that are, the OUTSP pin, which is externally

connected to the OUTP pin for the positive regulator; and the

OUTSN pin, which is externally connected to the OUTN pin for the

negative regulator.

Figure 124. Basic Adjustable Regulator

The rail-to-rail error amplifier and current reference of the positive

regulator allow for a wide output voltage range from 0 V (using

a 0 Ω resistor) to VINP minus dropout, up to 15 V. A PNP-based

input pair is active for a 0 V to 0.6 V output and an NPN-based

input pair is active for output voltages greater than 1.3 V, with a

smooth transition between the two input pairs from 0.6 V to 1.3 V

output. While the NPN-based input pair is designed to offer the best

overall performance for the positive regulator, see the Table 1 for

details on the offset voltage, SETP pin current, output noise, and

PSRR variation with the error-amplifier input pair. The rail-to-rail

error amplifier and current reference of the negative regulator allow

for a wide output voltage range from 0 V (using a 0 Ω resistor)

to VINN minus dropout, up to –19.5 V. An NPN-based input pair is

active for a 0 V to –0.8 V output and a PNP-based input pair is

active for output voltages less than –1.5 V, with a smooth transition

between the two input pairs from –0.8 V to –1.5 V output. While the

PNP-based input pair is designed to offer the best overall perform-

ance for the negative regulator, see the Table 1 for details on the

offset voltage, SETN pin current, output noise, and PSRR variation

with the error-amplifier input pair. Table 4 lists many common output

voltages and their corresponding 1% RSETP and RSETN resistors.

Table 4. 1% Resistor for Common Output Voltages

RSETP/RSETN (kΩ)

VOUTP (V)

VOUTN (V)

24.9

2.5

–2.5

33.2

3.3

–3.3

49.9

–5

121

–12

150

–15

The benefit of using a current reference compared to the typical

voltage reference used in conventional regulators is that the regu-

lator always operates in a unity-gain configuration, independent

of the programmed output voltage. This configuration allows the

positive and the negative regulators of the LT3097 to have loop

gain, frequency response, and bandwidth independent of the output

voltage. As a result, noise, PSRR, and transient performance do

not change with output voltage. Moreover, because none of the er-

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