Plus and Minus 35V LDOs Support Bi-Polar Analog Apps

Oct 1, 2010 12:00 PM
By Sam Davis, Editor-in-Chief

Two low dropout regulators for powering precision bi-polar analog circuits improve efficiency and accuracy in noise-sensitive applications.

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TEXAS INSTRUMENTS Incorporated has introduced the TPS7A30, a -36V low dropout regulator (LDO), which is the first of its kind. Soon to be released is its positive voltage counterpart, the TPS7A49. Together, they will provide a low-noise, bi-polar power solution for precision analog applications. These LDOs are intended for use with test equipment; industrial, networking and telecom equipment; base stations; microwave and radio links; noise filtering for receive, transmit and power amplifiers; and medical applications.

The TPS7A30 can source a maximum load of -200 mA, whereas the TPS7A49 can source a maximum load of 150 mA. Input voltage range for the TPS7A49 is +3.0V to +36V, and the TPS7A30 has a -3.0V to -36V input range. These two linear regulators are stable with any output capacitance greater than 2.2 µF. The TPS7A49 and TPS7A30 can be configured as adjustable versions with an output voltage range as listed in the table, which also lists the dropout voltage for the two LDOs.

These linear regulators include a CMOS logic-level-compatible enable pin and capacitor-programmable soft-start function that allows customized power-management schemes. Other available features include built-in current limit and thermal shutdown protection to safeguard the device and system during fault conditions.

The figure shows a TPS54260 driving TPS7A30 and TPS7A49 LDOs to produce +12V and -12V. Use of a bypass capacitor, CBYPASS, on pin 6 of the TPS7A30 and TPS7A49 (NR/SS) reduces output noise. Typical switching frequency of the TPS54260 is 300 kHz.

The TPS54260 is a 60V, 2.5A, step-down regulator IC with an integrated high side power MOSFET. Current mode control provides simple external compensation and flexible component selection. A low ripple pulse skip mode reduces the no load, regulated output supply current to 138µA. Setting the enable pin low reduces the supply current to 1.3µA.

The regulator provides low output noise when a noise reduction capacitor (C_NR/SS) is used. The capacitor serves as a filter for the internal reference. By using a 0.01µF noise reduction capacitor, the output noise is reduced by almost 80%.

In addition, the noise reduction capacitor achieves up to 20 dB of additional power-supply rejection for frequencies between 110Hz and 400 kHz.

The TPS7A30 and TPS7A49 regulator ICS are both available now in MSOP-8 PowerPADTM packaging and are priced at $1.50 and $1.10, respectively, in quantities of 1,000. The TPS7A30_49EVM-567 evaluation module is available and priced at $20.

TABLE: TPS7A30 AND TPS7A49 CHARACTERISTICS AT T_J = -40°C to 125°C

PARAMETER	TPS7A30	TPS7A49
QUIESCENT CURRENT (IQ)	-55 µA (typical)	61 µA (typical)
INPUT VOLTAGE RANGE (VIN)	-3.0V to -36V	3.0V to 36V
MAXIMUM OUTPUT (IOUT)	-200 mA	150 mA
NOMINAL OUTPUT ACCURACY (Min./Max.)	+2.5 % max./-2.5% min. over load, line and temperature	+2.5 % max./-2.5% min. over load, line and temperature
OUTPUT NOISE (TYPICAL)	17.5µVRMS, 10 Hz to 100kHz, VIN = -6.2V, VOUT = -5.0V, CBYPASS = 10nF, CIN = 2.2µF, COUT = 2.2 µF	21.15µVRMS, 10 Hz to 100kHz, VIN = 6.2V, VOUT = 5.0V, CBYPASS = 10nF, CIN = 2.2µF, COUT = 2.2 µF
PSRR (TYPICAL)	72 dB @ 120 Hz, VIN = -6.2V, VOUT = -5.0V, CBYPASS = 10nF CIN = 2.2µF, COUT = 2.2 µF	72 dB @ 120 Hz, VIN = 6.2V, VOUT = 5.0V, CBYPASS = 10nF CIN = 2.2µF, COUT = 2.2 µF
ADJUSTABLE OUTPUT VOLTAGE RANGE (VOUT)	-1.184V to -33V (typical)	1.194V to 33V (typical)
DROPOUT VOLTAGE (VDO) (Typical)	-325mV @ IOUT = -200 mA, -216 mV @ IOUT = -100 mA	260 mV @ IOUT = 100 mA 333 mV @ IOUT = 150 mA

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