SBOA530 November   2021 TLV9001

 

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Design Goals

InputOutputSupply
VIVo

Iout

VccVeemaxVeemin

–5.5 V < Vee < –4.5 V

–3 V

600 mA

0 V

–4.5 V

–5.5 V

Design Description

This design accurately steps down a voltage level and holds it stable at a fixed output voltage (low dropout regulator). The regulator takes a –4.5-V to –5.5-V input voltage and steps it down to a –3-V rail that supplies current up to 600 mA.

Design Notes

  1. Use the op amp in a linear operating region. Ensure that the inputs of the op amp do not exceed the common-mode range of the device. Linear output swing is usually specified under the AOL test conditions.
  2. The common-mode voltage is equal to the inverting input voltage, set by the TLV431 reference of –1.24 V.
  3. Using a high-gain BJT reduces the output current requirement for the op amp.
  4. The majority of the power loss is |Vee – Vout| × Iout and will be dissipated in transistor T1. A larger Vee will increase power loss and the temperature of T1.
  5. Other op amps may be used in place of the TLV9002, but may require adjustment of the feedback stabilization.
  6. Positive feedback to the amplifier is used, because an inversion is performed by T1.

Design Steps

The transfer function of the circuit is:

Vout=-1.24 V×R1+R2R2
  1. Based on the desired output voltage, in this case -3V, select a ratio of R1 and R2 that satisfies the above equation.
    -3 V=-1.24 V×R1+R2R21.419×R2=R1

    Selecting standard resistors, choose 1.02 kΩ and 715 Ω.


  2. For sizing the output capacitance, the product of C2 and Resr should generate a zero below 10 kHz to ensure stability. The ESR zero is located at:
    Fz(ESR)=12πResrC2=12π(1 Ω)(47×10-6F)=3.38 kHz

Design Results

DC Analysis Results

Vee Sweep
Output Current Sweep
Dropout Voltage

AC Analysis Results

Bode 60 mA
Bode 600 mA

Transient Analysis Results

Transient Response (100-mA Step)

Design References

See the Analog Engineer’s Circuit Cookbooks for TI’s comprehensive circuit library.

AN-1482 LDO Regulator Stability Using Ceramic Output Capacitors

Space-Grade, 100-krad, –2.5-V, Discrete Negative LDO Linear Regulator Circuit

For more information on many op amp topics including common-mode range, output swing, and bandwidth, please visit TI Precision Labs.

Design Featured Devices

TLV9001
Vss1.8 V–5.5 V
VinCMRail-to-rail
VoutRail-to-rail
Vos0.4 mV
Iq0.06 mA
Ib5 pA
UGBW1 MHz
SR2 V/μs
#Channels1
TLV9001

Design Alternative Devices

OPA392
Vss1.7V–5.5V
VinCMRail-to-rail
VoutRail-to-rail
Vos1 μV
Iq1.22 mA
Ib0.01 pA
UGBW13 MHz
SR4.5 V/μs
#Channels1
OPA392