How to manage the power supply of mobile devices with high accuracy
In addition to being smaller, thinner, and lighter, user’s demand to power supply management of mobile devices which are becoming high functionality is increasingly severer. LDO regulators are often used when high accuracy power supply voltages are required. When selecting an LDO regulator, it cannot be judged only by the output voltage accuracy described in the data sheet. Characteristics such as ripple rejection ratio and load transient response must be checked. Toshiba's TCR5BM and TCR8BM series provide a stable power supply for mobile devices by devising circuit configurations to achieve high accuracy output voltages, while delivering low dropout voltages.
Load transient response and ripple rejection ratio
The load current connected to the output of the LDO regulator may increase or decrease suddenly. At this time, the output voltage may also fluctuate temporarily, and when the fluctuation is large, it may cause adverse effects such as malfunction or stop of the equipment. The load transient response is represented by the peak value of the fluctuation appearing in the output voltage for a stepwise change in the output current, indicating that the smaller the value, the more stable the voltage can be supplied.
The power supply line also has voltage fluctuations with various frequency components due to the operation of the various devices connected to the line. For power supply ICs, voltage fluctuations superimposed on the input power line become a problem. These fluctuations are called the ripple voltage, and the LDO regulator is characterized by suppressing the propagation of the ripple voltage superimposed on the input voltage to the output side. The ripple rejection ratio is the value that represents this characteristic.
TCR5BM/8BM series has improved load transient response and ripple rejection ratio. It has excellent response performance against sudden current changes and provides stable constant voltage operation with minimal voltage fluctuation. In addition, excellent ripple rejection ratio is achieved in a wide frequency range by optimizing the gain of each frequency band, etc.
With these features, TCR5BM/8BM can minimize the effects of load current fluctuations and input noise on the output, and provides a stable output voltage as the load side power supply.
Refer to following link for the details of load transient response and ripple rejection ratio.
Dropout voltage characteristics
TCR5BM/8BM series also improves dropout voltages, in addition to load transient response and ripple rejection ratio.
A voltage higher than the input voltage is applied to the bias terminal separated from the input terminal, and drives the gate of the built-in output MOSFET so that the difference between the input voltage and the output voltage can be reduced.
The LDO regulator is buck-type, so normally set the input voltage higher than the output. Since the dropout voltage is also a limit value at which the drop in the input voltage does not affect the output voltage, it can be said that the output voltage is configured to be less susceptible to input fluctuations.
The power consumption of the regulator itself is the difference between the input and output voltages multiplied by the output current. Reducing the difference between the input and output voltages also reduces power consumption that causes heat generation. This can reduce or eliminate heat generation measures such as securing space and attaching a heat sink, and helps reduce the size and weight of the mounting set.
Refer to following link for the details of dropout voltage and power consumption.
Recommended product list
Product Number |
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|---|---|---|---|---|---|
Data sheet |
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Package name, dimensions (mm), outline drawing |
DFN5B
|
DFN5B
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Operating range |
Output voltage (V) |
0.8 to 3.6 |
0.8 to 3.6 |
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Output current (A) |
0 to 0.5 |
0 to 0.8 |
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Electrical Characteristics |
Bias current (μA) |
Max |
@IOUT=0 mA, VBIAS terminal current |
36 |
36 |
Max |
@IOUT=0 mA, VIN terminal current |
6 |
6 |
||
Dropout voltage (mV) |
Max |
@IOUT=500 mA, VOUT=1.1 V, TCR5BM |
140 |
- |
|
Max |
@IOUT=800 mA, VOUT=1.1 V, TCR8BM |
- |
245 |
||
Ripple compressibility (dB) |
Typ. |
@IOUT=10 mA, f=1 kHz, VIN Ripple=200 mVp-p, VOUT=0.8 V |
98 |
98 |
|
Load transient response (mV) |
Typ. |
@IOUT=1 mA → |
-100 |
-100 |
|
Typ. |
@IOUT = Max output current → |
100 |
100 |
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