RT9166B View Datasheet(PDF) - Richtek Technology
Part Name
Description
Manufacturer
RT9166B Datasheet PDF : 9 Pages
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Application Information
Like any linear regulator, the RT9166B requires input and
output decoupling capacitors. These capacitors must be
correctly selected for good performance Please note that
linear regulators have high internal loop gains which
require care in guarding against oscillation caused by
insufficient decoupling capacitance.
Input Capacitor
An input capacitance of 1μF is required between the device
input pin and ground directly (the capacitance may be
increased without limit). The input capacitor must be
located less than 1cm from the device to assure input
stability A lower ESR capacitor allows the use of less
capacitance, while higher ESR type (like aluminum
electrolytic) requires more capacitance.
Capacitor types (aluminum, ceramic and tantalum) can
be mixed in parallel, but the total equivalent input
capacitance/ ESR must be defined as above for stable
operation.
There are no requirements for the ESR on the input
capacitor, but tolerance and temperature coefficient must
be considered when selecting the capacitor to ensure 1μF
capacitance over the entire operating temperature range.
Output Capacitor
The RT9166B is designed specifically to work with very
small ceramic output capacitors. The recommended
minimum capacitance (temperature characteristics X7R
or X5R) is 3.3μF with 10mΩ to 50mΩ range ceramic
capacitor between LDO output and GND for transient
stability.
Higher capacitance helps to improve the transient
response. The output capacitor's ESR is critical because
it forms a zero to provide phase lead which is required for
loop stability.
Input-Output (Dropout) Voltage
A regulator's minimum input-to-output differential voltage
(dropout voltage) determines the lowest usable supply
voltage. In battery-powered systems, this determines the
useful end-of-life battery voltage. Because the device uses
a PMOS, its dropout voltage is a function of drain-to-
RT9166B
source on-resistance, RDS(ON), multiplied by the load
current :
VDROPOUT = VIN − VOUT = RDS(ON) x IOUT
Current Limit
The RT9166B monitors and controls the PMOS gate
voltage, with a minimum limit of the output current at
600mA. The output can be shorted to ground for an
indefinite period of time without damaging the part.
Short-Circuit Protection
The device is short-circuit protected in the event of a peak
over-current condition, such that the short-circuit control
loop rapidly drives the output PMOS pass element off.
Once the power pass element shuts down, the control
loop will rapidly cycle the output on and off until the average
power dissipation causes the thermal shutdown circuit to
respond by cycling to a lower frequency. Please refer to
the section on thermal information for power dissipation
calculations.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA ) / θJA
Where TJ(MAX) is the maximum junction temperature, TA
is the ambient temperature, and θJA is the junction to
ambient thermal resistance.
For recommended operating condition specifications of
RT9166B, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θJA, is layout dependent. For SOT-89
packages, the thermal resistance, θJA, is 118°C/W on a
standard JEDEC 51-7 four-layer thermal test board. The
maximum power dissipation at TA = 25°C can be calculated
by the following formula :
DS9166B-01 April 2011
www.richtek.com
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