1A Ultra Low Dropout Linear Regulator
TJ3964
Output Capacitor
The TJ3964 requires a proper output capacitance to maintain stability and improve transient response
over current. The ESR of the output capacitor within the limits of 0.5ꢀ to 10ꢀ is required. A minimum
capacitance value of 22µF of tantalum or aluminum electrolytic capacitor is recommended. In a case of
ceramic capacitor, a minimum capacitance value of 10µF is required and additional resistance of
minimum 1ꢀ should be added with the output capacitor in series to maintain its minimum ESR. The
resistance and capacitance have to be varied upon the load current.
VOUT
ADJ
OUTPUT
VOUT
ADJ
OUTPUT
R2
R1
R2
R1
+
Additional Resistance
22µF
-
GND
GND
10µF
Maximum Output Current Capability
The TJ3964 can deliver a continuous current of 1A over the full operating junction temperature range.
However, the output current is limited by the restriction of power dissipation which differs from packages.
A heat sink may be required depending on the maximum power dissipation and maximum ambient
temperature of application. With respect to the applied package, the maximum output current of 1A may
be still undeliverable due to the restriction of the power dissipation of TJ3964. Under all possible
conditions, the junction temperature must be within the range specified under operating conditions.
The temperatures over the device are given by:
TC = TA + PD X θCA
/ TJ = TC + PD X θJC / TJ = TA + PD X θJA
where TJ is the junction temperature, TC is the case temperature, TA is the ambient temperature, PD is the
total power dissipation of the device, θCA is the thermal resistance of case-to-ambient, θJC is the thermal
resistance of junction-to-case, and θJA is the thermal resistance of junction to ambient.
The total power dissipation of the device is given by:
PD = PIN – POUT = (VIN X IIN)–(VOUT X IOUT
)
= (VIN X (IOUT+IGND)) – (VOUT X IOUT) = (VIN - VOUT) X IOUT + VIN X IGND
where IGND is the operating ground current of the device which is specified at the Electrical Characteristics.
The maximum allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax
)
of the application, and the maximum allowable junction temperature (TJmax):
TRmax = TJmax – TAmax
The maximum allowable value for junction-to-ambient thermal resistance, θJA, can be calculated using the
formula:
θ
JA = TRmax / PD = (TJmax – TAmax) / PD
TJ3964 is available in SOT23-5, SOT-223, TO-252 and SOP-8 packages. The thermal resistance
depends on amount of copper area or heat sink, and on air flow. If the maximum allowable value of θJA
calculated above is as described in Table 1, no heat sink is needed since the package can dissipate
enough heat to satisfy these requirements. If the value for allowable θJA falls near or below these limits, a
heat sink or proper area of copper plane is required.
Dec. 2009 – Rev. 1.1
- 9 -
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
