SC1592 Datasheet, PDF (6/18 Pages) Semtech Corporation – Low Dropout High Performance Adjustable Positive Voltage Regulator

SC1592
POWER MANAGEMENT
Application Information
The SC1592 is a 3A low dropout high performance linear
voltage regulator. The SC1592 can be used for voltage
applications as low as 0.8V and is ideal for down
conversion utilizing dual supply configuration. This allows
for extremely low dropout voltages with excellent load
and line regulation. The SC1592 can be utilized in high
voltage applications, with V_IN and V_CNTL up to 16V, providing
there is adequate thermal management.
SC1592 is designed to meet stringent requirements of
current generation microprocessors and other sensitive
electronic devices. This is possible by employing an
additional bias source, V_CNTL. The voltage of this supply
needs to be at least 1.5V greater than the output voltage
in order to achieve low dropout, typically less then
300mV.
Unlike most of the other high current linear regulators,
the SC1592 provides a programmable current limit which
can be set with a single resistor. The value of the
programming resistor is:
+3.3V Vcntl
C1
2.2uF
+2.5V Vin
C2
22uF
CNTL
OUT
SC1592
IN
10k ^EN
GND
SENSE
ILIM
R1
100
V_OUT
= (1+
R2
R3
)
•
V_REF
V_REF = 0.8V typ.
Figure 2
+1.8V Vout
R2
66.5
C3
100uF
R3
53
The circuit in Figure 2 shows a typical application of 2.5V
to 1.8V conversion with a 3.3V control supply and the
load range of up to 3A steady state. Considering the
approximate 2W power being dissipated by the pass
element of the SC1592, we are still able to choose an
SO-8 EDP package with T_JA = 36.5°C/W mount on the
1sq.in. copper pad allocated for adequate heat transfer.
I_LIM
≈
240 • V_OUT
R_LIM
where I_LIM = selected current limit value
V_OUT = regulated output voltage
R_LIM = programmable current limit resistor
The SC1592 has a fast transient response that allows it
to handle large load changes associated with high current
applications. Proper selection of the of the output
capacitor and it’s ESR value determines stable operation
and optimizes performance.
The ambient temperature in this case should not exceed
50°C. If this temperature range is too restrictive, then
the DDPAK can be utilized, having T_JA = 29°C/W mount
on the same size copper pad.
Input capacitor: A minimum of 10µF ceramic capacitor
is recommended to be placed directly next to the Vin pin.
This allows for the device being some distance from any
bulk capacitance on the rail. Additionally, bulk
capacitance may be added closely to the input supply
pin of the SC1592 to ensure that Vin does not sag,
improving load transient response.
The typical application shown in Figure 2 was tested with
a wide range of different capacitors. The circuit was found
to be unconditionally stable with capacitor values from
47µF to 330µF and ESR ranging from 0.5mΩ to greater
then 75mΩ.
It’s recommended to maintain 5-10mA through the output
divider network in order to have a tight load and line
regulation. Initial accuracy of the internal voltage
reference V_REF = 0.8V ±1% over full temperature range.
This commands the use of 0.5% or better accuracy
resistors to build a precision power supply.
Output capacitor: A minimum bulk capacitance of 33µF,
along with a 0.1µF ceramic decoupling capacitor is
recommended. Increasing the bulk capacitance will
improve the overall transient response. The use of
multiple lower value ceramic capacitors in parallel to
achieve the desired bulk capacitance will not cause
stability issues. Although designed for use with ceramic
output capacitors, the SC1592 is extremely tolerant of
output capacitor ESR values and thus will also work
comfortably with tantalum output capacitors.
 2004 Semtech Corp.
6
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