PAM2320 View Datasheet(PDF) - Power Analog Micoelectronics
Part Name
Description
MFG CO.
'PAM2320' PDF : 11 Pages View PDF
PAM2320
3A Low Noise Step-Down DC-DC Converter
For the condition where the step-down converter
is in dropout at 100% duty cycle, the total device
dissipation reduces to:
PD =IO2 RDSON H +IQVIN
Since R , DS(ON) quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range. The maximum power dissipation
depends on the thermal resistance of IC
package, PCB layout, the rate of surrounding
airflow and temperature difference between
junction and ambient. The maximum power
dissipation can be calculated by the following
formula:
Where TJ(max)
PD
=
TJ(MAX)
θ
-TA
JA
is the maximum
allowable
junction temperature 125°C.TA is the ambient
temperature and θJA is the thermal resistance
from the junction to the ambient. Based on the
standard JEDEC for a two layers thermal test
board, the thermal resistance θJA of SOP-8(EP)
90°C/W respec tively. The maximum power
dissipation at TA = 25°C can be calculated by
following formula:
P D=(125°C-25°C)/90°C/W=1.11W(SOP-8)
Setting the Output Voltage
The internal reference is 0.6V (Typical). The
output voltage is calculated as below:
The output voltage is given by Table 1.
V O=0.6×1+
R1
R2
Table 1: Resistor recommend for output voltage
setting
Vo
R1
R2
1.2V
150k
150k
1.5V
225k
150k
1.8V
300k
150k
2.5V
475k
150k
3.3V
680k
150k
100% Duty Cycle Operation
As the input voltage approaches the output
voltage, the converter turns the P-channel
transistor continuously on. In this mode the
output voltage is equal to the input voltage minus
the voltage drop across the P - channel
transistor:
V OUT = V IN – I LOAD (R dson + R L)
where Rdson = P-channel switch ON resistance,
ILOAD = Output current, RL = Inductor DC
resistance
UVLO and Soft-Start
The reference and the circuit remain reset until
the VIN crosses its UVLO threshold.
The PAM2320 has an internal soft-start circuit
that limits the in-rush current during start-up.
This prevents possible voltage drops of the input
voltage and eliminates the output voltage
overshoot. The soft-start make the output voltage
rise up smoothly.
Short Circuit Protection
The switch peak current is limited cycle-by-cycle
to a typical value of 4A. In the event of an output
voltage short circuit, the device operates with a
frequency of 500kHz and minimum duty cycle,
therefore the average input current is more
smaller than current limit.
Thermal Shutdown
When the die temperature exceeds 150°C, a
reset occurs and the reset remains until the
temperature decrease to 120°C, at which time
the circuit can be restarted.
Power Analog Microelectronics, Inc
www.poweranalog.com
9
05/2011 Rev1.0
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