MP1583 – 3A, 23V, 385KHz STEP-DOWN CONVERTER
PIN FUNCTIONS (continued)
Pin # Name Description
Enable/UVLO. A voltage greater than 2.71V enables operation. For complete low
current shutdown the EN pin voltage needs to be at less than 900mV. When the
voltage on EN exceeds 1.2V, the internal regulator will be enabled and the soft-start
capacitor will begin to charge. The MP1583 will start switching after the EN pin
voltage reaches 2.71V. There is 7V zener connected between EN and GND. If EN is
driven by external signal, the voltage should never exceed 7V.
7
8
EN
SS
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to
set the soft-start period. To disable the soft-start feature, leave SS unconnected.
OPERATION
The MP1583 is a current-mode step-down
regulator. It regulates input voltages from 4.75V to
23V down to an output voltage as low as 1.222V,
and is able to supply up to 3A of load current.
The voltage at COMP is compared to the
internally measured switch current to control the
output voltage.
The converter uses an internal N-Channel
MOSFET switch to step-down the input voltage to
the regulated output voltage. Since the MOSFET
requires a gate voltage greater than the input
voltage, a boost capacitor connected between
SW and BS drives the gate. The capacitor is
internally charged when SW is low.
The MP1583 uses current-mode control to
regulate the output voltage. The output voltage is
measured at FB through a resistive voltage
divider and amplified through the internal error
amplifier.
The
output
current
of
the
transconductance error amplifier is presented at
COMP where a RC network compensates the
regulation control system.
An internal 10ꢀ switch from SW to GND is used
to insure that SW is pulled to GND when SW is
low in order to fully charge the BS capacitor.
2
IN
CURRENT
SENSE
AMPLIFIER
INTERNAL
REGULATORS
+
--
5V
OSCILLATOR
Σ
SLOPE
COMP
1
3
BS
40/385KHz
CLK
+
--
+
S
R
Q
Q
SW
CURRENT
COMPARATOR
SHUTDOWN
COMPARATOR
--
1.2V
1μ A
7
EN
LOCKOUT
7V
--
COMPARATOR
--
+
1.8V
2.54V
+
4
GND
0.7V 1.222V
5
--
+
FREQUENCY
FOLDBACK
COMPARATOR
ERROR
AMPLIFIER
6
8
FB
GM = 800μ A/V
COMP
SS
Figure 1—Functional Block Diagram
MP1583 Rev. 3.1
6/20/2011
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5
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