MP2259 – 1A, 16V, 1.4MHz STEP-DOWN CONVERTER
OPERATION
The MP2259 is a current mode buck regulator.
with EA output voltage proportional to the peak
inductor current.
At the beginning of a cycle, M1 is off. The EA
output voltage is higher than the current sense
amplifier output, and the current comparator’s
output is low. The rising edge of the 1.4MHz
CLK signal sets the RS Flip-Flop. Its output
turns on M1 then connects the SW pin and
inductor to the input supply.
The increasing inductor current is sensed and
amplified by the Current Sense Amplifier. Ramp
compensation is summed to Current Sense
Amplifier output and compared to the Error
Amplifier output by the PWM Comparator.
When the sum of the Current Sense Amplifier
output and the Slope Compensation signal
exceeds the EA output voltage, the RS Flip-
Flop is reset and M1 is turned off. The external
Schottky rectifier diode (D1) conducts the
inductor current.
If the sum of the Current Sense Amplifier output
and the Slope Compensation signal does not
exceed the EA output for a whole cycle, then
the falling edge of the CLK resets the Flip-Flop.
The output of the Error Amplifier integrates the
voltage difference between the feedback and
the 0.8V bandgap reference. The polarity is
such that a FB pin voltage lower than 0.8V
increases the EA output voltage. Since the EA
output voltage is proportional to the peak
inductor current, an increase in its voltage
increases current delivered to the output.
IN 5
+
--
1
EN 4
REGULATOR
OSCILLATOR
1.4MHz
x20
CURRENT SENSE
AMPLIFIER
REGULATOR
BST
S
+
--
1pF
CURRENT
LIMIT
COMPARATOR
Q
DRIVER
M1
6
SW
R
R
REFERENCE
27pF
+
EA
--
+
--
FB 3
GND 2
ERROR
AMPLIFIER
PWM
COMPARATOR
MP2259_F01_BD01
Figure 1—Functional Block Diagram
MP2259 Rev. 0.92
9/15/2011
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