MP2492 MPS, MP2492 Datasheet - Page 7

• Manufacturer Part Number: MP2492
• Description: 2a, 55v, 100khz Step-down Converter With Programmable Output Current Limit
• Manufacturer: MPS

OPERATION
The MP2492 is a current mode buck regulator.
That is, the EA output voltage is proportional to
the peak inductor current.
At the beginning of a cycle SW 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 100kHz
CLK signal sets the RS Flip-Flop. Its output
turns on SW thus connecting 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 Current Comparator.
When the Current Sense Amplifier plus Slope
Compensation signal exceeds the EA output
voltage, the RS Flip-Flop is reset and the
MP2492 reverts to its initial SW off state.
MP2492 Rev. 1.0
12/20/2010
SS
FB
ENABLE
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
REGULATOR
MP2492 – 2A, 55V, 100kHz WITH PROGRAMMABLE OUTPUT CURRENT LIMIT
REFERENCE
EN
EN
Figure 1—Function Block Diagram
OSCILLATOR
GENERATOR
100KHz
REGULATOR
RAMP
© 2010 MPS. All Rights Reserved.
72.8pF
72.8pF
POR
www.MonolithicPower.com
2483kΩ
ER
6pF
6pF
4.0V
COMPARATOR
GND
If the Current Sense Amplifier plus Slope
Compensation signal does not exceed the
COMP voltage, 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. An
external Schottky Diode (D1) carries the
inductor current when SW is off.
The output current information is sensed via the
ISP and ISN pins. The sense voltage is set at
100mV. If V
V
the power supply will be set by the FB pin. If
V
will pull down on SS and regulate the output at
a constant current.
CURRENT
ISN
SENSE
LIMIT
COMPARATOR
, is less than 100mV, the output voltage of
REGULATOR
PWM
reaches 100mV, the current limit loop
CURRENT SENSE
R
S
R
SENSE
AMPLIFIER
X13.5
D
Q
, the difference of V
-
SS
DRIVER
20mΩ
RSEN
100mV
ISN
VIN
BST
SW
M1
ISP
ISP
and
7