
MP1567 – 1.2A SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER 
MP1567 Rev. 2.3 
1/3/2006 
www.MonolithicPower.com 
4
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 2006 MPS. All Rights Reserved. 
TM
PIN FUNCTIONS 
Pin# 
Name 
Function 
Power Switch Boost. BS powers the gate of the high-side N-Channel power MOSFET switch. 
Connect a 10nF or greater capacitor between BS and SW. 
Internal Power Input. IN supplies the power to the MP1567 through the internal LDO 
regulator. Bypass IN to PGND with a 10μF or greater capacitor. Connect IN to the input 
source voltage. 
Output Switching Node. SW is the source of the high-side N-Channel switch and the drain of 
the low-side N-Channel switch. Connect the output LC filter between SW and the output. 
Power Ground. PGND is the source of the N-Channel MOSFET synchronous rectifier. 
Connect PGND to SGND as close to the MP1567 as possible. 
SGND Signal Ground. 
Soft-Start Input. Place a capacitor from SS to SGND to set the soft-start period. The MP1567 
sources 2μA from SS to the soft-start capacitor at start up. As the voltage at SS rises, the 
feedback threshold voltage increases to limit inrush current at start up. 
Feedback Input. FB is the inverting input of the internal error amplifier. Connect a resistive 
voltage divider from the output voltage to FB to set the output voltage. 
Compensation Node. COMP is the output of the error amplifier. Connect a series RC network 
to compensate the regulation control loop. 
Internal 2.4V Regulator Bypass. Connect a 10nF capacitor between BP and SGND to bypass 
the internal regulator. Do not apply any load to BP. 
On/Off Control Input. Drive EN high to turn on the MP1567; low to turn it off. For automatic 
startup, connect EN to IN. 
1 
BS 
2 
IN 
3 
SW 
4 
PGND 
5 
6 
SS 
7 
FB 
8 
COMP 
9 
BP 
10 
EN 
OPERATION 
The MP1567 measures the output voltage 
through an external resistive voltage divider and 
compares that to the internal 0.9V reference to 
generate the error voltage at COMP. The 
current-mode regulator uses the voltage at 
COMP and compares it to the inductor current 
to regulate the output voltage. The use of 
current-mode regulation improves transient 
response and improves control loop stability. 
At the beginning of each cycle, the high-side 
N-Channel MOSFET is turned on, forcing the 
inductor current to rise. The current at the drain 
of 
the 
high-side 
MOSFET 
measured and converted to a voltage by the 
current sense amplifier. That voltage is 
compared to the error voltage at COMP. When 
the inductor current raises sufficiently, the PWM 
comparator turns off the high-side switch and 
turns on the low-side switch, forcing the 
is 
internally 
inductor current to decrease. The average 
inductor current is controlled by the voltage at 
COMP, which in turn, is controlled by the output 
voltage. Thus the output voltage controls the 
inductor current to satisfy the load. 
Since the high-side N-Channel MOSFET 
requires voltage above V
IN
 to drive its gate, a 
bootstrap capacitor from SW to BS is required 
to drive the high-side MOSFET gate. When SW 
is driven low (through the low-side MOSFET), 
the BS capacitor is internally charged. The 
voltage at BS is applied to the high-side 
MOSFET gate to turn it on, and maintains that 
voltage until the high-side MOSFET is turned 
off and the low-side MOSFET is turned on, and 
the cycle repeats. Connect a 10nF or greater 
capacitor from BS to SW to drive the high-side 
MOSFET gate. Using a larger capacitor does 
little to improve performance.