MP28265 – 5A, 21V, SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS
MP28265 Rev. 0.92 www.MonolithicPower.com 4
12/2/2009 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2009 MPS. All Rights Reserved.
PIN FUNCTIONS
Pin # Name Description
1 IN
Supply Voltage. The MP28265 operates from a +4.5V to +21V input rail. C1 is
needed to decouple the input rail. Use wide PCB traces and multiple vias to make
the connection.
2,3,4,5 SW Switch Output. Use wide PCB traces and multiple vias to make the connection.
6 BST
Bootstrap. A capacitor connected between SW and BS pins is required to form a
floating supply across the high-side switch driver.
7 EN/SYNC
EN=1 to enable the chip. External clock can be applied to EN pin for changing
switching frequency. For automatic start-up, connect EN pin to VIN by proper EN
resistor divider as Figure 2 shows.
8 FB
Feedback. An external resistor divider from the output to GND, tapped to the FB
pin, sets the output voltage. To prevent current limit run away during a short circuit
fault condition the frequency fold-back comparator lowers the oscillator frequency
when the FB voltage is below 500mV.
9 PG
Power Good Output, the output of this pin is open drain. Power good threshold is
90% low to high and 70% high to low of regulation value.
10,
Exposed Pad
NC No Internal Connection.
11 VCC
Bias Supply. Decouple with 0.1uF~0.22uF cap. And the capacitance should be no
more than 0.22uF.
12,13 GND
System Ground. This pin is the reference ground of the regulated output voltage.
For this reason care must be taken in PCB layout.
14 AGND
Signal Ground. AGND is not internally connected to System Ground, make sure
AGND connected to system Ground in PCB layout.
