ADP3121
PIN CONNECTIONS
BST
IN
OD
VCC
DRVH
SWN
PGND
DRVL
12V
ADP3121
IN 2
VCC
4
DELAY
LATCH
R1
R2 Q
S
OD 3
CMP
1V
CMP
VCC
6
CONTROL
LOGIC
DELAY
D1
BST
1
CBST1
8
DRVH
SW
7
CBST2
RG
RBST
Q1
TO
INDUCTOR
DRVL
5
Q2
PGND
6
Figure 1. Block Diagram
PIN FUNCTION DESCRIPTION
Pin No.
Pin Name
Description
1
BST
Upper MOSFET Floating Bootstrap Supply. A capacitor connected between the BST and SW pins
holds this bootstrapped voltage for the high−side MOSFET while it is switching.
2
IN
Logic Level PWM Input. This pin has primary control of the drive outputs. In normal operation, pulling
this pin low turns on the low−side driver; pulling it high turns on the high−side driver.
3
OD
Output Disable. When low, this pin disables normal operation, forcing DRVH and DRVL low.
4
VCC
Input Supply. This pin should be bypassed to PGND with an ~1 mF ceramic capacitor.
5
DRVL
Synchronous Rectifier Drive. Output drive for the lower (synchronous rectifier) MOSFET.
6
PGND
Power Ground. This pin should be closely connected to the source of the lower MOSFET.
7
SW
Switch Node Connection. This pin is connected to the buck switching node, close to the upper
MOSFET source. It is the floating return for the upper MOSFET drive signal. It is also used to monitor
the switched voltage to prevent the lower MOSFET from turning on until the voltage is below ~1 V.
8
DRVH
Buck Drive. Output drive for the upper (buck) MOSFET.
http://onsemi.com
2