IC Data Sheets
8.
8.5
Diagram
, RT7257ADJ/3A (IC U17)
Figure 8-5 Internal block diagram and pin configuration
19710_
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01_140409.ep
s
140409
Block diagram
Pinning information
RT7257 ADJ/3A
(TOP VIEW)
SOP-8 (Exposed Pad)
BOOT
VIN
SW
GND
SS
EN
FB
COMP
GND
2
3
4
5
6
7
8
9
Pin No.
Pin Name
Pin Function
1 BOOT
Bootstrap for High Side Gate Driver. Connect a 0.1
μ
F or greater ceramic
capacitor from BOOT to SW pins.
2 VIN
Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a
suitable large ceramic capacitor.
3
SW
Switch Node. Connect this pin to an external L-C filter.
4,
9 (Exposed Pad)
GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
5 FB
Feedback Input. It is used to regulate the output of the converter to a set value
via an external resistive voltage divider.
6 COMP
Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.
7 EN
Enable Input. A logic high enables the converter; a logic low forces the
converter into shutdown mode reducing the supply current to less than 3
μ
A.
Attach this pin to VIN with a 100k
Ω
pull up resistor for automatic startup.
8 SS
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor
from SS to GND to set the soft-start period. A 0.1
μ
F capacitor sets the
soft-start period to 13.5ms.
VIN
EN
GND
BOOT
FB
SW
L
R1
R2
V
OUT
V
IN
RT7257
SS
C
SS
COMP
C
C
R
C
C
BOOT
C
IN
C
OUT
R
EN
