rt9218b Richtek Technology Corporation, rt9218b Datasheet - Page 11

• Manufacturer Part Number: rt9218b
• Description: Synchronous Buck Dc-dc Linear Power Controller
• Manufacturer: Richtek Technology Corporation

OPS (Over Current Setting, VIN_POR and Shutdown)
1.OCP
Sense the low-side MOSFET's R
Connecting a resistor (R
the over-current trip point. R
converter over-current trip point (I
OPS pin function is similar to RC charging or discharging circuit, so the over-current trip point is very sensitive to parasitic
capacitance (ex. shut-down MOSFET) and the duty ratio.
Below Figures say those effect. And test conditions are Rocset = 15kΩ (over -current trip point = 20.6A), Low-side
MOSFET is IR3707.
DS9218B-09 March 2007
V
V
V
V
IN
OUT
IN
OUT
= 5V, V
= 12V, V
= 1.5V
= 1.5V
CC
CC
= 12V
Time (2.5μs/Div)
= 12V
Time (5μs/Div)
OCSET
OCSET
OCP
OCP
) from this pin to the source of the upper MOSFET and the drain of the lower MOSFET sets
, an internal 40μA current source, and the lower MOSFET on resistance, R
DS(ON)
OCSET
UGATE (10V/Div)
UGATE (10V/Div)
) according to the following equation :
to set over-current trip point.
I
OCSET
I
I
L
L
(10A/Div)
(10A/Div)
=
R
DS(ON)
40uA
of
×
the
R
OCSET
lower
−
MOSFET
0.4V
V
V
V
V
IN
OUT
IN
OUT
OPS (200mV/Div)
= 5V, V
= 12V, V
= 1.5V
= 1.5V
CC
CC
= 12V
Time (2.5μs/Div)
= 12V
Time (5μs/Div)
OCP
OCP
RT9218B
OPS
(200mV/Div)
I
I
www.richtek.com
L
L
UGATE
(10V/Div)
UGATE
(10V/Div)
(10A/Div)
(10A/Div)
DS(ON)
, set the
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