RT2862
Function Block Diagram
VIN
V
CC
Internal
Regulator
Shutdown
Comparator
1.2V
V
A
V
CC
+
-
Oscillator
Foldback
Control
0.4V
+
Slope Comp
Current Sense
Amplifier
+
-
R
SENSE
VA
EN
5k
Ω
Lockout
Comparator
-
+
1.7V
UV
S
+
-
Current
Comparator
BOOT
Q
SW
R
Q
GND
-
UV
Comparator
3.6V
SS
0.8V
+
+
EA
-
RT
FB
COMP
Operation
The RT2862 is a constant frequency, current-mode
synchronous step-down converter. In normal operation,
the high-side N-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. While the high-side
N-MOSFET is turned off, the low-side N-MOSFET is turned
on to conduct the inductor current until next cycle begins.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (V
FB
) with the internal 0.8V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, and then the
error amplifier's output voltage rises to allow higher inductor
current to match the load current.
Oscillator
The oscillator frequency can be set by using an external
resister R
T
. Oscillator frequency range is from 300kHz to
1MHz.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high-
side gate driver.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
Enable
The converter is turned on when the EN pin is higher than
2V. When the EN pin is lower than 0.4V, the converter will
enter shutdown mode and reduce the supply current to
0.5µA.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 2ms.
UV Comparator
If the feedback voltage is lower than 0.4V, the UV
Comparator will go high to turn off the high-side MOSFET.
The output under voltage protection is designed to operate
in hiccup mode. When the UV condition is removed, the
converter will resume switching.
Thermal Shutdown
The over-temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 20°C, the converter will
automatically resume switching.
is a registered trademark of Richtek Technology Corporation.
DS2862-02 January 2018
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
