RT2862A
Function Block Diagram
VIN
V
CC
Internal
Regulator
Oscillator
Current Sense
Amplifier
R
SENSE
Shutdown
V
A
V
CC
Slope Comp
UV
+
-
Comparator
Foldback
Control
VA
1.2V
+
-
0.4V
+
-
BOOT
SW
Lockout
Comparator
S
Q
Q
UV
5kΩ
Comparator
-
+
EN
+
-
R
1.7V
Current
Comparator
GND
3.6V
0.8V
+
+
-
EA
SS
FB
COMP
RT
Operation
Enable
The RT2862A is a current-mode synchronous step-down
converter. In normal operation, the high-sideN-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.
The converter is turned on when the ENpin is higher than
2V. When the ENpin 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.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (VFB) 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.
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.
Oscillator
The oscillator frequency can be set by using an external
resister RT. Oscillator frequency range is from 300kHz to
1MHz.
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.
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.
©
is a registered trademark of Richtek Technology Corporation.
DS2862A-02 January 2018
www.richtek.com
3
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