RT2810A/B
Output Under-Voltage Protection
Hiccup Mode
Through extra resister RLIM connect to RLIM pin to setting
the current limit value as Figure 7, below offer approximate
formula equation for design reference :
1
The RT2810AH/RT2810BH provides Hiccup Mode Under-
Voltage Protection (UVP). When the FB voltage drops
below 70% of the feedback reference voltage, the output
voltage drops below the UVP trip threshold for longer than
250μs (typical) then IC's UVP is triggered. UVP function
will be triggered to shut down switching operation. If the
UVP condition remains for a period, the RT2810 will retry
automatically. When the UVP condition is removed, the
converter will resume operation. The UVP is disabled
during soft-start period.
RLIM
=
ILIM 106 5.588107
Current Limit vs. RLIM
16
15
14
13
12
11
10
9
Latch Mode
For the RT2810AL/RT2810BL, it provides Latch-Off Mode
Under Voltage Protection (UVP). When the FB voltage
drops below 70% of the feedback reference voltage, the
output voltage drops below the UVP trip threshold for longer
than 250μs (typical) then IC's UVP is triggered. UVP
function will be triggered to shut down switching operation.
In shutdown condition, the RT2810 can be reset by EN
pin or power input VIN.
8
7
6
65 75 85 95 105 115 125 135 145 155 165 175 185
RLIM (k
)
Ω
Figure 7. Current Limit vs. RLIM
Output Over-Voltage Protection
If the output voltage VOUT rises above the regulation level
and lower 1.2 times regulation level, the high-side switch
naturally remains off and the synchronous rectifier turns
on. For RT2810BL, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches the low side current limit. If the output voltage
still remains high, then IC's switches remain that the
synchronous rectifier turns on and high-side MOS keeps
off to operate at typical 500kHz switching protection, again
if inductor current reaches low side current limit, the
synchronous rectifier will turn off until next protection
clock. If the output voltage exceeds the OVP trip threshold
(1.2 times regulation level) for longer than 5μs (typical),
then IC's output Over-Voltage Protection (OVP) is
triggered. RT2810BL chip enters latch mode.
Current Limit
The RT2810 current limit is a cycle-by-cycle “valley” type,
measuring the inductor current through the synchronous
rectifier during the off-time while the inductor current ramps
down. The current is determined by measuring the voltage
between source and drain of the synchronous rectifier. If
the inductor current exceeds the current limit, the on-
time one-shot is inhibited (Mask high side signal) until
the inductor current ramps down below the current limit.
Thus, only when the inductor current is well below the
current limit is another on time permitted. This arrangement
prevents the average output current from greatly exceeding
the guaranteed current limit value, as typically occurs with
other valley-type current limits. If the output current
exceeds the available inductor current (controlled by the
current limit mechanism), the output voltage will drop. If it
drops below the output under-voltage protection level, the
IC will enter UVP protection.
For RT2810AL, if the output voltage VOUT rises above the
regulation level and lower 1.2 times regulation level, the
high-side switch naturally remains off and the synchronous
rectifier turns on until the inductor current reaches zero
current. If the output voltage remains high, then IC's
switches remain off. If the output voltage exceeds the OVP
The current limit of low side MOSFET is adjustable by an
external resistor connected to the RLIM pin. The current
limit range is from 6A to 16A.
Copyright 2016 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
www.richtek.com
14
DS2810A/B-06 November 2016
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
