DS6257AB Datasheet, PDF (3/15 Pages) –

Functional Block Diagram
RT6257A/B
BOOT VIN
V_IN
Reg
V_CC
Minoff
VIBIAS
V_REF
OC
Control
UV
V_CC
Ripple
LX _Gen. +
+
Comparator
V_CC
Driver
GND LX
EN
UGATE
LGATE
V_IN
On-Time LX
LX
GND
EN
FB
Operation
The RT6257A/B is a high-efficiency, monolithic
synchronous step-down DC-DC converter that can deliver
up to 6A output current from a 4.5V to 18V input supply.
Using the ACOT control mode can reduce the output
capacitance and perform fast transient response. It can
minimize the component size without additional external
compensation network.
Current Limit
The RT6257A/B 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, adding temperature compensation
for greater accuracy. If the current exceeds the current
limit, the on-time one-shot is inhibited until it drops below
the current limit level. 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 (see next section)
the IC will stop switching to avoid excessive heat.
Hiccup Mode
The RT6257A/B use hiccup mode for UVP. When the
protection function is triggered, the IC will shut down for a
period of time and then attempt to recover automatically.
Hiccup mode allows the circuit to operate safely with low
input current and power dissipation, and then resume
normal operation as soon as the overload or short circuit
is removed.
Input Under-Voltage Lockout
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VIN is lower than the UVLO falling threshold voltage, the
device will be lockout.
Shut-Down, Start-Up and Enable (EN)
The enable input (EN) has a logic-low level. When V_EN is
below this level the IC enters shutdown mode. When V_EN
exceeds its logic-high level the IC is fully operational.
External Bootstrap Capacitor
Connect a 0.1μF low ESR ceramic capacitor between
BOOT and LX. This bootstrap capacitor provides the gate
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6257A/B-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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