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RT6203B Datasheet(HTML) 19 Page - Richtek Technology Corporation

Part No. RT6203B
Description  5A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter with VID Control
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Maker  RICHTEK [Richtek Technology Corporation]
Homepage  http://www.richtek.com
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RT6203B Datasheet(HTML) 19 Page - Richtek Technology Corporation

 
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RT6203B
19
DS6203B-01 July 2017
www.richtek.com
©
Copyright 2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
Output Voltage Setting
The output voltage is set by a resistive divider from the
output to ground with the midpoint connected to FB. The
resistive divider allows the FB pin to sense a fraction of
the output voltage as shown in Figure 1, and the output
voltage can be calculated by the following equation :
Figure 1. Output Voltage Setting
RT6203B
GND
FB
R1
R2
VOUT
OUT
R1
V0.8V (1 +
)
R2

The placement of resistive divider components should be
within 5mm of the FB pin. In order to minimize the power
consumption at light loads and reduce the noise injected
from FB pin, The suggested value of R2 is between 10k
Ω
and 100k
Ω. For output voltage accuracy, use divider
resistors with 1% or better tolerance.
Enable Operation (EN)
EN is a high voltage input pin. For automatic start-up, the
EN pin can be connected to VIN directly. The inherent
hysteresis makes EN useful as a simple timing delay. To
add an additional time delay, the EN pin can be connected
to GND through a capacitor CEN, as shown in Figure 2.
The additional time delay for switching operation to start
can be calculated with the EN's internal logic threshold.
(typically 2V).
An external MOSFET can be added to implement an logic-
controlled EN pin, as shown in Figure 3. The MOSFET
Q1 can provide the logic control on the EN pin, pulling it
down. To prevent enabling circuit when VIN is smaller than
the VOUT target value or some other desired voltage level,
a resistive divider can be placed to control the EN voltage
as the additional input under voltage lockout function, as
shown in Figure 4.
Figure 2. Enable Timing Control
Figure 3. Logic Control for the EN Pin
Figure 4. Resistor Divider for Lockout Threshold Setting
RT6203B
EN
GND
Q1
Enable
RT6203B
EN
GND
VIN
REN1
REN2
RT6203B
GND
EN
CEN
External Soft-Start Function
The RT6203B provides an adjustable soft-start function.
The soft-start function is used to prevent large inrush
current while the converter is being powered-up. The soft-
start timing is the output voltage rising time from 0V to
settled level and can be programmed by the external
capacitor between the SS and GNDpins. An internal current
source ISS (typically, 6
μA) charges the external capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start. The typical soft-
start time can be calculated as follows :
SS
T
SS
SS
SS
C(nF)
V
Soft-Start Time t
(ms) =
I
( A)
C(nF)
1.3
=
6A
For example, If a 10nF capacitor is used, the typical soft-
start will be 2.16ms. Do not leave SS unconnected.
Power-Good Output
The PGOOD pin is an open-drain power-good output and
requires an external pull-up resistor, connected to an
external supply or the on-chip PVCC output. When the


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