DS6203B Datasheet, PDF (19/22 Pages) Richtek Technology Corporation – 5A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter with VID Control

RT6203B
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 :
V_OUT
 0.8V (1
+
R1
R2
)
V_OUT
R1
FB
RT6203B
R2
GND
EN
C_EN
RT6203B
GND
Figure 2. Enable Timing Control
Enable
EN
Q1 ^RT6203B
GND
Figure 3. Logic Control for the EN Pin
Figure 1. Output Voltage Setting
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 10kΩ
and 100kΩ. 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 V_IN is smaller than
the V_OUT 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.
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6203B-00 September 2016
V_IN
R_EN1
R_EN2
EN
RT6203B
GND
Figure 4. Resistor Divider for Lockout Threshold Setting
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 GND pins. An internal current
source I_SS (typically, 6μA) 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 :
Soft-Start Time t_SS(ms) =
C_SS (nF)  V_T
I_SS (A)
=
C_SS (nF) 
6 A
1.3
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
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
19