RT9903BGQV RICHTEK [Richtek Technology Corporation], RT9903BGQV Datasheet - Page 14

• Manufacturer Part Number: RT9903BGQV
• Description: 4 Channel DC/DC Converters IC with High-Efficiency Step-Up
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9903B
Where Gm is the transconductance of error amplifier, and
R
In our design, Gm = 200us, R
and then C
Choose C
Step-3 Calculate R
R
are met.
For example, in our design, if 5% transient droop is
allowed, then the error amplifier moves 0.05 x 1V, or
50mV. The error amplifier output drives 50mV x 200us,
or 10uA across R
We select R
The output capacitor is chosed 40uF to cancel the R
C
load condition.
Reference
The chip has an internal 1V reference voltage, which is
the inputs of the error amplifiers of the CH1, CH2, and
CH4 to compare the difference of feedback voltage. The
reference voltage of CH3 is 0.2V for WLEDs application.
The reference voltage can be set up stably when the
supplied power (V
EN3, EN4 either one) goes high.
Thermal Protection
Thermal protection function is integrated in the chip. When
the chip temperature is higher than 180°C, the controllers
of all channels are shutdown. When the thermal protection
is relieved, the chip operates well again.
www.richtek.com
14
CS
C
C
is calculated such that transient droop requirements
zero, and can sustain stable V
is the current sense amplifier transresistance.
C
C
= 4.7nF.
CS
= 4.34nF from calculation.
= 2.7kΩ to meet the requirements.
C
DD
to provide transient gain.
C
) is above 1.5V, and EN1 (or EN2,
CS
= 0.8V/A, and V
OUT
voltage at heavy
FB
Preliminary
= 1V,
C
DS9903B-07 August 2007