RT9903GQV RICHTEK [Richtek Technology Corporation], RT9903GQV Datasheet - Page 14

• Manufacturer Part Number: RT9903GQV
• Description: 5 Channel DC/DC Converters IC with High-Efficiency Step-Up
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9903
Step-2 Calculate C
Choose f
simplified loop-gain formula.
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.
Charge Pump DC/DC Converter (CH5)
This is a low quiescent negative-voltage charge pump
DC/DC converter, which is enabled by EN2. Output ripple
can be easily suppressed by increasing the capacitance
ratio of C
can apply to negative voltage of CCD.
The maximum output current is determined by the ratio
of C
relationship.
I
The negative output voltage is set by R1 and R2. The
FBCP threshold voltage is 0V.
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14
Loop gain =
Gm x
MAX
C
C
V
F
CP
is calculated such that transient droop requirements
F
zero, and can sustain stable V
CP
= (V
: Schottky diode forward voltage
CS
: Charge pump maximum frequency is 500kHz.
1 + SR C
and C
OUT
is the current sense amplifier transresistance.
INCD
C
SC
C
= 10KHz, and then C
C
= 4.7nF.
CS
and C
= 4.34nF from calculation.
C
− 2V
C
OUT
= 2.7kΩ to meet the requirements.
C
C
. This equation would describe the
CP
F
x
) x C
C
to provide transient gain.
C
. This charge pump DC/DC converter
R
V
V
1
CS
OUT
DD
CP
x (1-D) x
x R
x F
x R
CS
1
CP
2
= 0.8V/A, and V
C
= 1
is calculated from the
OUT
1+SR
voltage at heavy
R
OUT
OUT
C
OUT
FB
x
Preliminary
= 1V,
V
V
OUT
FB
C
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 (VDD) is above 1.5V, and EN1 (or EN2,
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.
Charge-
Driver
Pump
INCD
+
-
FBCP
C
X
C
CP
V
DD
DS9903-07 August 2007
R1
R2
Negative
Voltage
C
Output
OUT