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PDF RT9921 Data sheet ( Hoja de datos )
| Número de pieza | RT9921 | |
| Descripción | Integrated Multi-Channel DC-DC Converter | |
| Fabricantes | Richtek Technology Corporation | |
| Logotipo |  |
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Preliminary
RT9921
Integrated Multi-Channel DC-DC Converter
for TFT LCD Panels
General Description
The RT9921 includes a high-performance boost regulator,
a low dropout linear regulator (LDO), a gate pulse
modulator (GPM), a voltage detector, a VCOM buffer (unity-
gain OPA), and a VGH charge pump controller for active-
matrix thin-film transistor (TFT) liquid-crystal displays
(LCDs).
The boost converter provides the regulated supply voltage
for the panel source driver ICs. The converter is a high
switching frequency (640kHz or 1.2MHz) current-mode
regulator with an integrated 16VN-Channel 0.2Ω MOSFET
that allows the use of ultra-small inductors and ceramic
capacitors. It provides fast transient response to pulsed
loading while achieving efficiency over 90%. The device
can produce output voltage as high as 15V from an input
as low as 2.5V. Soft-Start is programmed by external
capacitor, which sets the input-current ramp-rate.
The low-dropout (LDO) linear regulator can supply up to
350mA current while input voltage is 3.3V. It uses an
internal PMOS as the pass device. It is suitable for the
supply voltage of the timing controller.
The GPM is controlled by frame signals from timing
controller to modulate the Gate-On voltage, VGHM, which
acts a flicker compensation circuit to reduce the coupling
effect between gate lines and pixels. It also can delay the
Gate-On voltage while power-on for achieving a corrected
power-on sequence for gate driver ICs. Both of power-on
delay time and the falling time of the Gate-On voltage are
programmable by external capacitor and resistor.
The voltage detector monitors the supply voltage to issue
a reset signal while the detected voltage is too low. The
detecting level is decided by an external resistor divider
and the delay time is programmable by an external
capacitor.
The VCOM buffer can drive the LCD VCOM voltage that
features high short-circuit current (140mA), fast slew rate
(12V/μs), wide bandwidth (12MHz) and rail-to-rail inputs
and outputs.
The VGH charge pump controller provides regulated TFT
Gate-On voltage. The regulation of the positive charge
pump is generated by the internal comparator that senses
the output voltage and compares it with an internal
reference.
Features
z 2.5V to 5.5V Input Supply Voltage
z 640kHz/1.2MHz Current-Mode Boost Regulator
`Fast Transient Response to Pulsed Load
`Adjustable Output Voltage (±1%)
`Built-In 16V, 2A, 0.2Ω N-MOSFET
`High Efficiency Up to 90%
`Programmable Soft-Start
`Over-Current Protection
`Output Under-Voltage Protection
z Low Dropout Voltage Linear Regulator
`Adjustable Output Voltage : 1.5V to VIN − 0.5V
( ±1.5%)
`Maximum Output Current : 350mA
On-Chip GPM Controller with Adjustablehttp://www.DataSheet4U.net/
z
`Falling Time and Power-On Delay
`Flicker Compensator
`Power-On Sequence Control
z Low Voltage Detector
`Programmable Detecting Voltage (±2%) and Delay
Time
z Unity-Gain Operation Amplifier for VCOM Buffer
z Charge Pump for VGH regulation
z Over-Temperature Protection
z Thin 24 Lead VQFN Package
z RoHS Compliant and 100% Lead (Pb)-Free
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
DS9921-00 November 2007
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
Preliminary
RT9921
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage, VIN ---------------------------------------------------------------------------------------- −0.3 to 6.5V
z LX --------------------------------------------------------------------------------------------------------------------- −0.3 to 16V
z VGH, VGHM, RE -------------------------------------------------------------------------------------------------- −0.3 to 30V
z AVDD ----------------------------------------------------------------------------------------------------------------- −0.3 to 16V
z VGH − AVDD, VGHM − AVDD ---------------------------------------------------------------------------------- −0.3 to 20V
z OPAI, OPAO, DRVP ---------------------------------------------------------------------------------------------- −0.3 to (VAVDD + 0.3V)
z VDPM, VFLK, CD, RESET, VDIV, SS, COMP, FB, FBP ------------------------------------------------ −0.3 to (VIN + 0.3V)
z LDOI ------------------------------------------------------------------------------------------------------------------ −0.3 to 6.5V
z ADJ, LDOO --------------------------------------------------------------------------------------------------------- −0.3 to (LDOI+0.3V)
z Power Dissipation, PD @ TA = 25°C
VQFN-24L 4x4 ----------------------------------------------------------------------------------------------------- 1.786W
z Package Thermal Resistance (Note 4)
VQFN-24L 4x4, θJA ------------------------------------------------------------------------------------------------ 56°C/W
z Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260°C
z Junction Temperature --------------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range ------------------------------------------------------------------------------------ −65°C to 150°C
z ESD Susceptibility (Note 2)
HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions (Note 3)
z Maximum Output Voltage Setting, AVDD and VOUT ------------------------------------------------------ 15V
z Maximum (VGH − AVDD) --------------------------------------------------------------------------------------- 18V
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z Junction Temperature Range ------------------------------------------------------------------------------------ −40°C to 125°C
z Ambient Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(VIN = 3.3V, VOUT = 8.5V, TA = 25°C, unless otherwise specification)
Par amete r
Sy mbol
Test Condition
System Supply
Input Supply Voltage
VIN
VIN Under Voltage Lockout
Threshold
VUVLO
VIN Rising
Hy ste resi s
VIN Quiescent Current
Shutdown Current
Main Boost Regulator
IQ
ISHDN
VFB = 1.3V, LX no Switching
VFB = 1.1V, LX Switching
VIN = 3.3V
Operation Frequency
Maximum Duty Cycle
fOSC
FREQ = 0
FREQ = VIN
Min Typ Max Units
2.5 -- 5.5 V
1.8 2 2.2
-- 0.1 --
V
-- 0.5 1 mA
-- 2
4 mA
-- 1
5 μA
-- 640 -- kHz
1 1.2 1.5 MHz
86 90 -- %
To be continued
DS9921-00 November 2007
www.richtek.com
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
Preliminary
RT9921
Application Information
The RT9921 contains a high performance boost regulator
to generate voltage for output voltage, gate-on driver and
gate-off driver. It also includes of a high-current rail-to rail
operation amplifier, a gate pulse modulator (GPM), a
programmable timing control voltage detector, and a low
dropout linear regulator. The following content contains
the detailed description and the information of the
component selection.
Boost Regulator
The boost regulator is a high efficiency current-mode PWM
architecture with 640k / 1.2MHz operation frequency. It
performs fast transient responses to generate source driver
supplies for TFT LCD display. The high operation frequency
allows smaller components to minimize the thickness of
LCD panel. To regulate the output voltage is to set resistive
voltage-divider sensing at FB pin. The error amplifier varies
the COMP voltage by sensing the FB pin to regulate the
output voltage. For better stability, the slope compensation
signal that combined with the current-sense signal will
be compared with the COMP voltage to determine the
current trip point and duty cycle.
Soft-Start
The RT9921 provides soft-start function to minimize the
inrush current. When power on, an internal constant current
charges an external capacitor. The rising voltage rate on
COMP pin will be limited during the charging period and
the inductor peak current will also be limited at the same
time. In the meanwhile, the frequency increases slowly at
the beginning. When power off, the external capacitor will
be discharged for next soft start time.
The soft-start function is implemented by the external
capacitor with a 4μA constant current charging to the
softstart capacitor. Therefore, the capacitor should be large
enough for output voltage regulation. Typical value for
softstart capacitor range is 27nF. The available soft start
capacitor range is from 10nF to 100nF.
Output Voltage
The regulated output voltage is calculated by the following
formula :
VOUT
=
VFB × ⎛⎜⎝1+
R1
R2
⎞⎟⎠,
where
VFB
=
1.24V
(typ.)
The recommended value for R2 should be up to 100kΩ
without some sacrificing. To place the resistor-divider as
close as possible to the chip can reduce noise sensitivity.
Loop Compensation
The voltage feedback loop can be compensated with an
external compensation network consisted of R3, C3 (As
Figure 1). Choosing R3 to set high frequency integrator
gain for fast transient response and C3 to set the integrator
zero to maintain loop stability. For typical application
VIN = 3.3V , VOUT = 8.5V , COUT = 4.7μF x 3 , L = 4.7μH,
the recommened value for compensation is as below :
R3 = 56kΩ, C3 = 1nF.
Over Current Protection
The RT9921 main boost converter has the function of over-
current from protection to limit peak inductor current. It
prevents large current damaging the inductor and diode.
During the ON-time, once the inductor current exceeds
the current limit, the internal LX switch turns off
immediately and shortens the duty cycle. Therefore, the
output voltage drops if the over-current condition occurs.
Actual current limit is always larger than the nominal value
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because of the internal circuit delay. Current limit is also
affected by the input voltage, duty cycle, and inductor
value.
Over Temperature Protection
The RT9921 main boost converter has thermal protection
function to prevent the excessive power dissipation from
overheating. When the junction temperature exceeds
170°C, it will shut down the device. Once the device cools
down by approximately 20°C, it will start to operate
normally. For continuous operation, do not operate over
the maximum junction temperature rating around 150°C.
Under Voltage Protection
If the boost regulator feedback voltage is under 90% of
the nominal value, the RT9921 activates an internal timer.
If the fault condition continues for 160ms, the PWM will
latch off and won't restart until VIN power is cycled. The
under-voltage protection is disabled during the soft-start
time.
DS9921-00 November 2007
www.richtek.com
11
datasheet
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