RT9986 RICHTEK [Richtek Technology Corporation], RT9986 Datasheet - Page 19

• Manufacturer Part Number: RT9986
• Description: 7-CH DC/DC Converter for DSC
• Manufacturer: RICHTEK [Richtek Technology Corporation]

CH3 : Synchronous Step-Down DC/DC Converter
CH3 operates in fixed frequency PW M mode with
integrated internal MOSFETs and compensation network.
The CH3 step-down converter can be operated at 100%
maximum duty cycle to extend battery operating voltage
range. When the input voltage is close to the output
voltage, the converter enters low dropout mode with low
output ripple.
The output voltage can be set by the following equation :
V
where V
CH4 : Synchronous Step-Down DC/DC Converter
CH4 operates at fixed frequency PWM mode with
integrated internal MOSFETs and compensation network.
The CH4 step-down converter can be operated at 100%
maximum duty cycle to extend battery operating voltage
range. When the input voltage is close to the output
voltage, the converter enters low dropout mode with low
output ripple.
The output voltage can be set by the following equation:
V
where V
CH5 : Synchronous Step-Up DC/DC Converter
CH5 is a high voltage synchronous step-up converter for
CCD positive power. The converter operates at fixed
frequency PWM mode, CCM, DCM, and PSM (pulse skip
mode) with integrated internal MOSFETs, compensation
network and load disconnect function.
The output voltage can be set by the following equation:
V
where V
CH6 : INV DC/DC Converter
This converter integrates an internal P-MOSFET with
internal compensation and needs an external Schottky
diode to provide CCD negative power supply.
The output voltage can be set by the following equation :
V
where R11 and R12 are the feedback resistors connected
DS9986-00 May 2011
OUT_CH3
OUT_CH4
OUT_CH5
OUT_CH6
FB3
FB4
FB5
= (R11 / R12) x (1.2V) + 0.6V
= (1 + R5 / R6) x V
= (1 + R7 / R8) x V
= (1 + R9 / R10) x V
is 0.8V typically.
is 0.8V typically.
is 1.25V typically.
FB3
FB4
FB5
to FB6, 1.2V equals to (V
typical.
Reference Voltage
The RT9986 provides a precise 1.8V reference voltage,
V
ceramic capacitor from the VREF pin to GND. Reference
voltage is enabled by pulling EN6 to logic-high.
Furthermore, this reference voltage is internally pulled to
GND at shutdown.
CH7 : WLED Driver
CH7 is a WLED driver that can operate in either current
source mode or synchronous step-up mode, as determined
by LX7
When CH7 works in current source mode, it sinks an
accurate LED current modulated by EN7 high duty such
that it is easily dimmed from 0mA to 30mA. If CH7 works
in synchronous step-up mode, it integrates synchronous
step-up mode with an internal MOSFET and internal
compensation to output a voltage up to 15V. The LED
current is set via an external resistor and controlled via
the PWM duty on the EN7 pin. Regardless of the mode,
holding EN7 low for more than 32ms will turn off CH7.
In addition, CH7 will be turned on until the CH2 soft-start
is finished.
CH7 WLED Current Dimming Control
If CH7 is in synchronous step-up mode, the WLED current
is set by an external resistor. If CH7 is in current source
mode, the sink current into the FB7 pin is 30mA typically
when EN7 is high. Regardless of the mode, dimming is
always controlled by the duty of pulse-width modulated
signal on the EN7 pin. The PWM dimming duty must be
over 10%.
The average current through WLED can be set by the
following equations :
I
or I
LED
REF
LED
(mA) = [250mV / R (W)] x Duty (%) (for step-up mode)
CH7 Operating Mode
Current Source
Synchronous Step-Up
, with souring capability of 100 A. Connect a 0.1 F
(mA) = 30mA x Duty (%) (for current source mode)
'
s initial voltage level.
Table 1. CH7 WLED setting
REF
V
FB6
) and 0.6V is V
RT9986
LX7
0.25V
www.richtek.com
1V
FB6
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