RT8206L RICHTEK [Richtek Technology Corporation], RT8206L Datasheet - Page 21

• Manufacturer Part Number: RT8206L
• Description: High Efficiency, Main Power Supply Controller for Notebook Computers
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Reference and Linear Regulator (REF, LDO and 14V
Charge Pump)
The 2V reference (REF) is accurate within ±1% over the
entire temperature range, making REF useful as a precision
system reference. Bypass REF to GND with as 0.22μF
capacitor. REF can supply up to 50μA for external loads.
Loading REF degrades FBx and output accuracy according
to the REF load-regulation error.
An internal regulator produces a fixed output voltage 5V.
The LDO regulator can supply up to 70mA for external
loads. Bypass LDO with a minimum 4.7μF ceramic
capacitor. When the output voltage of the V
than the switchover threshold, an internal 1.5Ω N-Channel
MOSFET switch connects V
while simultaneously shutting down the internal linear
regulator.
In typical application circuit, the external 14V charge pump
is driven by LGATE1. When LGATE1 is low, D1 charges
C5 sourced from V
a diode drop. When LGATE1 transitions to high, the charge
from C5 will transfer to C6 through D2 and charge it to
V
cycle, C6 will charge C7 to its voltage minus a diode drop
through D3. Finally, C7 charges C8 through D4 when
LGATE1 transitions to high. CP output voltage is :
V
where :
SECFB (RT8206L) is used to monitor the charge pump
via the resistive divider. In an event when SECFB drops
below 2V the controller forces ultrasonic mode operation
which keeps the switching frequency above 25kHz to
maintain charge pump voltage.
Reducing the CP decoupling capacitor and placing a small
ceramic capacitor C19 (10pF to 47pF) in parallel will the
upper leg of the SECFB resistor feedback network, R11,
will also increase the robustness of the charge pump.
Copyright
DS8206L/M-07 June 2012
V
V
LGATE1
CP
LGATE1
D
= V
is the forward diode dropped across the Schottkys
©
plus V
OUT1
2012 Richtek Technology Corporation. All rights reserved.
is the peak voltage of the LGATE1 driver
+2 x V
C5
. As LGATE1 transients low on the next
OUT1
LGATE1
. C5 voltage is equal to V
− 4 x V
OUT1
D
to LDO through BYP
OUT1
OUT1
is higher
minus
(MIN)
Current Limit Setting (I
The RT8206L/M has a cycle-by-cycle current limiting
control. The current limit circuit employs a unique “valley”
current sensing algorithm. If the magnitude of the current
sense signal at PHASEx is above the current limit
threshold, the PWM is not allowed to initiate a new cycle
(Figure 4). The actual peak current is greater than the
current limit threshold by an amount equal to the inductor
ripple current. Therefore, the exact current limit
characteristic and maximum load capability are a function
of the sense resistance, inductor value, battery voltage,
and output voltage.
The RT8206L/M uses the on-resistance of the synchronous
rectifier as the current-sense element. Use the worse-
case maximum value for R
datasheet, and add a margin of 0.5%/°C for the rise in
R
The current limit threshold is adjusted with an external
resistor for the RT8206L/M at ILIMx. The current limit
threshold adjustment range is from 50mV to 200mV. In
the adjustment mode, the current limit threshold voltage
is precise to 1/10 the voltage seen at ILIMx. The threshold
defaults to 100mV when ILIMx is connected to VCC. The
logic threshold for switchover to the 100mV default value
is higher than VCC−1V.
Carefully observe the PC board layout guidelines to ensure
that noise and DC errors do not corrupt the current sense
signal at PHASEx and GND. Mount or place the IC close
to the low side MOSFET.
MOSFET Gate Driver (UGATEx, LGATEx)
The high side driver is designed to drive high current, low
R
the instantaneous drive current is supplied by the flying
DS(ON)
DS(ON)
is a registered trademark of Richtek Technology Corporation.
N-MOSFET(s). When configured as a floating driver
with temperature.
I
0
L
Figure 4. Valley Current Limit
LIMx
)
DS(ON)
RT8206L/M
from the MOSFET
I
I
I
L, peak
Load
LIM
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