RT8206L RICHTEK [Richtek Technology Corporation], RT8206L Datasheet - Page 23

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

internal circuitry will be shut down during thermal shutdown.
The RT8206L/M may trigger thermal shutdown if the LDO
is not supplied from VOUTx, while input voltage on VIN
and drawing current from the LDO are too high. Even if
the LDO is supplied from VOUTx, overloading the LDO
causes large power dissipation on automatic switches,
which may result in thermal shutdown.
Discharge Mode
When standby or shutdown mode occurs, or the output
under voltage fault latch is set, the output discharge mode
is triggered. During discharge mode, the output capacitor
will be discharged to GND through an internal 20Ω switch.
Shutdown Mode
The RT8206L/M SMPS1, SMPS2 and LDO have
independent enabling control. Drive ENLDO, EN1 and EN2
below the precise input falling edge trip level to place the
RT8206L/M in its low power shutdown state. The
RT8206L/M consumes only 20μA of quiescent current
while in shutdown. When shutdown mode is activated,
the reference turns off. The accurate 1V falling-edge
threshold on the ENLDO can be used to detect a specific
analog voltage level and shutdown the device. Once in
shutdown, the 1.6V rising edge threshold activates,
providing sufficient hysteresis for most application.
Power Up Sequencing and On/Off Controls (ENx)
EN1 and EN2 control SMPS power-up sequencing. When
the RT8206L/M applies in the single channel mode, EN1
or EN2 enables the respective outputs when ENx voltage
rises above 2.5V, and disables the respective outputs when
ENx voltage falls below 1.8V.
Connecting one ENx to VCC and the other to REF will
force the latter one's output to start only after the former
one regulates.
If both ENx are connected to REF, each output will wait
for the regulation of the other one. However, in this situation,
neither of the two ENx will be in regulation.
Copyright
DS8206L/M-07 June 2012
©
2012 Richtek Technology Corporation. All rights reserved.
Output Voltage Setting (FBx)
Connect FB1 directly to GND or VCC for a fixed 5V output
(VOUT1). Connect FB2 directly to GND or VCC for a fixed
3.3V output (VOUT2).
The output voltage can also be adjusted from 2V to 5.5V
with a resistor-divider network (Figure 6). The following
equation is for adjusting the output voltage. Choose R2 to
be approximately 10kΩ, and solve for R1 using the following
equation :
where V
Output Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or L
where LIR is the ratio of the peak-to-peak ripple current to
the average inductor current.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite cores
are often the best choice, because the powdered iron is
inexpensive and can work well at 200kHz. The core must
be large enough to prevent it from saturating at the peak
inductor current (I
This inductor ripple current also impacts transient-response
performance, especially at low V
Low inductor values allow the inductor current to slew
faster, replenishing charge removed from the output filter
L =
V
I
PEAK
OUTx
Figure 6. Setting VOUTx with a Resistor-Divider
is a registered trademark of Richtek Technology Corporation.
t
ON
L
= I
IR
= V
FBx
LOAD(MAX)
×
×
IR
(V
FBx
I
UGATEx
PHASEx
LGATEx
LOAD(MAX)
) determine the inductor value as follows :
is 2V (typ.).
VOUTx
IN
GND
FBx
- V
×
⎡
⎢
⎣
PEAK
OUT
+ [(L
1
+ ⎜
⎛
⎝
) :
)
R2
R1
IR
/ 2) x I
⎞
⎟
⎠
⎤
⎥
⎦
V
IN
LOAD(MAX)
RT8206L/M
IN
− V
OUTx
]
R1
R2
www.richtek.com
V
OUTx
differences.
23