LTC3826 Linear Technology, LTC3826 Datasheet - Page 21

• Manufacturer Part Number: LTC3826
• Description: 2-Phase Synchronous Step-Down Controller
• Manufacturer: Linear Technology

www.datasheet4u.com
APPLICATIONS INFORMATION
gate charge current, may be supplied by either the 5.25V
V
the EXTV
Power dissipation for the IC in this case is highest and is
equal to V
dent on operating frequency as discussed in the Effi ciency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 2 of the
Electrical Characteristics. For example, the LTC3826 INTV
current is limited to less than 24mA from a 24V supply when
in the G package and not using the EXTV
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked while
operating in continuous conduction mode (PLLIN/MODE
= INTV
When the voltage applied to EXTV
V
EXTV
EXTV
to regulate the INTV
is less than 7.5V, the LDO is in dropout and the INTV
voltage is approximately equal to EXTV
is greater than 7.5V up to an absolute maximum of 10V,
INTV
Using the EXTV
control power to be derived from one of the LTC3826’s
switching regulator outputs (4.7V ≤ V
normal operation and from the V
is out of regulation (e.g., startup, short-circuit). If more
current is required through the EXTV
ifi ed, an external Schottky diode can be added between the
EXTV
the EXTV
Signifi cant effi ciency and thermal gains can be realized
by powering INTV
rent resulting from the driver and control currents will be
scaled by a factor of (Duty Cycle)/(Switcher Effi ciency). For
5V to 10V regulator outputs, this means connecting the
EXTV
IN
IN
T
LDO is turned off and the EXTV
LDO or the 7.5V EXTV
J
CC
CC
CC
CC
CC
= 70°C + (24mA)(24V)(95°C/W) = 125°C
CC
is regulated to 7.5V.
LDO remains on as long as the voltage applied to
and INTV
pin directly to V
remains above 4.5V. The EXTV
CC
) at maximum V
CC
IN
pin is less than 4.7V, the V
pin and make sure than EXTV
• INTV
CC
CC
CC
CC
LDO allows the MOSFET driver and
pins. Do not apply more than 10V to
CC
from the output, since the V
. The gate charge current is depen-
voltage to 7.5V, so while EXTV
OUT
IN
CC
. Tying the EXTV
.
LDO. When the voltage on
IN
CC
CC
LDO when the output
rises above 4.7V, the
CC
LDO is enabled. The
IN
OUT
CC
LDO than is spec-
CC
CC
LDO is enabled.
. When EXTV
CC
≤ 10V) during
LDO attempts
CC
supply:
≤ V
pin to a 5V
IN
.
IN
cur-
CC
CC
CC
CC
supply reduces the junction temperature in the previous
example from 125°C to:
However, for 3.3V and other low voltage outputs, addi-
tional circuitry is required to derive INTV
the output.
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
2. EXTV
3. EXTV
4. EXTVCC Connected to an Output-Derived Boost Network.
T
INTV
resulting in an effi ciency penalty of up to 10% at high
input voltages.
connection for a 5V to 10V regulator and provides the
highest effi ciency.
supply is available in the 5V to 10V range, it may be
used to power EXTV
the MOSFET gate drive requirements.
For 3.3V and other low voltage regulators, effi ciency
gains can still be realized by connecting EXTV
output-derived voltage that has been boosted to greater
than 4.7V. This can be done with the capacitive charge
pump shown in Figure 8.
J
EXTV
= 70°C + (24mA)(5V)(95°C/W) = 81°C
CC
CC
CC
CC
CC
LTC3826
Figure 8. Capacitive Charge Pump for EXTV
to be powered from the internal 5.25V regulator
Connected directly to V
Connected to an External supply. If an external
Left Open (or Grounded). This will cause
PGND
CC
BG1
TG1
V
SW
C
IN
:
IN
+
N-CH
N-CH
V
CC
IN
providing it is compatible with
BAT85
L1
OUT
VN2222LL
R
. This is the normal
SENSE
0.22μF
LTC3826
CC
power from
+
CC
3826 F08
CC
BAT85
BAT85
1μF
C
21
V
OUT
OUT
to an
3826fc