LTC3788-1 Linear Technology, LTC3788-1 Datasheet - Page 19

• Manufacturer Part Number: LTC3788-1
• Description: Dual Output Synchronous Boost Controller
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
INTV
The LTC3788-1 features two separate internal P-channel
low dropout linear regulators (LDO) that supply power at
the INTV
EXTV
pin. INTV
LTC3788-1’s internal circuitry. The VBIAS LDO and the
EXTV
supply a peak current of 50mA and must be bypassed to
ground with a minimum of 4.7μF ceramic capacitor. Good
bypassing is needed to supply the high transient currents
required by the MOSFET gate drivers and to prevent in-
teraction between the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3788-1 to be
exceeded. The INTV
gate charge current, may be supplied by either the VBIAS
LDO or the EXTV
pin is less than 4.8V, the VBIAS LDO is enabled. In this
case, power dissipation for the IC is highest and is equal
to V
on operating frequency, as discussed in the Effi ciency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 3 of the
Electrical Characteristics. For example, the LTC3788-1
INTV
supply when 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 5.4V, the LDO is in dropout and the INTV
voltage is approximately equal to EXTV
is greater than 5.4V, up to an absolute maximum of 6V,
INTV
IN
T
LDO is turned off and the EXTV
J
IN
CC
CC
CC
CC
CC
CC
CC
= 70°C + (15mA)(40V)(90°C/W) = 125°C
CC
• I
Regulators
is regulated to 5.4V.
current is limited to less than 15mA from a 40V
LDO remains on as long as the voltage applied to
remains above 4.55V. The EXTV
pin depending on the connection of the EXTV
LDO regulate INTV
CC
) at maximum V
CC
INTVCC
pin from either the VBIAS supply pin or the
powers the gate drivers and much of the
. The gate charge current is dependent
CC
LDO. When the voltage on the EXTV
CC
CC
current, which is dominated by the
voltage to 5.4V, so while EXTV
IN
.
CC
to 5.4V. Each of these can
CC
CC
CC
supply:
rises above 4.7V, the
LDO is enabled. The
CC
CC
. When EXTV
LDO attempts
CC
CC
CC
CC
CC
The following list summarizes possible connections for
EXTV
Topside MOSFET Driver Supply (C
External bootstrap capacitors C
pins supply the gate drive voltages for the topside MOS-
FETs. Capacitor C
external diode D
When one of the topside MOSFETs is to be turned on, the
driver places the C
desired MOSFET. This enhances the MOSFET and turns on
the topside switch. The switch node voltage, SW, rises to
V
on, the boost voltage is above the input supply: V
V
to be 100 times that of the total input capacitance of the
topside MOSFET(s). The reverse breakdown of the external
Schottky diode must be greater than V
Fault Conditions: Overtemperature Protection
At higher temperatures, or in cases where the internal
power dissipation causes excessive self-heating on chip
(such as an INTV
shutdown circuitry will shut down the LTC3788-1. When
the junction temperature exceeds approximately 170°C,
the overtemperature circuitry disables the INTV
causing the INTV
down the entire LTC3788-1 chip. Once the junction tem-
perature drops back to approximately 155°C, the INTV
LDO turns back on. Long term overstress (T
should be avoided as it can degrade the performance or
shorten the life of the part.
IN
IN
EXTV
INTV
lator resulting in an effi ciency penalty at high input
voltages.
EXTV
nal supply is available in the 5.4V to 6V range, it may
be used to power EXTV
with the MOSFET gate drive requirements. Ensure that
EXTV
and the BOOST pin follows. With the topside MOSFET
+ V
CC
INTVCC
:
CC
CC
CC
CC
to be powered from the internal 5.4V regu-
< VBIAS.
Connected to an External Supply. If an exter-
Left Open (or Grounded). This will cause
. The value of the boost capacitor C
CC
B
CC
B
B
in the Block Diagram is charged though
from INTV
short to ground), the overtemperature
supply to collapse and effectively shut
voltage across the gate-source of the
CC
CC
providing it is compatible
B
when the SW pin is low.
connected to the BOOST
B
LTC3788-1
, D
IN(MAX)
B
)
J
.
> 125°C)
CC
B
BOOST
19
needs
LDO,
37881f
CC
=