LTC3789 LINER [Linear Technology], LTC3789 Datasheet - Page 21

• Manufacturer Part Number: LTC3789
• Description: High Voltage High Current Controller for Battery Charging and Power Management
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
Similar to the input external PMOS, the charging external
PMOS must be able to withstand a gate to source voltage
greater than V
regulated voltage at the CSP pin, whichever is less. Consider
the expected maximum current, power dissipation and
instant-on voltage drop when selecting this PMOS. The
PMOS suggestions in Table 1 are an appropriate starting
point depending on the application.
Float Voltage, Output Voltage and Instant-On Voltage
Dependencies
The formulas for setting the float voltage, output voltage
and instant-on voltage are repeated here:
V
V
V
FLOAT
OUT
OUT(INST _ ON)
=
=
R
OFB1
R
BGATE(ON)
BFB1
R
OFB2
R
+ R
=
BFB2
+ R
R
OFB2
OFB1
BFB2
(15V maximum) or the maximum
R
OFB2
• 1.193V
NOMINAL INSTANT-ON VOLTAGE
+ R
• 1.136V
NOMINAL OUTPUT VOLTAGE
OFB2
NOMINAL FLOAT VOLTAGE
• 0.974V
Figure 8. Possible Voltage Ranges for V
V
OUT(INST_ON)
100%
75%
in Ideal Scenario
VOLTAGE RANGE
105%
100%
86%
In the typical application, V
to ensure that the battery is charged fully to its intended
float voltage. On the other hand, V
programmed too high since V
voltage on CSP , depends on the same resistors R
R
output voltage regulation level is always 122.5% of the
instant-on voltage. The higher the programmed value of
V
charger PMOS is driven in the linear region where it is
less efficient.
If R
respectively, then the output voltage is set at 105% of
the float voltage and the instant-on voltage is set at 86%
of the float voltage. Figure 8 shows the range of possible
output voltages that can be set for V
with respect to V
charged in an ideal scenario.
Taking into account possible mismatches between the
resistor dividers as well as mismatches in the various
regulation loops, V
be less than 105% of V
can be fully charged. This automatically means that the
instant-on voltage level should not be programmed to be
less than 86% of V
POSSIBLE
OUT(INST_ON)
OFB2
OUTPUT
100%
OFB1
that set V
and R
POSSIBLE
INSTANT-ON
VOLTAGE RANGE
81.6%
4000 F08
OUT
, the larger the operating region when the
MINIMUM PRACTICAL
OUTPUT VOLTAGE
MINIMUM PRACTICAL
INSTANT-ON VOLTAGE
OFB2
OUT
and
FLOAT
are set to be equal to R
FLOAT
. As noted before, this means that the
OUT
to ensure the battery can be fully
FLOAT
.
should not be programmed to
OUT
OUT(INST_ON)
to ensure that the battery
is set higher than V
OUT(INST_ON)
OUT
LTC4000
should not be
BFB1
, the minimum
and R
and V
OFB1
21
FLOAT
BFB2
and
OUT
4000f