参数资料
型号: LT3651EUHE-4.2#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: BATTERY CHARGE CONTROLLER, 1100 kHz SWITCHING FREQ-MAX, PQCC36
封装: 5 X 6 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, QFN-36
文件页数: 7/22页
文件大小: 213K
代理商: LT3651EUHE-4.2#PBF
LT3651-4.1/LT3651-4.2
15
365142fb
Note the LT3651 internally integrates the input limit
signals. This should normally provide sufficient filtering
and reduce the sensitivity to current spikes. For the best
accuracy take care in provide good Kelvin connections
from RCL to CLP, CLN.
Further flexibility is possible by dynamically altering the
ILIM pin. Different resistor values could be switched in
to create unique input limit conditions. The ILIM pin can
also be tied to a servo amplifier for other options. See the
information in the following section concerning IRNG/SS
programming for examples.
RNG/SS: Dynamic Current Adjust
The RNG/SS pin gives the user the capability to adjust
maximum charge current dynamically. The part sources
50μA from the pin, so connecting a resistor to ground
develops a voltage. The voltage on the RNG/SS pin cor-
responds to ten times the maximum voltage across the
charge current sense resistor, RSENSE. The defining equa-
tions for charge current are:
IMAX(RNG/SS) =
VRNG/SS
10.8 RSENSE
=
50μA RRNG/SS
10.8 RSENSE
IMAX(RNG/SS) is the maximum charge current.
The programming range for RNG/SS is 0V to 1V. Voltages
higher than 1V have no effect on the maximum charge
current. The default maximum sense voltage is 95mV
and is obtained if RRNG/SS is greater than 20k or if the
pin is left open.
For example, say you want to reduce the maximum charge
current to 50% of the maximum value. Set RNG/SS to 0.5V
(50% of 1V), imposing a 46mV maximum sense voltage.
Per the above equation, 0.5V on RNG/SS requires a 10k
resistor. If the charge current needs to be dynamically
adjustable then Figure 5 shows one method.
Active servos can also be used to impose voltages on the
RNG/SS pin, provided they can only sink current. Active
circuits that source current cannot be used to drive the
RNG/SS pin. An example is shown in Figure 6.
RNG/SS: Soft-Start
Soft-start functionality is also supported by the RNG/SS
pin. The 50μA sourced from the RNG/SS pin can linearly
charge a capacitor, CRNG/SS, connected from the RNG/SS
pin to ground (see Figure 7). The maximum charge current
follows this voltage. Thus, the charge current increases
from zero to the fully programmed value as the capacitor
charges from 0V to 1V. The value of CRNG/SS is calculated
based on the desired time to full current (tSS) following
the relation:
CRNG/SS = 50μA tSS
The RNG/SS pin is pulled to ground internally when charg-
ing is terminated so each new charging cycle begins with
a soft-start cycle. RNG/SS is also pulled to ground during
bad battery and NTC fault conditions, so a graceful recovery
from these faults is possible.
APPLICATIONS INFORMATION
LT3651
RNG/SS
10k
365142 F05
LOGIC HIGH = HALF CURRENT
Figure 5. Using the RNG/SS Pin for
Digital Control of Maximum Charge Current
LT3651
RNG/SS
SERVO
REFERENCE
365142 F06
+
Figure 6. Driving the RNG/SS Pin
with a Current-Sink Active Servo Amplifier
LT3651
RNG/SS
CRNG/SS
365142 F07
Figure 7. Using the RNG/SS Pin for Soft-Start
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