參數(shù)資料
型號(hào)： SC804IMLTRT
廠商： Semtech Corporation
英文描述： Fully Integrated Lithium-Ion Battery Charger System with Timer
中文描述： 完全集成的鋰離子電池充電器系統(tǒng)的計(jì)時(shí)器
文件頁(yè)數(shù)： 3/21頁(yè)
文件大小： 548K
代理商： SC804IMLTRT
11
2007 Semtech Corp.
www.semtech.com
SC804
PRELIMINARY
POWER MANAGEMENT
or
The choice of R
CT1 and RCT2 is somewhat arbitrary. The
simplest approach is to pick one and compute the other.
A good choice here is R
CT1 = 115kΩ, and RCT2 = 221kΩ, as
these standard 1% tolerance values produce the closest
match to the desired voltage divider ratio. With these
resistor nominal values,
which is, nominally, only 0.2% below the target value of
0.6591×V
VCC. The CTO network will present a load of only
15μA to a 5V charging adapter. The nominal impedance
presented to the CTO pin is R
CT1 || RCT2 = 75.6kΩ. Any
impedance on the order of 100k
Ω (or less) is acceptable.
Remote Kelvin Sensing at the Battery
The BSEN pin provides the positive Kelvin sensing voltage
feedback to the CV amplier and should be connected as
close to the battery + terminal as possible. Likewise, the
RGND pin should be connected directly to the negative
terminal of the battery. This allows the designer great
exibility in PCB layout and achieves greater accuracy
by sensing the battery voltage directly at the battery
terminals. When laying out the PCB, the designer should
route the BSEN and RGND trace directly to the battery
connection terminals, rather than just to the VOUT and
GND pins on the device.
Dropout Voltage
Dropout voltage is the smallest achievable difference
voltage between VCC and VOUT under a particular
operating condition.
Dropout voltage is encountered
V
CTO = NTCCOLD
= 0.6591 × VCC =
VCC × R
CT2
R
CT1 + RCT2
R
CT1 = 1 0.6591 = 0.5172
R
CT2
0.6591
Applications Information (Cont.)
V
CTO =
VCC × R
CT2 = 0.6577 × VCC
R
CT1 + RCT2
during CC charging whenever the current limit of the
charging adapter is less than the SC804 FCI programmed
current. In this case, the adapter voltage (the SC804
input voltage) will be pulled down to the battery voltage
(the SC804 output voltage) plus the dropout voltage.
Dropout voltage is the larger of two values: (1) the I-R
component, which is the output current multiplied by the
minimum VCC-to-VOUT path resistance (which is highly
temperature dependent), and (2) a regulated minimum
difference voltage, which is output voltage dependent
but is independent of the output current. The regulated
minimum dropout voltage results from the collapse of
internal voltage references as VOUT pulls VCC down to
near, or below, V
CV, creating a reduced output regulation
voltage approximately 200mV below VCC. Thus VCC
cannot be pulled down below VOUT + 200mV. The dropout
voltage will be larger than 200mV whenever the minimum
path resistance multiplied by the output current exceeds
200mV, but it cannot be smaller than 200mV.
This greatest-of-two-limit dropout voltage behavior is
evident in the dropout voltage typical performance plot.
When operating in Adjust Mode (next section), the
regulated minimum dropout voltage depends on the
programmed VOUT regulation voltage, and dropout also
varies with the actual output voltage during CC charging.
See Figure 4 for an illustration of dropout voltage data.
Adjust Mode
The SC804 can be congured for an output voltage
other than V
CV using Adjust (ADJ) Mode. In Adjust Mode
the output voltage is determined by an external resistor
divider from VOUT to BSEN. When BSEN is connected in
this fashion, V
VOUT (during Constant Voltage (CV) charging)
will be controlled such that the voltage at the BSEN pin
(V
BSEN) is the reference voltage VBSEN-ADJ.
The output voltage can be set to any voltage desired by
an appropriate choice of divider network resistors, within
the following limits. When the SC804 is programmed for
adjust mode, V
VOUT is required to be 150mV less than VVCC,
and V
VOUT is required to be 400mV greater than VBSEN.
V
VOUT within 150mV of VBSEN guarantees normal mode
operation. This implies that, for BSEN used as a Kelvin
sense of battery voltage, the product of the fast charge
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