LT1620 Linear Technology, LT1620 Datasheet - Page 6

• Manufacturer Part Number: LT1620
• Description: Rail-to-Rail Current Sense Amplifier
• Manufacturer: Linear Technology

LT1620/LT1621
APPLICATIONS
Charge Current Programming
Output current delivered during current mode operation is
determined through programming the voltage at the PROG
pin (V
is obtained with (V
biased with a precision 5V supply produced by the LTC1435,
enabling use of a simple resistor divider from V
ground for a V
Thevenin impedance at the PROG pin, values of R
and R
should be decoupled to the V
Different values of charging current can be obtained by
changing the values of the resistors in the V
divider to raise or lower the value of the programming
voltage, or by changing the sense resistor to an appropri-
ate value as described above.
6
R
15.75k
1%
P2
R
1%
PROG
3k
P2
P1
= 15.75k are readily calculated. The PROG pin
C18
0.1 F
). As mentioned above, optimum performance
C16
0.1 F
PROG
0.1 F
C15
U
CC
5
6
7
8
reference. Using the desired 2.5k
IN
V
PROG
AVG
CC
– V
+
LT1620MS8
C17, 0.01 F
INFORMATION
U
PROG
C14
1nF
RUN
CC
SENSE
GND
I
OUT
IN
) = 0.8V. The LT1620 is
R1
1k
supply.
–
0.033 F
X7R
C13
4
3
2
1
W
Figure 2. LT1620/LTC1435 Battery Charger
R2
1.5M
C12, 0.1 F
C9, 100pF
PROG
100pF
U
C10
C11, 56pF
P1
setting
CC
= 3k
R
110k
0.1%
to
F2
C
RUN/SS
I
SFB
SGND
V
SENSE
SENSE
TH
OSC
OSENSE
LTC1435
–
+
1.44M
0.1%
C8, 100pF
Output Float Voltage
The 3.2A charger circuit is designed for a 4-cell Li-Ion
battery, or a battery float voltage of 16.8V. This voltage is
programmed through a resistor divider feedback to the
LTC1435 V
voltage. Resistor values are determined through the rela-
tion: R
yields R
Other Decoupling Concerns
The application schematic shown in Figure 2 employs
several additional decoupling capacitors. Due to the inher-
ently noisy environment created in switching applications,
decoupling of sensitive nodes is prudent. As noted in the
schematic, decoupling capacitors are included on the
current programming pin (PROG) to the V
R
F1
EXTV
INTV
BOOST
PGND
SW
V
TG
BG
CC
CC
IN
F1
F1
= (V
= 1.44M.
OSENSE
BATT
* D1, D2: CENTRAL
D2*
SEMICONDUCTOR CMDSH-3
C4
0.1 F
+
C5, 0.1 F
– 1.19)/(1.19/R
C7
4.7 F
D1*
pin, referencing its 1.19V bandgap
0.1 F
C6
Si4412DY
Si4412DY
27 H
+
L1
F2
C1
22 F
35V
). Setting R
R
0.025
LT1620/21 • F02
SENSE
+
C2
22 F
35V
+
CC
C3
22 F
35V
F2
V
17.3V TO 28V
rail and
IN
= 110k
V
16.8V
BATT
Li-ION