ADP3810 Analog Devices, ADP3810 Datasheet - Page 11

• Manufacturer Part Number: ADP3810
• Description: Secondary Side/ Off-Line Battery Charger Controllers
• Manufacturer: Analog Devices

Figure 27. Output Voltage Transient Response to Battery
Connect/Disconnect
NONISOLATED TOPOLOGIES
Buck Switching Regulators
The ADP3810/ADP3811 and the ADP1148 can be combined
to create a high efficiency buck regulator battery charger as
shown in Figure 28. The ADP1148 is a high efficiency, synchro-
nous, step-down regulator that controls two external MOSFETs
as shown. Similar to the previous flyback circuit, the ADP3810
controls the average charge current and the final battery voltage,
and the ADP1148 controls the cycle by cycle current. The fol-
lowing discussion explains the functionality of the circuit but
does not go into detail on the ADP1148. For more information,
the ADP1148 data sheet details the operation of the device and
gives formulas for choosing the external components.
The resistor R
which is far enough above the 1 A average current of the
ADP3810 loop to avoid interfering but still provides a safe
maximum current to protect the external components. The
ADP3810 uses a 0.25
rent. As before, a 20 k resistor is needed between R
V
performs the dual function of filtering and compensation.
The voltage loop directly senses the battery voltage. Since the
ADP3810 is used in this circuit instead of the ADP3811, V
is connected directly to the battery. The internal resistors set the
battery voltage to 8.4 V in this case. Of course, other voltage
REV. 0
CS
REF & CTRL
(0V TO 1V)
input of the ADP3810. The RC network from V
V
+V
V
CTRL
RTN
RTN
V
REF
IN
** KRL SL-1-C1-0R068J
IN
* COILTRONICS CTX-68-4
10V
0V
6V
SENSE
100
0%
90
0.1µF
10
0.1µF
sets the cycle by cycle current limit to 1.5 A,
2V/DIV
resistor, R
T
V
V
V
V
V
A
CTRL
IN
SENSE
REF
CTRL
GND
= +25 C
= 220V
= 1V
ADP3810
AC
V
CC
0.1µF
CS
COMP
, to sense the battery cur-
OUT
V
R
2k
C
1µF
50msec/DIV
CS
C1
C1
Figure 28. High Efficiency Buck Battery Charger
R
560
C
220nF
C2
C2
CS
CS
to ground
20k
>1.5V = SHUTDOWN
and the
0V = NORMAL
SENSE
1µF
68pF
–11–
C
T
options could be used, or the ADP3811 could be substituted
with external resistors for a user set voltage. Notice the two
grounds in the circuit. One ground is for the high current re-
turn to the V
circuitry. R
keep them separate as shown.
The adjustable version of the ADP1148 is used in this circuit in-
stead of a fixed output version. The output voltage is fed back
into the V
Doing so provides a secondary, higher voltage limit without
interfering with normal circuit operation. The control output of
the ADP3810 is connected through a 560
SENSE+ input of the ADP1148. The current, I
dc level on the SENSE+ pin, which is added to the current
ramp across R
SENSE+ and reduces the duty cycle of the 1148, giving nega-
tive feedback.
The circuit as shown can quickly and safely charge LiIon batter-
ies while maintaining high efficiency. The efficiency of the
ADP1148 is only degraded slightly by the addition of the
ADP3810 and external circuitry. The 1.5 mA of supply current
lowers the overall efficiency by approximately 1%–2% for maxi-
mum output current. The 0.25
the efficiency due to the I
rents. See the efficiency discussion in the ADP1148 data sheet
for more information.
Linear Regulator
A third charging circuit is shown in Figure 29. In this case, the
switching supply is replaced with a linear regulator. The ADP3811
drives the gate of an N-channel MOSFET using an external
2N3904. As before, the ADP3811 senses the charge current
through a 0.25
limit, the internal GM amplifier causes the output to go high.
This puts more voltage across R8, increasing the current in Q1.
As the current increases, the gate of M1 is pulled lower, reduc-
ing the gate to source voltage and decreasing the charge current
to complete the feedback loop. Because the ADP3811 has a
current output, an external 1 k resistor is needed from the
OUT pin to ground in order to convert the current to a voltage.
SHUTDOWN
C
S GND
T
ADP1148
V
FB
IN
P DRIVE
N DRIVE
SENSE–
CS
SENSE+
P GND
pin, which is set to regulate at V
IN
SENSE
separates the two grounds, and it is important to
V
source and the other ground for the ADP3810
75k
FB
resistor. When the current increases above the
. Higher I
10
k
P CH
IRF7204
N CH
IRF7403
2
1000pF
R
ADP3810/ADP3811
OUT
CS
560
power loss at high output cur-
increases the voltage on
sense resistor further lowers
D1
10BQ040
62µH
100
100
L*
0.25
C
100µF
R
IN
CS
R
BAT MAX
resistor to the
SENSE
50 m
220µF
C
OUT
OUT
**
V
, adjusts the
BAT
+ 0.5 V.
BATTERY