ADP3810AR-16.8 Analog Devices Inc, ADP3810AR-16.8 Datasheet - Page 11

• Manufacturer Part Number: ADP3810AR-16.8
• Manufacturer: Analog Devices Inc
• Type: Battery Chargerr

Specifications of ADP3810AR-16.8

• Output Voltage: 16.8V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 16V
• Operating Temp Range: -40C to 85C
• Package Type: SOIC N
• Mounting: Surface Mount
• Pin Count: 8
• Operating Temperature Classification: Industrial
• Lead Free Status / Rohs Status: Not Compliant

NONISOLATED TOPOLOGIES
The ADP3810/ADP3811 and the ADP1148 can be combined
The resistor RSENSE s ets the cycle by cycle current limit to 1.5 A,
ADP3810 loop to avoid interfering but still provides a safe
ADP3810 uses a 0.25 Q resistor, Res, to sense the battery cur-
Ves input of the ADP3810. The RC network from Ves to ground
Figure 27. Output Voltage Transient Response to Battery
Connect/Disconnect
Buck Switching Regulators
to create a high efficiency buck regulator battery charger as
shown in Figure 28. The ADPI148 is a high efficiency,synchro-
nous, step-down regulator that controls two external MOSFETs
as shown. Similar to the previous flyback circuit, the ADP38 10
controls the average charge current and the final battery voltage,
and the ADPI148 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
givesformulas for choosing the external components.
which is far enough above the 1 A average current of the
maximum current to protect the external components. The
rent. As before, a 20 kQ resistor is needed between Res and the
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, VSENSE
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
REF & CTRL
(OV TO 1V)
VCTRL
+V'N
VREF
RTN
RTN
V'N~
..
.
COIL TRONICS CTX-684
KRLSL.1-C1-0R068J
10V
OV
\1
0%""
00""
9!1!!!!!!!!!
10
I
!!!! !!!!!
0.1pF
!!!!!
.... TA=+25'C
.... ........ .... ........ ........ ....
2VIDIV
V'N
VCTRL
VSENSE
VREF
VCTRL
GND
=
220VAC
=
ADP3810
1V
VCC
COMP
. .... .... .... ....
OUT
Vas
2kQ
CC1
1pF
RC1
50mseclD..IV
Figure 28. High Efficiency Buck Battery Charger
II
II
560Q
RC2
CC2
220nF
20kQ
>1.5V=SHUTDOWN
OV
+
;1PF
=
NORMAL
68pF
-11-
C,
The adjustable version of the ADPI148 is used in this circuit in-
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 VINsource and the other ground for the ADP3810
circuitry. Res separates the two grounds, and it is important to
keep them separate as shown.
stead of a fixed output version. The output voltage is fed back
into the VFBpin, which is set to regulate at VBAT M AX + 0.5 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 Q resistor to the
SENSE+ input of the ADP1148. The current, loUT,adjusts the
dc level on the SENSE+ pin, which is added to the current
ramp across RsENSE. H igher lOUTincreases the voltage on
SENSE+ and reduces the duty cycle of the 1148, giving nega-
tive feedback.
The circuit as shown can quickly and safely charge Lilon 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 Q sense resistor further lowers
the efficiency due to the 12x Res power loss at high output cur-
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 Q resistor. When the current increases above the
limit, the internal GM amplifier causes the output to go high.
This puts more voltage across R8, increasing the current in Ql.
As the current increases, the gate of Ml 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 ill resistor is needed from the
OUT pin to ground in order to convert the current to a voltage.
SHUTDOWN
ADP1148
V,N
P DRIVE
N DRIVE
SENSE-
SENSE+
VFB
75kQ
1000:F
ADP3810/ADP3811
560Q ;100PF
I:
-'N.
D1
1060040
62pH
100Q
t.L C'N
L'
0.25Q
Rcs
RSENSE'
50 mQ I VBAT
220PF;
COUT'!:.
I