ADP3810AR-16.8 Analog Devices Inc, ADP3810AR-16.8 Datasheet - Page 13

• 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

ADP3810/ADP381 I
ADP3810/ADP3811
ADP3810/ADP3811
Voltage Error Amplifier:
The gains for the ADP3810/ADP381 I GM amplifiers are based
the optocoupler by a current controlled current source, and the
error amplifier by a voltage controlled voltage source.
Design Criteria
Max Battery
Max Charge Current:
Rs Fixed Value:
Pick a value for Rl:
Calculated Voltage Sense
Output Filter Cap:
2nd Filter Cap:
Optocoupler:
Power Stage (General):
Power Stage
Power Stage
on typical measurements of the IC's open-loop gain, and they
are expressed in units of milliamps per volt. The dc voltage gain
amplifiers are represented by voltage controlled current sources,
Charging a 6 cell NiCad battery.
Calculated Current Sense
Gain of Each Block
REV. 0
Divider:
Ves Input:
VSENSE Input:
Output Buffer:
(Voltage Loop):
Resistor:
(Current Loop):
Stack Voltage:
VOLTAGE ERROR
AMPLIFIER
r,Vc
GM3
ITXoc = 0.36 mA/mA
AV2= !:NeNx = 0.333
GM4
GM4
GM4
VOMAX
IoMAx
Rl
Res
R2
GMI
GM2
Rs
CFl
CF2
=
=
=
=
=
=
20 kQ
=
= ~
=
=
80.6 ill
20 kQ
COMP
=
=
VFe
200
Figure 31. Block Diagram of the Linearized Feedback Model
0.25 Q
1 mF (ESR
=
=
6mA/V
0.091 AN
(
1.0 AN
8.3 mA/V
2.1 mAN
MOMAX
1 A
POWER
6 x 1.67 V
STAGE
~
3.31ill
RF
+SV
(ESR
)
=
V
CF
1nF
I
IoMAx XRWAD
=
....
0.1 Q)
=
0.2 Q)
10 V
V
OMAX
VCTAl
1.0V
OUT -
CF1
1nF
-13-
BOIill
voltage limit has not been reached, so the maximum output
voltage is equal to the maximum output current times the load
for the power stage yields the specific gain values shown for
When calculating the loop gain for the voltage loop and the cur-
of these stages is the value of GM times the load resistance. At the
COMP pin, the internal load resistance, RS, is typically400 kQ.
The optocoupler gain is the typical value taken from the
MOC8103 data sheet. The voltage error amplifier gain is due
to the resistor divider internal to the 3845 only. Vx is the out-
put of the internal amplifier, as labeled in Figure 31. The actual
op amp is assumed to have sufficient open-loop gain and band-
width compared to the system bandwidth; as a result, it can be
considered an ideal transimpedance amplifier. The pole created
by the 1 nF capacitor in parallel with RF is high enough in fre-
quency to not affect the compensation.
The power stage gain equation is linearized based on primary
side current mode control with the flyback transformer operat-
ing with discontinuous inductor current. MOMAX is the maxi-
mum change in output current, which is equal to IoMAX-IoMIN'
Since the minimum current is 0.0 A, MoMAX = IoMAX = 1 A. The
maximum change in control voltage is set by internal circuitry
within
ferent for the voltage and current loop cases. For the voltage
loop without the battery, the effective load is R4, but for the
current loop, the effective load is Res. In the current loop, the
resistor. Thus, the entire expression under the square root re-
duces to 1.0. Substituting these values into the general equation
GM4.
rent loop, there are two main differences. First, GM2 applies
only to the voltage loop, and GMI applies only to the current
loop. Use the appropriate GM input stage for the particular
loop calculations. Second, there are three battery conditions to
consider. For the current loop, the battery is present and un-
charged. Thus, the battery is modeled as a very large capaci-
tance (greater than 1 Farad). For the voltage loop, the battery is
R4
1.21ill
the 3845 to !:N e
O.2SQ
Rcs
ADP381 01
ADP3811
CF2
220pF
~CC1
=
COMP
RC1
1 V. The
VeAT
8O.61ill
20kQ
R1
R2
ADP3810/ADP3811
2.0V
I VSENSE
2.1mAN
GM2
load resistor,
RLOAD' is dif-