ADP3810AR-12.6 Просмотр технического описания (PDF) - Analog Devices

Номер в каталоге

Компоненты Описание

производитель

ADP3810AR-12.6

Secondary Side, Off-Line Battery Charger Controllers

Analog Devices 

ADP3810/ADP3811

....

POWER

STAGE

CF1

1nF

R4

1.21ill

Rcs

O.2SQ

CF2

220pF

VeAT

R1

8O.61ill

R2

20kQ

r,Vc

COMP

VCTAl

1.0V

BOIill

2.0V I VSENSE

GM2

RF

CF

2.1mAN

OU-T VOLTAGE ERROR

O AMPLIFIER

3.31ill 1nF

VFe +SV

ADP381 01

ADP3811

COMP

RC1

B ~CC1

SFigure 31. Block Diagram of the Linearized Feedback Model

O amplifiers are represented by voltage controlled current sources,

the optocoupler by a current controlled current source, and the

L error amplifier by a voltage controlled voltage source.

E Design Criteria

T Charging a 6 cell NiCad battery.

E = = Max Battery Stack Voltage: VOMAX 6 x 1.67 V 10 V

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

Max Charge Current:

IoMAx=1 A

op amp is assumed to have sufficient open-loop gain and band-

Rs Fixed Value:

Pick a value for Rl:

== Rs 20 kQ

Rl 80.6 ill

width compared to the system bandwidth; as a result, it can be

considered an ideal transimpedance amplifier. The pole created

Calculated Current Sense

by the 1 nF capacitor in parallel with RF is high enough in fre-

Resistor:

= Res 0.25 Q

quency to not affect the compensation.

Calculated Voltage Sense

Divider:

Output Filter Cap:

2nd Filter Cap:

= R2 20 kQ

= = CFl 1 mF (ESR 0.1 Q)

= = ~ CF2 200 (ESR 0.2 Q)

The power stage gain equation is linearized based on primary

side current mode control with the flyback transformer operat-

ing with discontinuous inductor current. MOMAXis the maxi-

mum change in output current, which is equal to IoMAX-IoMIN'

Gain of Each Block

ADP3810/ADP381 I

Ves Input:

ADP3810/ADP3811

VSENSEInput:

ADP3810/ADP3811

Output Buffer:

Optocoupler:

Voltage Error Amplifier:

= GMI 8.3 mA/V

GM2 =2.1 mAN

= GM3 6mA/V

ITXoc = 0.36 mA/mA

AV2= !:NeNx = 0.333

Since the minimum current is 0.0 A, MoMAX= IoMAX= 1 A. The

maximum change in control voltage is set by internal circuitry

= within the 3845 to !:N e 1 V. The load resistor, RLOAD' is dif-

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

voltage limit has not been reached, so the maximum output

voltage is equal to the maximum output current times the load

resistor. Thus, the entire expression under the square root re-

duces to 1.0. Substituting these values into the general equation

Power Stage (General):

=(~ )I GM4

MOMAX

VOMAX

VIoMAx XRWAD

for the power stage yields the specific gain values shown for

GM4.

Power Stage

(Voltage Loop):

Power Stage

(Current Loop):

= GM4 0.091 AN

= GM4 1.0 AN

When calculating the loop gain for the voltage loop and the cur-

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

The gains for the ADP3810/ADP381 I GM amplifiers are based consider. For the current loop, the battery is present and un-

on typical measurements of the IC's open-loop gain, and they

charged. Thus, the battery is modeled as a very large capaci-

are expressed in units of milliamps per volt. The dc voltage gain tance (greater than 1 Farad). For the voltage loop, the battery is

REV. 0

-13-

Share Link: