2252-DEMO THAT Corporation, 2252-DEMO Datasheet - Page 5

• Manufacturer Part Number: 2252-DEMO
• Description: Power Management Modules & Development Tools RMS Detector Demo Board
• Manufacturer: THAT Corporation
• Type: AC/DC Switching Convertersr

Specifications of 2252-DEMO

• Input Voltage: 12 V
• Maximum Operating Temperature: + 75 C
• Minimum Operating Temperature: - 20 C
• Product: Power Management Modules
• Supply Current: 1 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

600032 Rev 02
given in put fre quency, f
duce rip ple at the ex pense of lon ger at tack and re -
lease times. For f
out put is given by: V
rms rip ple volt age.
Taking the Square Root
The square root por tion of the Root-Mean Square
is im plied by the con stant of pro por tion al ity for
the out put volt age: it is not com puted ex plic itly.
This is be cause, in the log rep re sen ta tion, tak ing
the square root is equiv a lent to di vi sion by two.
The volt age at pin 6 is pro por tional to the mean of
the square at ap prox i mately 3 mV/dB, and pro por -
tional to the square root of the mean of the square
at ap prox i mately 6 mV/dB.
Out put Buffering and Level Shifting
The volt age at pin 6 is buf fered by OA3, and level
shifted down by the bias volt age V3. Level shift ing
is re quired so that the out put volt age will be zero
when the rms in put cur rent reaches a pre de ter -
mined value, I
Fig ure 6. 2252 DC Out put Vs. AC In put Level
Fig ure 5. Tone Burst Re sponse
in0
. This cur rent is of ten called level
in
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
>>
R
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
4 p t
»
1
in
4
, the rip ple volt age at the
p
. Larger val ues of
V
2
T
f
in
t
, where V
R
is the
re -
match, and rep re sents the 0 dB ref er ence of the
cir cuit.
The var i ous level shifts through out the 2252 are as
fol lows: V2 rep re sents one di ode drop, so the volt -
age at the emit ter of Q4 is +1V
OA2 is two di ode drops higher than this, or
+3V
out put of OA2, so the volt age at pin 6 will be
+2V
set ting the volt age at pin 7 to 0 V.
Of course, the ac tual value of all these level shifts
is de pend ent on the cur rents through the tran sis -
tors re spon si ble for each V
turn, are de pend ent on the bias pro gram ming cur -
rent in pin 2 (I
from pin 6 (I
fol lows:
I
caus ing 0 V out put, I
I
from the ge om e try of the tran sis tors in volved.
Fig ure 6 plots out put volt age ver sus in put level for
a 2252 in its rec om mended cir cuit con fig u ra tion
(Fig ure 4). In this plot, 0 dBr
plots out put volt age for sev eral dif fer ent con -
stant-amplitude fre quency sweeps for the same cir -
cuit. The ver ti cal di vi sions are 60 mV apart,
rep re sent ing ap prox i mately 10 dB in cre ments. Full
au dio band width is main tained over a 60 dB dy -
namic range.
Cur rent Pro gramming
All the in ter nal cur rent sources in the 2252 are
slaved to the cur rent in pin 2, I
above, the choice of this cur rent af fects I
is nor mally set by a re sis tor from pin 2 to ground
(V
is nor mally V
sup ply volt age.
Sym me try Ad just ment
The rec ti fier (Q1 through Q3 and OA1) de pends on
the match ing be tween Q1 and Q2 for ac cu rate re -
BIAS
in
CC
0
=
BE
BE
is the cur rent in pin 2. The fac tor 2.9 de rives
would do also). Note that the volt age at pin 2
Fig ure 7. 2252 DC Out put Vs. Fre quency at
. Q6 will sub t ract one di ode drop from the
. Finally, V3 rep re sents two di ode drops,
I
BIAS T
2 9
.
I
T
EE
,
). This de pend ence may be given as
BIAS
+ 2.1 V, where V
where I
Var i ous Levels
) and the tim ing cur rent pulled
T
is the cur rent in pin 6, and
in0
BE
is the in put cur rent
. These cur rents, in
BIAS
BE
EE
43 mV. Fig ure 7
. The out put of
. As men tioned
is the neg a tive
in0
. I
Page 5
BIAS