MAX4090 Maxim, MAX4090 Datasheet - Page 9

• Manufacturer Part Number: MAX4090
• Description: The MAX4090 3V/5V, 6dB video buffer with sync-tip clamp, and low-power shutdown mode is available in tiny SOT23 and SC70 packages
• Manufacturer: Maxim

In a 5V application, the MAX4090 can use the sag con-
figuration if an AC-coupled output video signal is
required. Sag correction refers to the low-frequency
compensation for the highpass filter formed by the
150Ω load and the output capacitor. In video applica-
tions, the cutoff frequency must be low enough to pass
the vertical sync interval to avoid field tilt. This cutoff
frequency should be less than 5Hz, and the coupling
capacitor must be very large in normal configuration,
Figure 4. 3rd-Order Butterworth LPF with MAX4090
Table 2. Bench Measurement Values
Table 4. Bench Measurement Values
R1 = R2
R1 = R2 (Ω)
150
200
300
(Ω)
75
CURRENT
VIDEO
150
300
DAC
75
(p f )
330
150
120
C1
82
150Ω
C1 (pF)
_______________________________________________________________________________________
3V/5V, 6dB Video Buffer with Sync-Tip Clamp
R1
220
120
56
(µH)
1.8
3.9
4.7
8.2
L1
3-POLE RECONSTRUCTION LPF
R
100
(Ω)
50
50
0
C1
120pF
IS
C2 (pF)
220
120
56
4.7μH
6.8pF
L1
C3
(MHz)
3dB
BW
8.7
9.0
9.3
8.7
120pF
C2
Sag Correction
A T T EN U A T I O N
C3 (pF)
AT 27MHz
15.0
6.8
3.3
(dB)
20
20
22
20
R2
150Ω
and 150nA Shutdown Current
L (µH)
10.0
2.2
4.7
49.9Ω
R
V
IS
CC
typically > 220µF. In sag configuration, the MAX4090
eliminates the need for large coupling capacitors, and
instead requires two 22µF capacitors (Figure 6) to
reach the same performance as the large capacitor.
Bench experiments show that increasing the output
coupling capacitor C5 beyond 47µF does not improve
the performance. If the supply voltage is less than 4.5V,
the sag correction is not recommended for the
MAX4090.
Table 3. 3rd-Order Butterworth Lowpass
Filter Normalized Values
Rn1 = Rn2
0.1μF
C4
(Ω)
1
R
IS
100
50
0
(Ω)
SHDN
IN
Cn1 (F)
0.923
MAX4090
GND
V
CC
3dB BW (MHz)
OUT
FB
Cn2 (F)
9.3
8.9
9.0
0.923
C7
1μF
Cn3 (F)
ATTENUATION AT
0.06
27MHz (dB)
75Ω
R3
43
50
45
V
Ln1 (H)
CC
1.846
V
OUT
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