MAX445 Maxim, MAX445 Datasheet - Page 4

• Manufacturer Part Number: MAX445
• Description: Low-Cost / High-Resolution / 200MHz Video CRT Driver
• Manufacturer: Maxim

VIN+ and VIN- are differential video input pins designed
to allow DC coupling of a 0V to +1V signal into VIN+, with
respect to VIN-. For correct operation, it is recommend-
ed that the signals applied to these inputs be kept within
±1V, with respect to ground. Although large signals and
offsets can be handled safely without damage, exceed-
ing these limits may cause output linearity to suffer.
The contrast control is the overall DC-gain control that
will vary the voltage gain from 0V/V to -90V/V (with a
200Ω load resistor). An internal reference supply pin,
VREF, provides the nominal 5.5V needed to drive the
contrast input. Normally, a 5kΩ potentiometer between
VREF and ground is used to vary the contrast, but an
external source can be used instead of VREF, with some
degradation of gain stability with temperature.
The contrast control is a linear relationship. Vary the
input from 0V to 5V to achieve a voltage-gain range of
0V/V to -90V/V. This yields the following relationship for
overall voltage gain of this device (for IOUT < 250mA):
Low-Cost, High-Resolution, 200MHz
Video CRT Driver
Figure 1. Typical Connection Diagram
4
__________Applications Information
_______________________________________________________________________________________
(-10.5V)
ANALOG
INPUT
* STACK POLE 57-0180 OR
INDIANA GENERAL F-1650-H
BLANK
V
EE
5k
5k
1N4152
50V
D1
0.1 F
0.1 F
0.1 F
25
50
1N4152
11
2
3
4
6
7
50V
D2
VREF
OFFSET
GNDA
CONTRAST
VIN-
VIN+
BLANK
5
10
+10V
V
CC
Differential Inputs
BEAD*
24*
GND
Contrast Control
0.1 F
MAX445
16
24
V
8
VCB
EE
-10.5V
V
9
EE
1N486A
100V
BEAD*
D3
17
VCB
21
V
IOUT
EEO
19
0.1 F
The MAX445’s overall gain can vary by ±20% due to
normal process variations of internal components. Also,
if multiple devices are used in a system, all devices
must track thermally (i.e., a common heatsink).
The offset control is used to set the output quiescent
current from 5mA to 110mA (typ) when the control input
is adjusted from 0V to 5V. Normally, offset is adjusted
using a 5kΩ potentiometer between VREF and ground.
When asserted (BLANK = TTL high), this input will dis-
able the video signal and allow the output to rise to the
V
VREF is a bandgap bias reference for easy adjustment
of the offset and contrast inputs. This reference has a
nominal output voltage of 5.5V ±5% that can source up
to 4mA.
V
L3
AA
AA
10pF
22 F
100V
supply independent of offset control.
D4
- V
V
AA
O
= [V
NOTES:
C
D4 (PHILIPS BAV20 OR HITACHI 1SS91) IS ARC PROTECTION DIODE.
SEE APPLICATIONS INFORMATION SECTION.
- V
L
COMBINES CRT CATHODE, AND PARASITIC C.
O
IN
CB
(V
[V
L1
CONTRAST
200
IN
10W
R
L
(Gm) + V
(+75V)
V
AA
L2
) (0.09) + V
L
S
Bandgap Reference
OFFSET
C
R
L1, L2, L3, AND CB ARE
ELEMENTS OF THE PEAKING COIL.
L
TO THE CATHODE. R
ARC PROTECTION ELEMENT.
1
2
S
W (CARBON)
IS THE TOTAL INDUCTANCE
100
Offset Control
OFFSET
R
Blank Control
(0.02)] (R
S
(0.02)] (R
C
S
L
IS A SERIES
L
)
L
)