ISL59112IEZ-T7 View Datasheet(PDF) - Renesas Electronics
Part Name
Description
Manufacturer
ISL59112IEZ-T7 Datasheet PDF : 8 Pages
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ISL59112
VDD
IN
RIN
75
CIN
100nF
SYNC CLAMP
VDD
VDD
+
-
IN
VDC
+
-
EN
GND
EN = GND: SHUTDOWN IDD~0
EN = VDD: ACTIVE IDD~2.0mA
SAG
NETWORK
OUT
R6
R7
SAG
R5
AC COUPLING
CAPACITOR
C5
47µF
C4
22µF
R4
75
75
FIGURE 11. BLOCK DIAGRAM
Application Information
The ISL59112 is a single supply rail-to-rail output buffer
achieving a -3dB bandwidth of around 40MHz and slew rate of
about 85V/µs while demanding only 2mA of supply current.
This part is ideally suited for applications with specific
micropower consumption and high bandwidth demands. As
described in both the performance characteristics section and
the features section, the ISL59112 is designed to be very
attractive for portable composite video applications.
The ISL59112 features a sync clamp and SAG network at the
output facilitating reduction of typically large AC coupling
capacitors. See Figure 11.
Internal Sync Clamp
The typical embedded video DAC operates from a ground
referenced single supply. This becomes an issue because the
lower level of the sync pulse output may be at a 0V reference
level to some positive level. The problem is presenting a 0V
input to most single supply driven amplifiers will saturate the
output stage of the amplifier, resulting in a clipped sync tip and
degrading the video image. A larger positive reference may
offset the input above its positive range.
The ISL59112 features an internal sync clamp and an offset
function to level shift the entire video signal to the best level
before it reaches the input of the amplifier stage. These
features are also helpful to avoid saturation of the output stage
of the amplifier by setting the signal closer to the best voltage
range.
The simplified block diagram of the ISL59112 in Figure 11 is
divided into four sections. The first (Section A) is the Sync
Clamp. The AC coupled video sync signal is pulled negative by
a current source at the input of the comparator amplifier. When
the sync tip goes below the comparator threshold, the output
comparator is driven negative and the PMOS device turns on
clamping sync tip to near ground level.
AC Output Coupling and the SAG Network
Composite video signals carry viable information at
frequencies as low as 30Hz up to 5MHz. When a video system
output is AC coupled it is critical that the filter represented by
the output coupling capacitor and the surrounding resistance
network provide a band pass function with a low pass band low
enough to exclude very low frequencies down to DC, and with
a high pass band pass sufficiently high to include frequencies
at the higher end of the video spectrum.
FN6142 Rev 4.00
March 15, 2007
Page 5 of 8
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