TDA4887PS Datasheet, PDF (48/68 Pages) NXP Semiconductors – 160 MHz bus-controlled monitor video preamplifier

Philips Semiconductors
160 MHz bus-controlled monitor video
preamplifier
Product specification
TDA4887PS
12.4.3 AVOIDING NEGATIVE INPUT VOLTAGES AT BLANKING
AND CLAMPING INPUT PINS
Negative voltages on any input pin causes ESD protection
diodes and other internal junctions will become
open-circuit resulting in substrate current injection.
Substrate currents can generate parasitic effects that are
not completely predictable. Signal inputs (pins 6 and 10)
are neighbouring clamping inputs (pins 5 and 11) and can
therefore suffer from larger leakage currents during
negative clamping pulse glitches. An internal circuit in
combination with an external resistor protects the pins
from negative voltages (see Fig.25).
At pin voltages near to ground level, the voltage difference
between the internal reference voltage V_ref and the base
voltage of TR1, which is 2V_BE higher than the pin voltage,
generates a current through R1 which is amplified to the
output by transistor TR1. The voltage drop at the external
resistor R_ext stabilizes voltage V_pin near ground. The
recommended value for R_ext is 1 kΩ.
handbook, full pagewidth
clamping pulse
ground
Rext
Vi
R1
6 kΩ
Vref = 2VBE
VP
8V
TR1
TR3
TDA4887PS
TR2
Vpin
junctions from pin to substrate
MHB956
Fig.25 Protection circuit at pins CLI and HFB.
2001 Oct 19
48