THS3122 Datasheet, PDF (15/43 Pages) Texas Instruments – LOW-NOISE, HIGH-SPEED, 450 mA CURRENT FEEDBACK AMPLIFIERS

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THS3122, THS3125
SLOS382E – SEPTEMBER 2001 – REVISED MAY 2015
Feature Description (continued)
8.2.3 Power-Down Reference Pin Operation
In addition to the shutdown pin, the THS3125 features a reference pin (REF) which allows the user to control the
enable or disable power-down voltage levels applied to the SHUTDOWN pin. In most split-supply applications,
the reference pin is connected to ground. In either case, the user must be aware of voltage-level thresholds that
apply to the shutdown pin. Table 1 shows examples and illustrate the relationship between the reference voltage
and the power-down thresholds. In the table, the threshold levels are derived by the following equations:
SHUTDOWN ≤ REF + 0.8 V for enable
SHUTDOWN ≥ REF + 2V for disable
Where the usable range at the REF pin is:
V_CC– ≤ V_REF ≤ (V_CC+ – 4V)
The recommended mode of operation is to tie the REF pin to midrail, therefore setting the enable/disable
thresholds to V_(midrail) + 0.8 V and V_(midrail) = 2 V, respectively.
SUPPLY VOLTAGE (V)
±15, ±5
±15
±15
±5
±5
+30
+10
Table 1. Shutdown Threshold Voltage Levels
REFERENCE PIN VOLTAGE (V)
0
2.0
–2.0
1.0
–1.0
15.0
5.0
ENABLE LEVEL (V)
0.8
2.8
–1.2
1.8
–0.2
15.8
5.8
DISABLE LEVEL (V)
2.0
4.0
0
3.0
1.0
17
7.0
Note that if the REF pin is left unterminated, it floats to the positive rail and falls outside of the recommended
operating range given above V_CC– ≤ V_REF ≤ (V_CC+ – 4V). As a result, it no longer serves as a reliable reference
for the SHUTDOWN pin, and the enable/disable thresholds given above no longer apply. If the SHUTDOWN pin
is also left unterminated, it floats to the positive rail and the device is disabled. If balanced, split supplies are
used (±V_S) and the REF and SHUTDOWN pins are grounded, the device is enabled.
Copyright © 2001–2015, Texas Instruments Incorporated
Product Folder Links: THS3122 THS3125
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