LTC2914_15 Datasheet, PDF (11/18 Pages) Linear Technology – Quad UV/OV Positive/Negative Voltage Monitor

LTC2914
applications information
3. Determine R_C to complete the design.
R_C
=
–5V – 1V
9.947µA
− 46.4k − 8.45k ≈ 549k
V_CC
5V
R_A
46.4k
R_B
8.45k
R_C
549k
V_CC
REF
OV
LTC2914
VH3
UV
VL3
SEL
GND
V3
–5V ±10%
2914 F04
Figure 4. Negative Supply Monitor
2. Calculate R_CUV based on the desired undervoltage trip
point of –6V.
R_CUV = (R_AUV +R_BUV )•
V_UV
V_REF
=
(49.9k + 49.9k)•
–6V – 1V
1V
≈ 698k
3. Calculate R_AOV and I_na
R_AOV
=
V_REF – 0.5V
I_nd
=
1V – 0.5V
10µA
≈ 49.9k
I_na ≈ 10.020µA
4. Calculate R_BOV for a desired overvoltage trip point of
–30V.
Negative Voltage Monitoring Example 2
Negative voltage monitoring applications with wide operat-
ing voltage ranges such that:
2 • V_UV < V_OV
R_BOV =
0.5V – V_OV
I_na
=
0.5V – 30 –
10.020µA
1
≈
3.01M
V_CC
5V
create situations where the VH or VL pins exceeds the
–0.3V absolute maximum voltage ratings. To ensure that
the LTC2914 operates within its design specifications,
utilize the equations shown below to determine proper
resistor sizing for the circuit in Figure 5. In the following
example, the undervoltage trip point is –6V. The overvolt-
age trip point is –30V.
1A. Find R_AUV and R_BUV and let node A be a virtual ground,
which ensures that the diode current will not affect the
voltage monitor threshold accuracy. Let the resistive
divider current I_nd = 10µA.
R_AUV
=
V_REF – 0.5V
I_nd
=
1V – 0.5V
10µA
≈ 49.9k
R_AUV = R_BUV
1B. Calculate I_na using the resistor values chosen above.
I_na =
V_REF – 0.5V
R_AUV
=
1V – 0.5V
R_AUV
≈ 10.020µA
V_CC
R_AUV
49.9k
R_AOV
49.9k
R_BOV
3.01M
REF
OV
LTC2914
VH3
UV
VL3
SEL
R_BUV
D1
49.9k
GND
A
R_CUV
698k
2914 F05
V3
Figure 5. Negative Supply Monitor for Wide Operating Range
Power-Up/Power-Down
As soon as V_CC reaches 1V during power-up, the UV output
asserts low and the OV output weakly pulls to V_CC.
The LTC2914 is guaranteed to assert UV low and OV high
under conditions of low V_CC, down to V_CC = 1V. Above V_CC
= 2V (2.1V maximum) the VH and VL inputs take control.
Once all VH inputs and V_CC become valid an internal timer
is started. After an adjustable delay time, UV weakly pulls
high.
2914fc
For more information www.linear.com/LTC2914
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