Datasheet

V
INMAX
= R1 x
OVP
TH
R3
+ UVLO
BIAS
+ R2 x + OVP
TH
OVP
TH
R3
V
INMIN
=
UVLO
TH
R2 + R3
+ UVLO
BIAS
x R1 + UVLO
TH
R2 =
R3 x V
INMAX
OVP
TH
UVLO
BIAS
x R1 x R3
OVP
TH
- R3 - R1 -
R3 =
UVLO
TH
x R1
V
INMIN
- UVLO
TH
- (UVLO
BIAS
x R1)
+ R1
V
INMAX
OVP
TH
UVLO
BIAS
x R1
OVP
TH
-
OVP
VIN
LM5060
R1
OVP
TH
2.00V
UVLO
UVLO
TH
1.60V
UVLO
BIAS
5.5 PA
V
IN
R2
R3
LM5060
SNVS628F –OCTOBER 2009–REVISED APRIL 2013 www.ti.com
Figure 29. UVLO and OVP Thresholds Set By R1, R2 and R3
The procedure to calculate the resistor values is as follows:
1. Select R1 based on current consumption allowed in the resistor divider, including UVLO
BIAS
, and
consideration of noise sensitivity. A value less than 100 kΩ is recommended, with lower values providing
improved immunity to variations in ULVO
BIAS
.
2. Calculate R3 with the following formula:
(9)
3. Calculate R2 with the following formula:
(10)
V
INMIN
is the minimum and V
INMAX
is the maximum input voltage of the design specification. All other variables
can be found in the Electrical Characteristics table of this document. To calculate the UVLO lower threshold
including its hysteresis for falling V
IN
, use (UVLO
TH
-UVLO
HYS
) instead of UVLO
TH
in the formulas above. To
calculate the OVP lower threshold including hysteresis for falling V
IN
, use (OVP
TH
-OVP
HYS
) instead of OVP
TH
.
With three given resistors R1, R2, and R3, the thresholds can be calculated with the formulas below:
(11)
Also in these two formulas, the respective lower threshold value including the hysteresis is calculated by using
(UVLO
TH
-UVLO
HYS
) instead of UVLO
TH
, and (OVP
TH
-OVP
HYS
) instead of OVP
TH
. The worst case thresholds,
over the operating temperature range, can be calculated using the respective min and max values in bold font in
the Electrical Characteristics .
Option B: UVLO and OVP can be independently adjusted using two resistor dividers as shown in Figure 30.
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