Rainbow Electronics MAX15010 - Manual (Page 17)

Setting the Overvoltage Threshold
(MAX15008 Only)
The MAX15008 provides an accurate means to set the
overvoltage threshold for the OVP controller using
FB_PROT. Use a resistive voltage-divider to set the
desired overvoltage threshold (Figure 5). FB_PROT has
a rising 1.235V threshold with a 4% falling hysteresis.
Begin by selecting the total end-to-end resistance,
R
TOTAL = R 5 + R 6 . Choose R TOTAL to yield a total cur-
rent equivalent to a minimum of 100 x I FB_PROT
(FB_PROT’s input maximum bias current) at the
desired overvoltage threshold. See the
Electrical
Characteristics table.
For example:
With an overvoltage threshold (V
OV
) set to 20V,
R TOTAL < 20V / (100 x I FB_PROT ), where I FB_PROT is
FB_PROT’s maximum 100nA bias current:
R
TOTAL
< 2MΩ
Use the following formula to calculate R 6 :
R
6
= V
TH_PROT
x R
TOTAL
/ V
OV
where V TH_PROT is the 1.235V FB_PROT rising thresh-
old and V OV is the desired overvoltage threshold. R 6 =
124kΩ:
R TOTAL = R 5 + R 6
where R
5
= 1.88MΩ. Use a standard 1.87MΩ resistor.
A lower value for total resistance dissipates more
power, but provides better accuracy and robustness
against external disturbances.
Input Transients Clamping
When the external MOSFET is turned off during an
overvoltage event, stray inductance in the power path
may cause additional input-voltage spikes that exceed
the V
DSS rating of the external MOSFET or the absolute
maximum rating for the MAX15008 (IN, TRACK).
Minimize stray inductance in the power path using wide
traces and minimize the loop area included by the
power traces and the return ground path.
For further protection, add a zener diode or transient
voltage suppressor (TVS) rated below the absolute
maximum rating limits (Figure 6).
MAX15008/MAX15010
Automotive 300mA LDO Voltage Regulators
with Tracker Output and Overvoltage Protector
______________________________________________________________________________________ 17
R6
R5
R5
R6
IN V IN
FB_PROT
SGND
GATE
SOURCE
PROTECTOR
OUTPUT
MAX15008
IN V IN
FB_PROT
SGND
GATE
SOURCE
PROTECTOR
OUTPUT
MAX15008
Figure 5. Setting the Overvoltage Threshold (MAX15008)
IN
V IN
SGND
GATE
SOURCE
TVS
MAX15008
LOAD
Figure 6. Protecting the MAX15008 Input from High-Voltage
Transients