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MAX15010ATJ+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24
MAX15008/MAX15010
Setting the
RESET
Timeout Period
The reset timeout period is adjustable to accommodate
a variety of applications. Set the reset timeout period by
connecting a capacitor, C
RESET
, between CT and
SGND. Use the following formula to select the reset
timeout period, t
RESET
:
t
RESET
= C
RESET
x V
CT_TH
/ I
CT
where t
RESET
is in seconds and C
RESET
is in µF.
V
CT_TH
is the CT ramp threshold in volts and I
CT
is the
CT ramp current in µA, as described in the
Electrical
Characteristics
table.
Leave CT open to select an internally fixed timeout peri-
od of 10µs. To maintain reset timeout accuracy, use a
low-leakage (< 10nA) type capacitor.
Tracker Input/Feedback Adjustment
The tracker can be powered from the LDO input supply
voltage or an independent voltage source. It is
designed to supply power to a remote sensor and its
supply input, TRACK, is able to handle the severe con-
ditions in automotive applications such as battery
reversal and load-dump transients up to 45V.
The tracker feedback, FB_TRK, and a separate tracker
reference voltage input, ADJ, offer the flexibility of set-
ting the tracker output to be lower, equal to, or higher
than the main (LDO) output. Other external voltages
can also be tracked.
Connect ADJ to OUT_LDO and FB_TRK to OUT_TRK to
track the LDO output voltage directly (Figure 4a). To
track a voltage higher than V
OUT_LDO
, directly connect
ADJ to OUT_LDO and connect FB_TRK to OUT_TRK
through a resistive voltage-divider (Figure 4b). To track
a voltage lower than the LDO regulator output,
V
OUT_LDO
, directly connect FB_TRK to OUT_TRK and
connect ADJ to OUT_LDO through a resistive voltage-
divider (Figure 4c). To track an external voltage V
X
with
a generic attenuation/amplification ratio, connect resis-
tive voltage-dividers between ADJ and the voltage input
or output to be tracked (V
X
), and between OUT_TRK
and FB_TRK (Figure 4d). Pay attention to the resistive
loading of the voltage V
X
due to the divider R5, R6.
To track the internal REF voltage (1.235V), directly connect
ADJ to REF. The voltage at FB_TRK or ADJ should be
greater than or equal to 1.1V and less than V
TRACK
- 0.5V.
Resistors should have a tolerance of 1% or better. Their
values should be low enough to ensure that the divider
current is at least 100x the maximum input bias current
at pins FB_TRK and ADJ (I
FB_TRK_ADJ
, max = 0.2µA).
Automotive 300mA LDO Voltage Regulators
with Tracker Output and Overvoltage Protector
16 ______________________________________________________________________________________
IN
LDO
OUTPUT
V
IN
OUT_TRK
OUT_LDO
TRACKER
OUTPUT
FB_TRK
ADJ
MAX15008
MAX15010
TRACK
IN
LDO
OUTPUT
R3
V
IN
OUT_TRK
OUT_LDO
TRACKER
OUTPUT
ADJ
MAX15008
MAX15010
R4
FB_TRK
R5
R6
R6
TRACK
TO TRACK V
OUT_LDO
:
V
OUT_TRK
= V
OUT_LDO
TO TRACK A VOLTAGE HIGHER THAN
V
OUT_LDO
:
V
OUT_TRK
= V
OUT_LDO
x (R3 + R4) / R4,
R3 + R4 < V
OUT_TRK
/ 20μA
(a)
(b)
IN
LDO
OUTPUT
V
IN
OUT_TRK
OUT_LDO
TRACKER
OUTPUT
FB_TRK
ADJ
MAX15008
MAX15010
TRACK
IN
R3
V
IN
OUT_TRK
ADJ
TRACKER
OUTPUT
MAX15008
MAX15010
R4
FB_TRK
TRACK
TO TRACK A VOLTAGE LOWER THAN V
OUT_LDO
:
V
OUT_TRK
= V
OUT_LDO
x R6 / (R5 + R6),
R5 + R6 < V
OUT_LDO
/ 20μA
TO TRACK A GENERIC VOLTAGE V
X
:
V
OUT_TRK
= V
X
x (R6 / (R5 + R6)) x ((R3 + R4) / R4),
R5 + R6 < V
X
/ 20μA, R3 + R4 < V
OUT_TRK
/ 20μA
R5
(c)
(d)
V
X
Figure 4. Tracker Input and Feedback Adjustment
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
MAX15008/MAX15010
External MOSFET Selection
Select the external MOSFET with adequate voltage
rating, V
DSS
, to withstand the maximum expected load-
dump input voltage. The on-resistance of the MOSFET,
R
DS(ON)
, should be low enough to maintain a minimal
voltage drop at full load, limiting the power dissipation
of the MOSFET.
During regular operation, the power dissipated by the
MOSFET is:
P
NORMAL
= I
LOAD
2
x R
DS(ON)
Normally, this power loss is small and is safely handled
by the MOSFET. However, when operating the
MAX15008 in overvoltage-limiter mode under pro-
longed or frequent overvoltage events, select an exter-
nal MOSFET with an appropriate power rating.
During an overvoltage event, the power dissipation in
the external MOSFET is proportional to both load cur-
rent and to the drain-source voltage, resulting in high
power dissipated in the MOSFET (Figure 7). The power
dissipated across the MOSFET is:
P
OV_LIMITER
= V
Q1
x I
LOAD
where V
Q1
is the voltage across the MOSFET’s drain
and source during overvoltage-limiter operation, and
I
LOAD
is the load current.
Overvoltage-Limiter Mode
Switching Frequency
When the MAX15008 is configured in overvoltage-
limiter mode, the external n-channel MOSFET is subse-
quently switched on and off during an overvoltage
event. The output voltage at SOURCE resembles a
periodic sawtooth waveform. Calculate the period of
the waveform, t
OVP
, by summing three time intervals
(Figure 8):
t
OVP
= t
1
+ t
2
+ t
3
where t
1
is the V
SOURCE
output discharge time, t
2
is the
GATE delay time, and t
3
is the V
SOURCE
output charge time.
During an overvoltage event, the power dissipated
inside the MAX15008 is due to the gate pulldown cur-
rent, I
GATEPD
. This amount of power dissipation is
worse when I
SOURCE
= 0 (C
SOURCE
is discharged only
by the internal current sink).
The worst-case internal power dissipation contribution
in overvoltage-limiter mode, P
OVP
, in watts can be
approximated using the following equation:
where V
OV
is the overvoltage threshold voltage in volts
and I
GATEPD
is the 63mA (typ) GATE pulldown current.
Output Discharge Time (t
1
)
When the voltage at SOURCE exceeds the adjusted
overvoltage threshold, GATE’s internal pulldown is
enabled until V
SOURCE
drops by 4%. The internal cur-
rent sink, I
GATEPD
, and the external load current,
I
LOAD
, discharge the external capacitance from
SOURCE to ground.
PV I
t
t
OVP OV GATEPD
OVP
=×× ×098
1
.
Automotive 300mA LDO Voltage Regulators
with Tracker Output and Overvoltage Protector
18 ______________________________________________________________________________________
t
2
t
1
t
OVP
t
3
GATE
SOURCE
Figure 8. MAX15008 Timing Diagram
IN
FB_PROT
SGND
GATE
SOURCE
TVS
MAX15008
LOAD
I
LOAD
+ V
Q1
-
V
SOURCE
V
SOURCE
V
OV
V
MAX
Figure 7. Power Dissipated Across MOSFETs During an
Overvoltage Fault (Overvoltage Limiter Mode)
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24

MAX15010ATJ+

Mfr. #:
Buy MAX15010ATJ+
Manufacturer:
Maxim Integrated
Description:
LDO Voltage Regulators Automotive 300mA w/Tracker Output
Lifecycle:
New from this manufacturer.
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