MAX15008 Datasheet, PDF (16/23 Pages) Maxim Integrated Products – Automotive 300mA LDO Voltage Regulators with Tracker Output and Overvoltage Protector

Automotive 300mA LDO Voltage Regulators
with Tracker Output and Overvoltage Protector
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).
V_IN
IN
OUT_LDO
ADJ
MAX15008
MAX15010
TRACK
OUT_TRK
FB_TRK
TO TRACK V_{OUT_LDO}:
V_{OUT_TRK} = V_{OUT_LDO}
LDO
OUTPUT
TRACKER
OUTPUT
(a)
V_IN
IN
OUT_LDO
LDO
OUTPUT
R5
MAX15008
MAX15010 ADJ
TRACK
R6
OUT_TRK
FB_TRK
TRACKER
OUTPUT
V_IN
IN
OUT_LDO
LDO
OUTPUT
MAX15008 ^ADJ
MAX15010
TRACK
OUT_TRK
TRACKER
OUTPUT
R3
FB_TRK
R4
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
(b)
R5
V_IN
IN
ADJ
V_X
R6
MAX15008
MAX15010
TRACK
OUT_TRK
TRACKER
OUTPUT
R3
FB_TRK
R4
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
(c)
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
(d)
Figure 4. Tracker Input and Feedback Adjustment
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