Datasheet

2.5 3.0 3.5 4.0 4.5 5.0 5.5
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
EN THRESHOLDS (V)
VIN (V)
Rising TH -40°C
Falling TH -40°C
Rising TH 25°C
Falling TH 25°C
Rising TH 125°C
Falling TH 125°C
2.8 3.2 3.6 4.0 4.4 4.8 5.2
0
100
200
300
400
500
600
700
800
900
TOFF-MIN (ns)
VIN (V)
VOUT = -0.9V
VOUT = -1.5V
VOUT = -2.5V
VOUT = -3.3V
VOUT = -5.0V
LMR70503
www.ti.com SNVS850A –JUNE 2012–REVISED APRIL 2013
The built-in T
OFF-MIN
time is a function of both V
IN
and V
OUT
, as shown in Figure 34.
Figure 34. Minimum Off Time vs. V
IN
at room temperature
Enable And UVLO
The LMR70503 features an enable (EN) pin and associated comparator to allow the user to easily sequence the
LMR70503 from an external voltage rail, or to manually set the input UVLO threshold. Enable threshold levels
are referred to the LMR70503 ground, instead of the lowest potential: the negative output voltage. Enable turning
on (rising) and turning off (falling) thresholds are shown in Figure 35.
Figure 35. Enable Rising And Falling Thresholds vs. V
IN
It is important to ensure that a valid input voltage (2.8 V ≤ V
IN
≤ 5.5 V) is present on the VIN pin before the EN
input is asserted. Also, as stated in the Absolute Maximum Ratings section of this data sheet, the voltage on the
EN pin must always be less than V
IN
. This applies to both static and dynamic operation, and during start up and
shut down sequences. If these precautions are not followed, an internal test mode may be activated; possibly
damaging the regulator. The EN input must not be left floating. A resistor divider can be added from VIN to EN if
an external enable signal is not available.
An input under voltage lock-out (UVLO) circuit prevents the regulator from turning on when the input voltage is
not great enough to properly bias the internal circuitry. The typical UVLO rising threshold is 2.55 V and typical
hysteresis band is 0.13 V.
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