Datasheet
0 10 20 30 40 50 60 70 80 90
300
400
500
600
700
800
SOFT OFF RAMP TIME (90% TO 10%) (s)
TEMPERATURE (°C)
VIN = 2.8 V
VIN = 4.0 V
VIN = 5.0 V
LMR70503
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SNVS850A –JUNE 2012–REVISED APRIL 2013
Figure 38. Soft Off Time (90% To 10% Vout) vs. Temperature, V
OUT
= -5.5 V, No Load
Short Circuit Protection
Peak current mode control has inherent short circuit protection. The protection level is the maximum inductor
current limit level. It varies with V
IN
and temperature due to propagation delays. The minimum off-time limits the
current going through the inductor during a short circuit condition.
Over-Temperature Protection
Internal thermal shutdown (TSD) circuitry protects the LMR70503 should the maximum junction temperature be
exceeded. This protection is activated at 165 °C (typical), with the result that the regulator will shutdown until the
junction temperature drops below 155 °C (typical). Of course the LMR70503 must not be operated continuously
above 125 °C.
Design Guide
Output Voltage Setting
The output voltage of the LMR70503 is programmable by the voltage divider resistors. The reference voltage is
typically 1.19 V. To avoid overloading the V
REF
circuity, the resistor R
T
tied between V
REF
and FB is
recommended to be between 20 kΩ and 100 kΩ. With a selected R
T
, R
B
tied between V
OUT
and FB can be found
by
R
B
= R
T
* |V
OUT
| / V
REF
(3)
A feed-forward capacitor C
FF
can be used between V
OUT
and FB nodes to improve transient performance. 10 pF
C0G, NP0 type of capacitor is recommended in LMR70503 applications.
Input Capacitor And Output Capacitor Selection
The input capacitor selection is based on both input voltage ripple and RMS current. Good quality input
capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the regulator current
during switch on-time. Low ESR ceramic capacitors are preferred. A minimum value of 10μF at 6.3 V, is required
at the input of the LMR70503. Larger values of input capacitance are desirable to reduce voltage ripple and
noise on the input supply.
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