Datasheet

TPS54380
SLVS454B − JANUARY 2003 − REVISED FEBRUARY 2005
www.ti.com
11
Figure 14
−60
−50
−40
−30
−20
−10
0
10
20
30
40
50
60
100 1 k 10 k 100 k 1 M
−180
−150
−120
−90
−60
−30
0
30
60
90
120
150
180
Gain − dB
f − Frequency − Hz
MEASURED LOOP RESPONSE
Phase − Degrees
Gain
Phase
Figure 15
25
35
45
55
65
75
85
95
105
115
125
01234
− Ambient Temperature −
AMBIENT TEMPERATURE
vs
LOAD CURRENT
I
L
− Load Current − A
C
°
T
A
Safe Operating Area
(1)
V
I
= 3.3 V
V
I
= 5 V
Fi
g
ure 16
Time − 1 µs/div
OUTPUT RIPPLE VOLTAGE
Output Ripple Voltage − 10 mV/div
Figure 17
100 µs/div
20 mV/div
LOAD TRANSIENT RESPONSE
1 A/div
I = 0.75 A to 2.25 A
Figure 18
2 V/div
Vcore
V I/O
V I/O ~Enable
START-UP TIMING
2 ms/div
1 V/div
Figure 19
2 V/div
Vcore
V I/O
V I/O ~Enable
POWER-DOWN TIMING
2 ms/div
1 V/div
(1)
Safe operating area is applicable to the test board conditions in the Dissipation Ratings table.
DETAILED DESCRIPTION
UNDERVOLTAGE LOCKOUT (UVLO)
The TPS54380 incorporates an undervoltage lockout
circuit to keep the device disabled when the input voltage
(VIN) is insufficient. During power up, internal circuits are
held inactive until VIN exceeds the nominal UVLO
threshold voltage of 2.95 V. Once the UVLO start threshold
is reached, device start-up begins. The device operates
until VIN falls below the nominal UVLO stop threshold of
2.8 V. Hysteresis in the UVLO comparator, and a 2.5-µs
rising and falling edge deglitch circuit reduce the likelihood
of shutting the device down due to noise on VIN.
TRACKIN/INTERNAL SLOW-START
The internal slow-start circuit provides start-up slope
control of the output voltage. The nominal internal
slow-start rate is 25 V/ms. When the voltage on TRACKIN
rises faster than the internal slope or is present when
device operation is enabled, the output rises at the internal
rate. If the reference voltage on TRACKIN rises more
slowly, then the output rises at about the same rate as
TRACKIN.
Once the voltage on the TRACKIN pin is greater than the
internal reference of 0.891 V, the multiplexer switches the
noninverting node to the high-precision reference.
ENABLE (ENA)
The enable pin, ENA, provides a digital control enable or
disable (shutdown) for the TPS54380. An input voltage of
1.4 V or greater ensures that the TPS54380 is enabled. An
input of 0.82 V or less ensures that device operation is
disabled. These are not standard logic thresholds, even
though they are compatible with TTL outputs.
When ENA is low, the oscillator, slow-start, PWM control
and MOSFET drivers are disabled and held in an initial
state ready for device start-up. On an ENA transition from
low to high, device start-up begins with the output starting
from 0 V.