LP3921 Datasheet, PDF (25/34 Pages) National Semiconductor (TI) – Battery Charger Management and Regulator Unit with Integrated Boomer® Audio Amplifier

where the temperature will change significantly above or be-
low 25ºC.
NO-LOAD STABILITY
The LDO's on the LP3921 will remain stable in regulation with
no external load.
TABLE 19. LDO Output Capacitors Recommended Specification
Symbol
C_o(LDO1)
C_o(LDO2)
C_o(LDO3)
C_o(LDO4)
C_o(LDO5)
C_o(LDO6)
C_o(LDO7)
Parameter
Capacitance
Capacitance
Capacitance
Capacitance
Capacitance
Capacitance
Capacitance
Capacitor Type
X5R. X74
X5R. X74
X5R. X74
X5R. X74
X5R. X74
X5R. X74
X5R. X74
Limit
Typ
Min
Max
1.0
0.7
2.2
1.0
0.7
2.2
1.0
0.7
2.2
1.0
0.7
2.2
1.0
0.7
2.2
1.0
0.7
2.2
1.0
0.7
2.2
Units
µF
µF
µF
µF
µF
µF
µF
Note: The capacitor tolerance should be 30% or better over
the full temperature range. X7R or X5R capacitors should be
used. These specifications are given to ensure that the ca-
pacitance remains within these values over all conditions
within the application. See Capacitor Characteristics section
in Application Information.
Thermal Shutdown
The LP3921 has internal limiting for high on-chip tempera-
tures caused by high power dissipation etc. This Thermal
Shutdown, TSD, function monitors the temperature with re-
spect to a threshold and results in a device power-down.
If the threshold of +160°C has been exceeded then the device
will power down. Recovery from this TSD event can only be
initiated after the chip has cooled below +115°C. This device
recovery is controlled by the APU_TSD_EN bit (bit 1) in con-
trol register MISC, 8h'1C. See Table 21. If the APU_TSD_EN
is set low then the device will shutdown requiring a new start
up event initiated by PWR_ON, HF_PWR, or CHG_IN. If
APU_TSD_EN is set high then the device will power up au-
tomatically when the shutdown condition clears. In this case
the control register settings are preserved for the device
restart.
The threshold temperature for the device to clear this TSD
event is 115°C. This threshold applies for any start up thus
the device temperature must be below this threshold to allow
a start up event to initiate power up.
Further Register Information
STATUS REGISTER READ ONLY
TABLE 20. Register Address 8h'0C: Status
Bit Name
Function (if bit = '1')
7 PWR_ON_TRI PMU startup is initiated by
G
PWR_ON.
6 HF-PWR-TRIG PMU startup is initiated by
PWR_TRIG.
5 CHG_IN_TRIG PMU startup is initiated by CHG_IN.
MISC CONTROL REGISTER
TABLE 21. Register Address 8h'1C: Misc.
Bit Name
Function (if bit = '1')
1 APU_TSD_EN 1b'0: Device will shut down
completely if thermal shutdown
occurs. Requires a new startup
event to restart the PMU.
1b'1: Device will start up
automatically after thermal
shutdown condition is removed.
(Device tries to keep its internal
state.)
0 PWR_HOLD_D 1b'0: If PWR_HOLD is low for 35 ms,
ELAY
the device will shutdown. (Default)
1b'1: If PWR_HOLD is low for 350
ms, the device will shut down.
Bits <7...2> are not used.
Differential Amplifier Explanation
TABLE 22. Register Address 8h'19 Audio_Amp
Bit Name
Function
(if the powerup default is "amplifier
disabled")
0 amp_en Bit set to '0' - amplifier disabled
Bit set to '1' - amplifier enabled
The LP3921 contains a fully differential audio amplifier that
features differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a
common mode feedback amplifier that adjusts the output volt-
ages so that the average value remains VDD/2. When setting
the differential gain, the amplifier can be considered to have
"halves". Each half uses an input and feedback resistor (Ri1
and RF1) to set its respective closed-loop gain. (See Figure
9.) With Ri1 = Ri2 and RF1 = RF2, the gain is set at -RF / Ri
for each half. This results in a differential gain of:
Bits <4...0> are not used.
AVD = −RF/Ri
(1)
It is extremely important to match the input resistors to each
other, as well as the feedback resistors to each other for best
amplifier performance. A differential amplifier works in a man-
ner where the difference between the two input signals is
amplified. In most applications, this would require input sig-
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