SIP21106DT-33-E3(2007) 데이터 시트보기 (PDF) - Vishay Semiconductors
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SIP21106DT-33-E3 Datasheet PDF : 13 Pages
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SiP21106/7/8
Vishay Siliconix
New Product
DETAILED DESCRIPTION
As shown in the block diagram, the circuit consists of a band-
gap reference, error amplifier, P-Channel pass transistor and
an internal feedback resistor voltage divider, which is used to
monitor and control the output voltage.
A constant 1.2 V bandgap reference voltage is applied to the
non-inverting input of the error amplifier. The error amplifier
compares this reference with the feedback voltage on its
inverting input and amplifies the difference. If the feedback
voltage is lower than the reference voltage, the pass-transis-
tor gate is pulled low. This increases the PMOS's gate to
source voltage and allows more current to pass through the
transistor to the output which increases the output voltage.
Conversely, if the feedback voltage is higher than the refer-
ence voltage, the pass transistor gate is pulled high,
decreasing the gate-to-source voltage, thereby allowing less
current to pass to the output and causing it to drop.
Internal P-Channel Pass Transistor
A 0.9 Ω (typical) P-Channel MOSFET is used as the pass
transistor for the SiP21106/7/8 part series. The MOSFET
transistor offers many advantages over the more, formerly,
common PNP pass transistor designs, which ultimately
result in longer battery lifetime. The main disadvantage of
PNP pass transistors is that they require a certain base cur-
rent to stay on, which significantly increases under heavy
load conditions. In addition, during dropout, when the pass
transistor saturates, the PNP regulators waste considerable
current. In contrast, P-Channel MOSFETS require virtually
zero-base drive and do not suffer from the stated problems.
These savings in base drive current translate to lower quies-
cent current which is typical around 35 µA as shown in the
Typical Characteristics.
Shutdown and Auto-Dischage/No-Discharge
Bringing the EN voltage low will place the part in shutdown
mode where the device output enters a high-impedance
state and the quiescent current is reduced to below 1 µA,
reducing the drain on the battery in standby mode and
increasing standby time. Connect EN pin to input for normal
operation. The output has an internal pull down to discharge
the output to ground when the EN pin is low. The internal pull
down is a 100 Ω typical resistor, which can discharge a 1 µF
in less than 1 ms. Refer to Typical Operating Waveforms for
turn-off waveforms.
Output Voltage Selection
The SiP21106 has fixed voltage outputs that are preset to
voltages from 1.8 V to 4.6 V (see Ordering Information).
VIN
1.2 V
Reference
+
Error-Amp
-
VOUT
R1
R2
Figure 4.
The SiP21108 has a user-adjustable output that can be set
through the resistor feedback network consisting of R1 and
R2. R2 range of 100K to 400K is recommended to be
consistent with ground current specification. R1 can then be
determined by the following equation:
R1
=
R
2
x
(
VOUT
V ref
-
1)
Where Vref is typically 1.2005 V. Use 1 % or better resistors
for better output voltage accuracy (see Figure 4).
Current Limit
The SiP21106/7/8 include a current limit block which moni-
tors the current passing through the pass transistor through
a current mirror and controls the gate voltage of the MOS-
FET, limiting the output current to 330 mA (typical). This cur-
rent limit feature allows for the output to be shorted to ground
for an indefinite amount of time without damaging the device.
Thermal-Overload Protection
The thermal overload protection limits the total power dissi-
pation and protects the device from being damaged. When
the junction temperature exceeds TJ = 150 °C, the device
turns the P-Channel pass transistor off allowing the device to
cool down. Once the temperature drops by about 20 °C, the
thermal sensor turns the pass transistor on again and
resumes normal operation. Consequently, a continuous ther-
mal overload condition will result in a pulsed output. It is gen-
erally recommended to not exceed the junction temperature
rating of 125 °C for continuous operation.
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Document Number: 74442
S-70067–Rev. B, 22-Jan-07
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