LM82CIMQA National Semiconductor, LM82CIMQA Datasheet - Page 5

• Manufacturer Part Number: LM82CIMQA
• Description: IC,SSOP,16PIN
• Manufacturer: National Semiconductor

Specifications of LM82CIMQA

• Rohs Compliant: NO

Pin Description
Circuit Description
The LM828 contains four large CMOS switches which are
switched in a sequence to invert the input supply voltage.
Energy transfer and storage are provided by external capaci-
tors. Figure 2 illustrates the voltage conversion scheme.
When S
age V+. During this time interval, switches S
open. In the second time interval, S
same time, S
number of cycles, the voltage across C
V+. Since the anode of C
at the cathode of C
rent. The output voltage drop when a load is added is deter-
mined by the parasitic resistance (R
switches and the ESR of the capacitors) and the charge
transfer loss between capacitors.
Application Information
Simple Negative Voltage Converter
The main application of LM828 is to generate a negative
supply voltage. The voltage inverter circuit uses only two ex-
ternal capacitors as shown in the Basic Application Circuits.
The range of the input supply voltage is 1.8V to 5.5V.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistance. The
voltage source equals −(V+). The output resistance, R
Low ESR Capacitor Manufacturers
Pin
1
2
3
4
5
Nichicon Corp.
AVX Corp.
Sprague
Sanyo
1
Manufacturer
FIGURE 2. Voltage Inverting Principle
and S
2
Name
CAP−
CAP+
GND
OUT
and S
V+
3
are closed, C
2
equals −(V+) when there is no load cur-
4
are closed, C
2
is connected to ground, the output
Negative voltage output.
Power supply positive input.
Connect this pin to the negative terminal of the charge-pump capacitor.
Power supply ground input.
Connect this pin to the positive terminal of the charge-pump capacitor.
1
charges to the supply volt-
1
1
(708)-843-7500
(803)-448-9411
(207)-324-4140
(619)-661-6835
and S
is charging C
ds(on)
2
Phone
will be pumped to
3
of the MOSFET
are open; at the
2
and S
2
. After a
DS100137-26
out
4
are
, is
PL & PF series, through-hole aluminum electrolytic
TPS series, surface-mount tantalum
593D, 594D, 595D series, surface-mount tantalum
OS-CON series, through-hole aluminum electrolytic
5
a function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and the
ESR of both C
and discharging C
rent, the effect of the ESR of the pumping capacitor C
be multiplied by four in the output resistance. The output ca-
pacitor C
mately equal to the output current, therefore, this ESR term
only counts once in the output resistance. A good approxi-
mation of R
where R
MOSFET switches shown in Figure 2 .
High capacitance, low ESR capacitors will reduce the output
resistance.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, the capacitance and ESR of the output
capacitor C
Again, using a low ESR capacitor will result in lower ripple.
Capacitor Selection
The output resistance and ripple voltage are dependent on
the capacitance and ESR values of the external capacitors.
The output voltage drop is the load current times the output
resistance, and the power efficiency is
Where I
and I
on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the specifications of
the dropout voltage (which equals I
age ripple, and the converter efficiency. Low ESR capacitors
(following table) are recommended to maximize efficiency,
reduce the output voltage drop and voltage ripple.
L
Function
2
R
Q
SW
out
2
(V+) is the quiescent power loss of the IC device,
is charging and discharging at a current approxi-
2
is the conversion loss associated with the switch
out
is the sum of the ON resistance of the internal
:
1
is:
Capacitor Type
and C
1
is approximately twice as the output cur-
2
. Since the switching current charging
out
R
out
), the output volt-
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1
will