LM828M5/NOPB National Semiconductor, LM828M5/NOPB Datasheet - Page 6

• Manufacturer Part Number: LM828M5/NOPB
• Description: IC SW CAP/INV ADJ 25MA SOT23-5
• Manufacturer: National Semiconductor
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of LM828M5/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -1.8 ~ -5.5 V
• Current - Output: 25mA
• Frequency - Switching: 12kHz
• Voltage - Input: 1.8 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Power - Output: 240mW
• Dc: 06+
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM828M5/NOPBTR

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Pin Descriptions
Circuit Description
The LM828 contains four large CMOS switches which are
switched in a sequence to invert the input supply voltage. En-
ergy transfer and storage are provided by external capacitors.
Figure 3
S
During this time interval, switches S
second time interval, S
S
cycles, the voltage across C
anode of C
of C
voltage drop when a load is added is determined by the par-
asitic resistance (R
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 sup-
ply voltage. The voltage inverter circuit uses only two external
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
a function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and the
Pin
1
2
1
2
3
4
5
and S
and S
2
equals −(V+) when there is no load current. The output
3
4
illustrates the voltage conversion scheme. When
FIGURE 3. Voltage Inverting Principle
2
are closed, C
are closed, C
is connected to ground, the output at the cathode
Name
CAP−
CAP+
GND
OUT
V+
ds(on)
1
1
and S
1
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.
of the MOSFET switches and the
charges to the supply voltage V+.
is charging C
2
will be pumped to V+. Since the
3
are open; at the same time,
2
and S
2
. After a number of
4
are open. In the
out
10013726
, is
6
ESR of both C
and discharging C
rent, the effect of the ESR of the pumping capacitor C
multiplied by four in the output resistance. The output capac-
itor C
equal to the output current, therefore, this ESR term only
counts once in the output resistance. A good approximation
of R
where R
MOSFET switches shown in
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
ripple, and the converter efficiency. Low ESR capacitors (fol-
lowing table) are recommended to maximize efficiency, re-
duce the output voltage drop and voltage ripple.
out
Function
L
2
2
is charging and discharging at a current approximately
R
is:
Q
out
SW
(V+) is the quiescent power loss of the IC device,
2
is the conversion loss associated with the switch
is the sum of the ON resistance of the internal
:
1
and C
1
is approximately twice as the output cur-
2
. Since the switching current charging
Figure
out
3.
R
out
), the output voltage
1
will be