LM2670S-ADJ/NOPB National Semiconductor, LM2670S-ADJ/NOPB Datasheet - Page 6

• Manufacturer Part Number: LM2670S-ADJ/NOPB
• Description: IC REG SIMPLE SWITCHER TO-263-7
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2670S-ADJ/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 37 V
• Current - Output: 3A
• Frequency - Switching: 260kHz
• Voltage - Input: 8 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Voltage: 37V
• Output Current: 3A
• No. Of Pins: 7
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 3 - 168 Hours
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2670S-ADJ; *LM2670S-ADJ/NOPB; LM2670S-ADJ

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Application Information
SIMPLE NEGATIVE VOLTAGE CONVERTER
The main application of LM2664 is to generate a negative
supply voltage. The voltage inverter circuit uses only two
external capacitors as shown in the Basic Application Cir-
cuits. 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
function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and ESR
of C
discharging C
the effect of the ESR of the pumping capacitor C
multiplied by four in the output resistance. The output ca-
pacitor C
mately equal to the output current, therefore, its ESR only
counts once in the output resistance. A good approximation
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.
Nichicon Corp.
AVX Corp.
Sprague
Sanyo
Murata
Taiyo Yuden
Tokin
out
1
and C
is:
SW
2
Manufacturer
is charging and discharging at a current approxi-
2
is the sum of the ON resistance of the internal
:
2
1
. Since the switching current charging and
is approximately twice as the output current,
(708)-843-7500
(803)-448-9411
(207)-324-4140
(619)-661-6835
(800)-831-9172
(800)-348-2496
(408)-432-8020
Phone
Low ESR Capacitor Manufacturers
1
out
will be
is a
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
Ceramic chip capacitors
Ceramic chip capacitors
Ceramic chip capacitors
6
SHUTDOWN MODE
A shutdown (SD ) pin is available to disable the device and
reduce the quiescent current to 1µA. Applying a voltage less
than 20% of V+ to the SD pin will bring the device into
shutdown mode. While in normal operating mode, the pin is
connected to V+.
CAPACITOR SELECTION
As discussed in the Simple Negative Voltage Converter
section, the output resistance and ripple voltage are depen-
dent 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
(Table 1) are recommended to maximize efficiency, reduce
the output voltage drop and voltage ripple.
L
2
R
Q
out
(V+) is the quiescent power loss of the IC device,
is the conversion loss associated with the switch
Capacitor Type
out
R
out
), the output volt-