lm2500506 National Semiconductor Corporation, lm2500506 Datasheet - Page 3

• Manufacturer Part Number: lm2500506
• Description: 2.5a Step-down Switching Regulator
• Manufacturer: National Semiconductor Corporation

Pin Descriptions
Pin(S)
13, 14
15, 16
17, 18
3, 4
10
11
12
19
1
2
5
6
7
8
9
COMP
RAMP
AGND
PGND
Name
SYNC
VCC
OUT
PRE
SW
SD
Vin
RT
SS
FB
IS
Output of the bias regulator
Shutdown or UVLO input
Input supply voltage
Oscillator synchronization input or output The internal oscillator can be synchronized to an external
Output of the internal error amplifier
Feedback signal from the regulated
output
Internal oscillator frequency set input
Ramp control signal
Analog ground
Soft-start
Output voltage connection
Power ground
Current sense
Switching node
Pre-charge assist for the bootstrap
capacitor
Description
3
Vcc tracks Vin up to 9V. Beyond 9V, Vcc is regulated to 7
Volts. A 0.1uF to 1uF ceramic decoupling capacitor is
required. An external voltage (7.5V – 14V) can be applied
to this pin to reduce internal power dissipation.
If the SD pin voltage is below 0.7V the regulator will be in a
low power state. If the SD pin voltage is between 0.7V and
1.225V the regulator will be in standby mode. If the SD pin
voltage is above 1.225V the regulator will be operational. An
external voltage divider can be used to set a line
undervoltage shutdown threshold. If the SD pin is left open
circuit, a 5µA pull-up current source configures the regulator
fully operational.
Nominal operating range: 7V to 42V
clock with an external pull-down device. Multiple LM25005
devices can be synchronized together by connection of their
SYNC pins.
The loop compensation network should be connected
between this pin and the FB pin.
This pin is connected to the inverting input of the internal
error amplifier. The regulation threshold is 1.225V.
The internal oscillator is set with a single resistor, connected
between this pin and the AGND pin. The recommended
frequency range is 50KHz to 500KHz.
An external capacitor connected between this pin and the
AGND pin sets the ramp slope used for current mode
control. Recommended capacitor range 50pF to 2000pF.
Internal reference for the regulator control functions
An external capacitor and an internal 10µA current source
set the time constant for the rise of the error amp reference.
The SS pin is held low during standby, Vcc UVLO and
thermal shutdown.
Connect directly to the regulated output voltage.
Low side reference for the PRE switch and the IS sense
resistor.
Current measurement connection for the re-circulating
diode. An internal sense resistor and a sample/hold circuit
sense the diode current near the conclusion of the off-time.
This current measurement provides the DC level of the
emulated current ramp.
The source terminal of the internal buck switch. The SW pin
should be connected to the external Schottky diode and to
the buck inductor.
This open drain output can be connected to SW pin to aid
charging the bootstrap capacitor during very light load
conditions or in applications where the output may be pre-
charged before the LM25005 is enabled. An internal pre-
charge MOSFET is turned on for 250ns each cycle just prior
to the on-time interval of the buck switch.
Application Information
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