STEP-DOWN SWITCHING REGULATOR
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Output of the bias regulator
2 SD Shutdown or UVLO input
3, 4 Vin Input supply voltage
5 SYNC Oscillator synchronization input or
6 COMP Output of the internal error amplifier
7 FB Feedback signal from the regulated
8 RT Internal oscillator frequency set input
9 RAMP Ramp control signal
10 AGND Analog ground
11 SS Soft-start
Output voltage connection
IS Current sense
SW Switching node
Pre-charge assist for the bootstrap
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
The internal oscillator can be synchronized to an external
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
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.