Datasheet

+
V
IN
UVLO
VIN
R
UV1
C
IN
R
UV2
2
3
LM5019
LM5019
SNVS788E –JANUARY 2012–REVISED DECEMBER 2013 www.ti.com
N-Channel Buck Switch and Driver
The LM5019 integrates an N-Channel Buck switch and associated floating high voltage gate driver. The gate
driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 0.01
uF ceramic capacitor connected between the BST pin and the SW pin provides the voltage to the driver during
the on-time. During each off-time, the SW pin is at approximately 0 V, and the bootstrap capacitor charges from
V
CC
through the internal diode. The minimum off-timer, set to 144 ns, ensures a minimum time each cycle to
recharge the bootstrap capacitor.
Synchronous Rectifier
The LM5019 provides an internal synchronous N-Channel MOSFET rectifier. This MOSFET provides a path for
the inductor current to flow when the high-side MOSFET is turned off.
The synchronous rectifier has no diode emulation mode, and is designed to keep the regulator in continuous
conduction mode even during light loads which would otherwise result in discontinuous operation.
Undervoltage Detector
The LM5019 contains a dual level Undervoltage Lockout (UVLO) circuit. When the UVLO pin voltage is below
0.66 V, the controller is in a low current shutdown mode. When the UVLO pin voltage is greater than 0.66 V but
less than 1.225 V, the controller is in standby mode. In standby mode the V
CC
bias regulator is active while the
regulator output is disabled. When the V
CC
pin exceeds the V
CC
undervoltage threshold and the UVLO pin
voltage is greater than 1.225 V, normal operation begins. An external set-point voltage divider from V
IN
to GND
can be used to set the minimum operating voltage of the regulator.
UVLO hysteresis is accomplished with an internal 20 μA current source that is switched on or off into the
impedance of the set-point divider. When the UVLO threshold is exceeded, the current source is activated to
quickly raise the voltage at the UVLO pin. The hysteresis is equal to the value of this current times the resistance
R
UV2
.
UVLO V
CC
Mode Description
<0.66 V Shutdown V
CC
Regulator Disabled.
Switcher Disabled.
0.66 V – 1.225 V Standby V
CC
Regulator Enabled
Switcher Disabled.
>1.225 V V
CC
<4.5 V Standby V
CC
Regulator Enabled.
Switcher Disabled.
V
CC
>4.5 V Operating V
CC
enabled.
Switcher enabled.
If the UVLO pin is wired directly to the V
IN
pin, the regulator will begin operation once the V
CC
undervoltage is
satisfied.
Figure 14. UVLO Resistor Setting
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