MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER
When the silicon die temperature exceeds
Startup and Shutdown
150°C, the whole chip shuts down: The HS-FET
and LS-FET turn off, and the SS pin voltage
goes low. When the temperature drops below
the lower threshold—typically 140°C—the chip
restarts with an SS.
When VIN and EN exceed their respective
thresholds, the chip starts. The reference block
starts first, generating stable reference voltages
and currents, and then the internal regulator is
enabled. The regulator provides a stable power
supply for the rest of the device.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver has several
features to ensure stability and functionality,
such as its own UVLO protection with a rising
threshold of 2.2V and a hysteresis of 150mV.
An external bootstrap capacitor—regulated
internally by VIN through D1, M1, C4, L1 and C2
(see Figure 4)—powers this driver. U1
regulates M1 to maintain a 5V BST voltage
across C4 whenever (VIN-VSW) > 5V.
Three events can shut down the chip: EN low,
VIN low, and thermal shutdown. In shutdown,
the signaling path shuts down first to avoid
triggering any faults. Then the COMP voltage
and the internal supply rail are pulled down.
The floating driver is not subject to this
shutdown command.
D1
V
IN
M1
BST
U1
5V
C4
V
OUT
SW
L1
C2
Figure 4: Internal Bootstrap Charging Circuit
MPQ28261 Rev. 1.12
10/10/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
14
MPS [ MONOLITHIC POWER SYSTEMS ]
