Datasheet
MODE/DATA
2V/Div
V
OUT1
:1.5V
V
OUT1
:1.1V
V
IN
3.8V
ACKN=off
I
OUT1
=150mA
REG_DEF_1_Low
V
OUT1
:200mV/Div
Timebase-100 s/Divm
TPS62420, TPS62421
SLVS676C –JUNE 2006–REVISED JUNE 2010
www.ti.com
V
OUT1
CHANGE WITH EASYSCALE
Figure 25.
DETAILED DESCRIPTION
OPERATION
The TPS62420 includes two synchronous step-down converters. The converters operate with typically 2.25MHz
fixed frequency pulse width modulation (PWM) at moderate to heavy load currents. If Power Save Mode is
enabled, the converters automatically enter Power Save Mode at light load currents and operate in PFM (Pulse
Frequency Modulation). During PWM operation the converters use a unique fast response voltage mode
controller scheme with input voltage feed-forward to achieve good line and load regulation allowing the use of
small ceramic input and output capacitors. At the beginning of each clock cycle initiated by the clock signal, the
P-channel MOSFET switch is turned on and the inductor current ramps up until the comparator trips and the
control logic turns off the switch.
Each converter integrates two current limits, one in the P-channel MOSFET and another one in the N-channel
MOSFET. When the current in the P-channel MOSFET reaches its current limit, the P-channel MOSFET is
turned off and the N-channel MOSFET is turned on. If the current in the N-channel MOSFET is above the
N-MOS current limit threshold, the N-channel MOSFET remains on until the current drops below its current limit.
The two DC-DC converters operate synchronized to each other. A 180° phase shift between converter 1 and
converter 2 decreases the input RMS current.
Converter 1
In the adjustable output voltage version TPS62420 the converter 1 output voltage can be set via an external
resistor network on PIN DEF_1, which operates as an analog input. In this case, the output voltage can be set in
the range of 0.6V to VIN V. The FB1 Pin must be directly connected to the converter 1 output voltage VOUT1. It
feeds back the output voltage directly to the regulation loop.
The output voltage of converter 1 can also be changed by the EasyScale serial Interface. This makes the device
very flexible for output voltage adjustment. In this case, the device uses an internal resistor network.
In the fixed default output voltage version like TPS62421, the DEF_1 Pin is configured as a digital input. The
converter 1 defaults to 1.2V or 1.8V depending on the level of DEF_1 pin. If DEF_1 is low the default is 1.2V; if
high, the default is 1.8V. With the EasyScale™ interface, the output voltage for each DEF_1 Pin condition (high
or low) can be changed.
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