LMZ21701_15 Datasheet, PDF (8/37 Pages) Texas Instruments – LMZ21701 1 A SIMPLE SWITCHER® Nano Module with 17 V Maximum Input Voltage

LMZ21701
SNVS853D – AUGUST 2012 – REVISED NOVEMBER 2014
8 Detailed Description
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8.1 Overview
The LMZ21701 SIMPLE SWITCHER^® Nano Module is an easy-to-use step-down DC-DC solution capable of
driving up to 1000 mA load in space-constrained applications. Only an input capacitor, an output capacitor, a
softstart capacitor, and two resistors are required for basic operation. The Nano Module comes in 8-pin DFN
footprint package with an integrated inductor. The LMZ21701 architecture is based on DCS-Control™ (Direct
Control with Seamless Transition into Power Save Mode). This architecture combines the fast transient response
and stability of hysteretic type converters along with the accurate DC output regulation of voltage mode and
current mode regulators.
The LMZ21701 architecture uses Pulse Width Modulation (PWM) mode for medium and heavy load requirements
and Power Save Mode (PSM) at light loads for high efficiency. In PWM mode the switching frequency is
controlled over the input voltage range. The value depends on the output voltage setting and is typically reduced
at low output voltages to achieve higher efficiency. In PSM the switching frequency decreases linearly with the
load current. Since the architecture of the device supports both operation modes (PWM and PSM) in a single
circuit building block, the transition between the modes of operation is seamless with minimal effect on the output
voltage.
8.2 Functional Block Diagram
VIN
EN
SS
GND
LDO
BYPASS
5V LDO
400kŸ
THERMAL
SHUTDOWN
SOFTSTART
CURRENT AND
TRACKING
UVLO
HIGH SIDE
SWITCH
HIGH SIDE
CURRENT
LIMIT
HIGH SIDE DRIVER
WITH INTERNAL BOOTSTRAP
CONTROL LOGIC
LOW SIDE
DRIVER
LOW SIDE
CURRENT
LIMIT
ZERO
CURRENT
DETECT
INDUCTOR
2.2µ H
LOW SIDE
SWITCH
tON TIMER
COMPARATOR
DIRECT CONTROL
&
COMPENSATION
25pF
6.6V
CLAMP
CFF
ERROR
AMPLIFIER
VREF
+
-
VOUT
PG
VOS
FB
8
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