zl2005 Intersil Corporation, zl2005 Datasheet - Page 12

• Manufacturer Part Number: zl2005
• Description: Digital-dc? Integrated Power Management And Conversion Ic
• Manufacturer: Intersil Corporation

4.2 Power Conversion Overview
The ZL2005 operates as a voltage-mode, synchronous
buck converter with a selectable, constant frequency
Pulse Width Modulator (PWM) control scheme that
uses external MOSFETs, inductor and capacitors to
perform power conversion.
Figure 6 illustrates the basic synchronous buck con-
verter topology showing the primary power train com-
ponents. This converter is also called a step-down
converter, as the output voltage must always be lower
than the input voltage.
Figure 6. Synchronous Buck Converter
SMBUS
ZL2005
{
SA(0,1)
SALRT
SYNC
TACH
VTRK
SDA
SCL
VR
BST
GH
SW
GL
CB
REFCN
DB
PG
V
12
IN
COMMUNICATION
QH
SYNC
QL
EN
GEN
L1
MGN ILIM(0,1) SS(0,1) DLY(0,1) V(0,1)
DAC
C
IN
POWER MANAGEMENT
Figure 5. ZL2005 Detailed Block Diagram
C
V
OUT
COMPENSATOR
OUT
PLL
DIGITAL
INPUT VOLTAGE BUS
ADC
ADC
ZL2005
ADC
D-PWM
MUX
FC(0,1)
NLR
In its most simple configuration, the ZL2005 requires
two external N-channel power MOSFETs, one for the
top control MOSFET (QH) and one for the bottom
synchronous MOSFET (QL). The amount of time that
QH is on as a fraction of the total switching period is
known as the duty cycle D, which is described by the
following equation:
DRIVERS
MOSFET
VR LDO
SENSOR
TEMP
VDD
Σ
+
-
VSEN
VDD
BST
VR
SW
GH
GL
D
ISENB
ISENA
VSEN
XTEMP
≈
V
--------------- -
V
OUT
IN
February 18, 2009
V
OUT
FN6848.0