MAX1572 Datasheet, PDF (7/11 Pages) Maxim Integrated Products – 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET

800mA, 2MHz, PWM DC-to-DC
Step-Down Converter with RESET
Pin Description
PIN
NAME
FUNCTION
1
RESET ^{Active-Low RESET Output. Open-drain output with internal 14kΩ pullup to OUT. RESET is driven LOW in}
shutdown.
2
3, 5, 11
4
6
7
8
9
10
12
—
Soft-Start Control. Connect a capacitor from SS to GND to set the soft-start time. Use a 1000pF or larger
SS capacitor to eliminate inrush current during startup. With greater than 10µF total output capacitance, increase
C_SS to C_OUT/10,000 for soft-start. In shutdown, SS is discharged internally with 100Ω to GND.
GND Ground. Connect all ground pins to the exposed paddle.
OUT ^{Output Sense Input. Connect to the output of the regulator. In shutdown, OUT is discharged internally with}
14kΩ to GND.
EN2 Enable/Mode Control Input 2. See Table 1.
PGND Power Ground. Connect to exposed paddle.
LX Inductor Connection. LX is high impedance in shutdown.
BATT Supply Voltage Input. Connect to a 2.6V to 5.5V source. Connect a 10µF ceramic capacitor from BATT to GND.
EN1 Enable/Mode Control Input 1. See Table 1.
ABATT Analog Supply Input. Connect to BATT through a 10Ω resistor. Connect a 0.1µF capacitor from ABATT to GND.
Exposed
Paddle
Exposed Paddle. Connect to GND and PGND.
Table 1. Mode Select Truth Table
MODE
EN1
EN2
Shutdown
0
0
Pulse group
0
1
Pulse skip
1
0
Forced PWM
1
1
A zero represents EN_ being driven low or connected to GND.
A 1 represents EN_ being driven high or connected to BATT.
Detailed Description
Figure 1 is the functional diagram.
PWM Control Scheme
The MAX1572 uses a 2MHz fixed-frequency, pulse-
width-modulated (PWM), current-mode control scheme.
The heart of the current-mode PWM controller is an
open-loop comparator that compares the error amp
voltage-feedback signal against the sum of the ampli-
fied current-sense signal and the slope compensation
ramp. At each rising edge of the internal clock, the
internal high-side P-channel MOSFET turns on until the
PWM comparator trips. During this on-time, current
ramps up through the inductor, sourcing current to the
EN2
MODE
CLOCK
2MHz
SELECT
EN1
CURRENT
SENSE
SLOPE
COMP
PWM
CONTROL
MAX1572
RESET ^RESET
TIMER
170ms
EA
REFERENCE
ABATT
BATT
LX
PGND
OUT
0.1µF
10Ω
INPUT
2.6V TO 5.5V
10µF
OUTPUT
0.75V TO 2.5V
800mA
2.2µH
COUT
GND
THERMAL
SHUTDOWN
SS
1000pF
Figure 1. Functional Diagram
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