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PDF MAX1637 Data sheet ( Hoja de datos )
| Número de pieza | MAX1637 | |
| Descripción | Miniature / Low-Voltage / Precision Step-Down Controller | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-1321; Rev 1; 2/98
EVAALVUAAILTAIOBNLEKIT
Miniature, Low-Voltage,
Precision Step-Down Controller
General Description
The MAX1637 synchronous, buck, switch-mode power-
supply controller generates the CPU supply voltage in
battery-powered systems. The MAX1637 is a stripped-
down version of the MAX1636 in a smaller 16-pin QSOP
package. The MAX1637 is intended to be powered sep-
arately from the battery by an external bias supply (typi-
cally the +5V system supply) in applications where the
battery exceeds 5.5V. The MAX1637 achieves excellent
DC and AC output voltage accuracy. This device can
operate from a low input voltage (3.15V) and delivers the
excellent load-transient response needed by upcoming
generations of dynamic-clock CPUs.
Using synchronous rectification, the MAX1637 achieves
up to 95% efficiency. Efficiency is greater than 80%
over a 1000:1 load-current range, which extends bat-
tery life in system-suspend or standby mode. Excellent
dynamic response corrects output load transients
caused by the latest dynamic-clock CPUs within five
300kHz clock cycles. Powerful 1A on-board gate driv-
ers ensure fast external N-channel MOSFET switching.
The MAX1637 features a logic-controlled and synchro-
nizable, fixed-frequency, pulse-width-modulation
(PWM) operating mode. This reduces noise and RF
interference in sensitive mobile-communications and
pen-entry applications. Asserting the SKIP pin enables
fixed-frequency mode, for lowest noise under all load
conditions. For a stand-alone device that includes a
+5V VL linear regulator and low-dropout capabilities,
refer to the MAX1636 data sheet.
________________________Applications
Notebook Computers
Subnotebook Computers
Handy-Terminals, PDAs
__________________Pin Configuration
____________________________Features
o ±2% DC Accuracy
o 0.1% (typ) DC Load Regulation
o Adjustable Switching Frequency to 350kHz
o Idle Mode™ Pulse-Skipping Operation
o 1.10V to 5.5V Adjustable Output Voltage
o 3.15V Minimum IC Supply Voltage (at VCC pin)
o Internal Digital Soft-Start
o 1.1V ±2% Reference Output
o 1µA Total Shutdown Current
o Output Overvoltage Crowbar Protection
o Output Undervoltage Shutdown (foldback)
o Tiny 16-Pin QSOP Package
______________Ordering Information
PART
MAX1637EEE
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
16 QSOP
__________Typical Operating Circuit
VBIAS VBATT
VCC
SHDN
VGG
MAX1637
DH
BST
TOP VIEW
CSH 1
16 SKIP
CSL 2
FB 3
CC 4
MAX1637
15 LX
14 DH
13 BST
REF 5
12 PGND
SHDN 6
SYNC 7
GND 8
11 DL
10 VGG
9 VCC
QSOP
Idle Mode is a trademark of Maxim Integrated Products.
CC
REF
SKIP
SYNC
GND
LX
DL
PGND
CSH
CSL
FB
OUTPUT
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
1 page  
Miniature, Low-Voltage,
Precision Step-Down Controller
____________________________________Typical Operating Characteristics (continued)
(VOUT = 3.3V, TA = +25°C, unless otherwise noted.)
10
8
6
4
2
0
-2
-4
-6
-8
-10
0.01
LOAD REGULATION
vs. LOAD CURRENT
0.1 1
LOAD CURRENT (A)
REF LOAD-REGULATION ERROR
vs. REF LOAD CURRENT
0.6
0.5
DROPOUT VOLTAGE
vs. LOAD CURRENT
900
800
VOUT FORCED TO 3.27V
SYNC = VCC
700
0.4 600
500
0.3
400
0.2 300
200
0.1
100
00
10
0 10 20 30 40 50 60 70 80 90 100
0.01
REF LOAD CURRENT (µA)
0.1 1
LOAD CURRENT (A)
LOAD-TRANSIENT RESPONSE
(3.3V/3A, PWM MODE)
MAX1637 TOC11
LOAD-TRANSIENT RESPONSE
(1.8V, PWM MODE)
MAX1637 TOC12
10
VOUT
50mV/div
VOUT
50mV/div
4A
LOAD
2A CURRENT
0A
10A
5A LOAD CURRENT
0A
100µs/div
SWITCHING WAVEFORMS
(PWM MODE)
MAX1637-13
VOUT
20mV/div
SWITCHING WAVEFORMS
(PFM MODE)
MAX1637-14
VOUT = 1.7V
VOUT
50mV/div
100µs/div
SWITCHING WAVEFORMS
DROPOUT OPERATION
MAX1637-15
SYNC = VCC
VOUT
10mV/div
1µs/div
5V
VLX
0V
1A INDUCTOR
0A CURRENT
20µs/div
5V
VLX
0V
1A INDUCTOR
0A CURRENT
VOUT FORCED TO 3.27V
1µs/div
VLX
2V/div
1A
INDUCTOR
0A CURRENT
_______________________________________________________________________________________ 5
5 Page 
Miniature, Low-Voltage,
Precision Step-Down Controller
Idle Mode
When SKIP is low, idle-mode circuitry automatically
optimizes efficiency throughout the load-current range.
Idle mode dramatically improves light-load efficiency
by reducing the effective frequency, subsequently
reducing switching losses. It forces the peak inductor
current to ramp to 30% of the full current limit, deliver-
ing extra energy to the output and allowing subsequent
cycles to be skipped. Idle mode transitions seamlessly
to fixed-frequency PWM operation as load current
increases (Table 3).
Fixed-Frequency Mode
When SKIP is high, the controller always operates in
fixed-frequency PWM mode for lowest noise. Each pulse
from the oscillator sets the main PWM latch that turns on
the high-side switch for a period determined by the duty
factor (approximately VOUT / VIN). As the high-side switch
turns off, the synchronous rectifier latch is set; 60ns later,
the low-side switch turns on. The low-side switch stays on
until the beginning of the next clock cycle.
In PWM mode, the controller operates as a fixed-fre-
quency, current-mode controller in which the duty fac-
tor is set by the input/output voltage ratio. PWM mode
(SKIP = high) forces two changes on the PWM con-
troller. First, it disables the minimum-current compara-
tor, ensuring fixed-frequency operation. Second, it
changes the detection threshold for reverse-current
limit from 0mV to -100mV, allowing the inductor current
to reverse at light loads. This results in fixed-frequency
operation and continuous inductor-current flow. PWM
mode eliminates discontinuous-mode inductor ringing
and improves cross-regulation of transformer-coupled,
multiple-output supplies.
Table 3. SKIP PWM Table
SKIP
LOAD
CURRENT
MODE
DESCRIPTION
Low Light
Idle
Pulse-skipping, discontin-
uous inductor current
Low
Heavy
PWM
Constant frequency PWM,
continuous inductor current
High
Light
PWM
Constant frequency PWM,
continuous inductor current
High
Heavy
PWM
Constant frequency PWM,
continuous inductor current
The current-mode feedback system regulates the peak
inductor-current value as a function of the output volt-
age error signal. In continuous-conduction mode, the
average inductor current is nearly the same as the
peak current, so the circuit acts as a switch-mode
transconductance amplifier. This pushes the second
output LC filter pole, normally found in a duty-factor-
controlled (voltage-mode) PWM, to a higher frequency.
To preserve inner-loop stability and eliminate regenera-
tive inductor-current “staircasing,” a slope-compensa-
tion ramp is summed into the main PWM comparator to
make the apparent duty factor less than 50%.
The relative gains of the voltage-sense and current-
sense inputs are weighted by the values of the current
sources that bias four differential input stages in the
main PWM comparator (Figure 4). The voltage sense
into the PWM has been conditioned by an integrated
component of the feedback voltage, yielding excellent
DC output voltage accuracy. See the Output Voltage
Accuracy section for details.
VCC
R1 R2
TO PWM
LOGIC
CC FB
UNCOMPENSATED
HIGH-SPEED
LEVEL TRANSLATOR
AND BUFFER
OUTPUT DRIVER
I1 I2 I3 I4 VBIAS
REF
CSH
CSL
SLOPE COMPENSATION
Figure 4. Main PWM Comparator Functional Diagram
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet MAX1637.PDF ] | |
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