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PDF MAX1844 Data sheet ( Hoja de datos )
| Número de pieza | MAX1844 | |
| Descripción | High-Speed Step-Down Controller | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-1993; Rev 3; 9/02
EVAALVUAAILTAIOBNLEKIT High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
General Description
The MAX1844 pulse-width modulation (PWM) controller
provides high efficiency, excellent transient response,
and high DC output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
CPU core or chipset/RAM supplies in notebook com-
puters.
www.DataSheeMt4aUx.cimom’s proprietary Quick-PWM™ quick-response,
constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides
100ns “instant-on” response to load transients while
maintaining a relatively constant switching frequency.
Efficiency is enhanced by an ability to drive very large
synchronous-rectifier MOSFETs. Accurate current sens-
ing to ensure reliable overload protection is available
using an external current-sense resistor in series with
the synchronous rectifier. Alternatively, the synchronous
rectifier itself can be used for less accurate current
sensing at the lowest possible power dissipation.
Single-stage buck conversion allows the MAX1844 to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the 5V system supply instead of the
battery) at a higher switching frequency allows the mini-
mum possible physical size.
The MAX1844 is intended for CPU core, chipset,
DRAM, or other low-voltage supplies as low as 1V. It is
available in 20-pin QSOP, and QFN packages and
includes both adjustable overvoltage and undervoltage
protection.
For a dual step-down PWM controller with accurate cur-
rent limit, refer to the MAX1845. The MAX1714/ MAX1715
single/dual PWM controllers are similar to the MAX1844/
MAX1845 but do not use current-sense resistors.
Notebook Computers
Applications
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V Supplies
*Contact factory for availability.
Quick-PWM is a trademark of Maxim Integrated Products.
Pin Configuration appears at end of data sheet.
Features
o Ultra-High Efficiency
o Accurate Current-Limit Option
o Quick-PWM with 100ns Load-Step Response
o 1% VOUT Accuracy Over Line and Load
o 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output
Range
o 2V to 28V Battery Input Range
o 200/300/450/600kHz Switching Frequency
o Adjustable Overvoltage Protection
o Adjustable Undervoltage Protection
o 1.7ms Digital Soft-Start
o Drives Large Synchronous-Rectifier FETs
o 2V ±1% Reference Output
o Power-Good Window Comparator
Ordering Information
PART
MAX1844EEP
MAX1844EGP*
MAX1844ETP
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
20 QSOP
20 QFN
20 Thin QFN
Minimal Operating Circuit
5V INPUT
BATTERY
4.5V TO 28V
VCC
SHDN
UVP
ILIM
VDD
V+
BST
DH
MAX1844
REF LX
DL
PGOOD CS
LATCH
OVP OUT
FB SKIP
GND
OUTPUT
2.5V
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, VCC = VDD = 5V, SKIP = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER
Minimum Off-Time
Quiescent Supply Current (VCC)
Quiescent Supply Current (VDD)
www.DataSheetQ4uUi.ecsocment Supply Current (V+)
Shutdown Supply Current (VCC)
Shutdown Supply Current (VDD)
Shutdown Supply Current (V+)
Reference Voltage
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
CONDITIONS
(Note 2)
FB forced above the regulation point
FB forced above the regulation point
Measured at V+
SHDN = GND
SHDN = GND
SHDN = GND, V+ = 28V, VCC = VDD = 0 or 5V
VCC = 4.5V to 5.5V, no external REF load
With respect to error comparator threshold, no load
OVP = GND, rising edge, hysteresis = 1%
MIN
1.98
12
TYP
MAX
500
800
5
40
5
5
5
2.02
17
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
PGOOD Trip Threshold (Lower)
External feedback, measured at FB with respect to
VOVP, 1V < VOVP 1.8V, rising edge, hysteresis = 1%
Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 1V < VOVP < 1.8V
With respect to error comparator threshold, no load
OUT falling edge, hysteresis = 1%
-30
-3.5
-12.5
+30
+3.5
-7.5
PGOOD Trip Threshold (Upper)
PGOOD Output Low Voltage
PGOOD Leakage Current
Current-Limit Threshold (Fixed)
Current-Limit Threshold
(Adjustable)
VCC Undervoltage
Lockout Threshold
Logic Input High Voltage
Logic Input Low Voltage
Logic Input Current
With respect to error comparator threshold, no load
OUT rising edge, hysteresis = 1%
ISINK = 1mA
High state, forced to 5.5V
GND - VCS, ILIM = VCC
GND - VCS, VILIM = 0.5V
GND - VCS, VILIM = 2V
Rising edge, hysteresis = 20mV,
PWM disabled below this level
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
LATCH, SHDN, SKIP
7.5
85
35
160
4.1
2.4
-1
12.5
0.4
1
115
65
240
4.4
0.8
1
UNITS
ns
µA
µA
µA
µA
µA
µA
V
%
mV
%
%
%
V
µA
mV
mV
V
V
V
µA
Note 1: When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error com-
parator threshold by 50% of the ripple. In discontinuous conduction (SKIP = GND, light load), the output voltage will have a
DC regulation level higher than the trip level by approximately 1.5% due to slope compensation.
Note 2: On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = GND, VBST = 5V,
and a 250pF capacitor connected from DH to LX. Actual in-circuit times may differ due to MOSFET switching speeds.
Note 3: Specifications to -40°C are guaranteed by design, not production tested.
Note 4: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the QFN
package. The MAX1844EEP, MAX1844EGP, and MAX1844ETP contain the same die and the QFN package imposes no
additional resistance in-circuit.
_______________________________________________________________________________________ 5
5 Page 
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
www.DataSheet4U.com
IN
2V TO 28V
V+
TON
SKIP
SHDN
OVP
ON-TIME FROM
COMPUTE OUT
TON
TRIG Q
1-SHOT
1.14V
REF
0.1V
TOFF
1-SHOT
Q TRIG
SQ
R
ERROR
AMP
S
Q
R
MAX1844
5V
BST
DH
LX
VDD +5V
DL
OUTPUT
LATCH
VCC - 1V
POR
20ms
0.1V TIMER
OVP/UVP
LATCH
VCC - 1V 0.7V
UVP
PGOOD
REF
-10%
REF
+10%
R 9R
CURRENT
LIMIT
Σ
ZERO CROSSING
x2
FEEDBACK
MUX
(SEE FIGURE 6)
ILIM
VCC - 1V
1.0V CS
GND
CHIP
SUPPLY
OUT
VCC
2V REF
REF
5V
FB
Figure 2. MAX1844 Functional Diagram
battery supply, the enable signal (SHDN) must be
delayed until the battery voltage is present in order to
ensure startup. The 5V bias supply provides VCC and
gate-drive power, so the maximum current drawn is:
IBIAS = ICC + f (QG1 + QG2) = 5mA to 30mA (typ)
where ICC is 550µA (typ), f is the switching frequency,
and QG1 and QG2 are the MOSFET data sheet total
gate-charge specification limits at VGS = 5V.
Free-Running, Constant-On-Time PWM
Controller with Input Feed-Forward
The Quick-PWM control architecture is a pseudo-fixed-fre-
quency, constant-on-time on-demand PWM with voltage
feed-forward (Figure 2). This architecture relies on the out-
put filter capacitor’s ESR to act as a current-sense resistor,
so the output ripple voltage provides the PWM ramp sig-
nal. The control algorithm is simple: the high-side switch
on-time is determined solely by a one-shot whose pulse
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet MAX1844.PDF ] | |
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