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PDF MAX8627 Data sheet ( Hoja de datos )
| Número de pieza | MAX8627 | |
| Descripción | Synchronous Boost Converter | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX8627 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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19-3995; Rev 0; 3/06
EVAALVUAAILTAIOBNLEKIT
Low VBATT, 20µA IQ, 1MHz Synchronous
Boost Converter with True Shutdown
General Description
The MAX8627 step-up converter is a high-efficiency,
low-quiescent current, synchronous boost converter
with True Shutdown™ and inrush current limiting. The
MAX8627 generates any boosted output voltage from
3V to 5V from either a 2-cell NiMH/NiCd or a single-cell
Li+/Li polymer battery.
Quiescent current is only 20µA (typ), and at light loads
the converter pulses only as needed for best efficiency.
At higher loads, PWM mode maintains fixed 1MHz
operation for lowest noise and ripple.
The MAX8627 includes an internal soft-start to limit
inrush current to a maximum of 500mA. Additional fea-
tures include True Shutdown, internal compensation,
and adjustable current limit. The MAX8627 is available
in a tiny 3mm x 3mm TDFN package and is ideal for
use in handheld devices such as DSCs, PDAs, and
smartphones.
Applications
DSC Motors and Backup Power
Microprocessor/DSP Core Power
Cellphones, PDAs, MP3 Players
Portable Handheld Devices
True Shutdown is a trademark of Maxim Integrated Products, Inc.
Typical Operating Circuit
INPUT BATTERY
2.5V TO 4.2V C1 C2
L1
ON
OFF
R4
4, 5
BATT
3
ON
8, 9
LX
6,7
POUT
12
MAX8627
AGND
OUTS
14
13 ILIM
2
FB
C3 C4
OUTPUT
3V TO 5V
UP TO 1A
R1
R3
1
GND
10, 11
PGND
R2
Features
♦ 1MHz PWM Switching Frequency
♦ True Shutdown Output
♦ Up to 95% Efficiency
♦ 1.0A Guaranteed Output Current
♦ Soft-Start Eliminates Inrush Current
♦ 20µA (typ) Quiescent Current
♦ 0.1µA Logic-Controlled Shutdown
♦ Internal Synchronous Rectifier
♦ Internal Compensation
♦ Adjustable Current Limit
♦ Low-Noise Antiringing Feature
♦ Tiny 14-Pin, 3mm x 3mm, TDFN Package
Ordering Information
PART
PIN-
PACKAGE
PKG
CODE
TOP
MARK
MAX8627ETD+ 14 TDFN-EP*
3mm x 3mm
T1433-2
AAQ
Note: The device operates in the -40°C to +85°C extended oper-
ating temperature range.
*EP = Exposed pad.
+Denotes lead-free package.
Pin Configuration
TOP VIEW
14 13 12 11 10 9 8
MAX8627ETD+
+
1234567
TDFN 3mm x 3mm
________________________________________________________________ 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  
Low VBATT, 20µA IQ, 1MHz Synchronous
Boost Converter with True Shutdown
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VOUTS = VPOUT = 5V, VON = VBATT = 3.6V, TA = +25°C, unless otherwise noted.)
SOFT-START TIME vs. INPUT VOLTAGE
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0.5 1.5 2.5 3.5 4.5 5.5
INPUT VOLTAGE (V)
PEAK INDUCTOR CURRENT vs. VILIM
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0.45
0.65 0.85 1.05
VILIM (V)
1.25
HEAVY LOAD SWITCHING WAVEFORMS
MAX8627 toc12
VPOUT
100mV/div
(AC-COUPLED)
2V/div
VLX
0
ILI 1A/div
1μs/div
0
LIGHT-LOAD SWITCHING WAVEFORMS
MAX8627 toc13
VPOUT
100mV/div
(AC-COUPLED)
2V/div
VLX
0
1A/div
ILI
0
40μs/div
LOAD TRANSIENT RESPONSE
MAX8627 toc14
VPOUT
100mV/div
(AC-COUPLED)
VBATT
LINE TRANSIENT RESPONSE
MAX8627 toc15
2V/div
0
ILOAD
20μs/div
500mA/div
0
VPOUT
100μs/div
100mV/div
(AC-COUPLED)
_______________________________________________________________________________________ 5
5 Page 
Low VBATT, 20µA IQ, 1MHz Synchronous
Boost Converter with True Shutdown
incremented by 230mA. If after 13 increments, the out-
put is still not in regulation, the MAX8627 latches off,
assuming a short-circuit overload condition exists on
the output. To clear the latched condition, cycle ON.
Fault Protection
The MAX8627 has a fault-overload protection. After
soft-start, the device is set to detect an out-of-regula-
tion state that could be caused by an overload. If the
output remains faulted for 65ms, then the MAX8627
latches off. Fault-detection circuitry is disabled during
soft-start. If short on the output exists before the
MAX8627 is turned ON, the converter completes the
soft-start sequence and latches off. The converter can
be reinitialized from a fault latch-off state by toggling
the ON pin or by cycling the input power.
BATT/Damping Switch
The MAX8627 features an internal damping switch to
minimize ringing at LX caused by the resonant circuit
formed by the inductor and output capacitor in discon-
tinuous conduction mode. This occurs at light loads.
The damping switch connects across the inductor
when the inductor energy is depleted and supplies a
path to dissipate the resonant energy. Damping LX
ringing does not change the output ripple but reduces
EMI.
Applications Information
Setting the Output Voltage
To set the output voltage to between 3V and 5V, con-
nect FB to the center of an external resistor voltage-
divider between OUTS and GND, as shown in Figure 1.
Select the value of R2 less than 500kΩ, and then calcu-
late the value for R1 as follows:
R1 =
R2
x
⎛
⎝⎜
VOUT
VFB
⎞
−1⎠⎟
where VFB is the FB regulation voltage, 1.015V (typ).
Inductor Selection
In most step-up converter designs, a reasonable inductor
value can be derived from the following equation,
which sets peak-to-peak inductor current at 1/2 the DC
inductor current:
L = 2 x VBATT x D x (1−D)
IOUT(MAX) x fSW
where fSW is the switching frequency (1MHz), and D is
the duty factor given by D = 1 - ( VBATT / VOUT ).
Using L from the equation above results in a peak-to-
peak inductor current ripple of 0.5 x IOUT / (1 - D), and
a peak inductor current of 1.25 x IOUT / (1 - D). Ensure
the peak (saturation) current rating of the inductor
meets or exceeds this requirement.
The recommended inductance range for the MAX8627 is
1µH to 4.7µH. See Table 1 for recommended inductors.
Capacitor Selection
Output Capacitor
Output capacitors C3 and C4 in Figure 1 are required to
keep the output voltage ripple small and to ensure regu-
lation loop stability. The output capacitors must have low
impedance at the switching frequency. Ceramic capaci-
tors are highly recommended due to their small size and
low ESR. Make sure the output capacitors maintain their
capacitance over DC bias and the desired operating
temperature range. Ceramic capacitors with X5R or X7R
temperature characteristics generally perform well. Two
22µF ceramic capacitors in parallel are recommended.
Alternatively, two 47µF tantalum capacitors with 70mΩ or
lower ESR may be used.
Input Capacitor
Input capacitors C1 and C2 reduce the current peaks
drawn from the battery or input power source and reduce
switching noise in the IC. The impedance of the input
capacitors at the switching frequency should be kept
very low. Ceramic capacitors are highly recommended
due to their small size and low ESR. Make sure the input
capacitors maintain their capacitance over DC bias and
the desired operating temperature range. Ceramic
capacitors with X5R or X7R temperature characteristics
generally perform well. Two 22µF ceramic capacitors are
recommended.
Table 1. Recommended Inductors
PART
TOKO A918CY
TOKO A997AS
INDUCTANCE (μH)
1.0
1.5
RATED CURRENT (mA)
3500
2150
SIZE:
L (mm, typ) x W (mm, typ) x H (mm, max)
6.3 x 6.2 x 2
3.8 x 3.8 x 1.8
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MAX8627.PDF ] | |
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