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參數資料
| 型號： | MAX624 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Dual-Output, 1MHz DC-DC Boost Converter for PCMCIA Applications(升壓型，輸出電壓5V/12V/可調,輸出電流200mA的DC-DC變換器) |
| 中文描述： | 雙輸出，1MHz的DC - DC升壓轉換器應用為PCMCIA（升壓型，輸出電壓5V/12V /可調，輸出電流200毫安的直流變換器） |
| 文件頁數： | 8/16頁 |
| 文件大?。?/td> | 215K |
| 代理商： | MAX624 |
______S tandard Applic ation Circ uit
In the standard application circuit (Figure 1), the
MAX624 generates 5V at 200mA (guaranteed) and 12V
at 80mA from a 3.3V or 5V input, and includes soft-start
and inrush surge-current limiting features. Successful
use of the circuit does not require calculations; use the
values given in Figure 1. For more detailed applications
information, see the Design Procedure for Main and
Auxiliary SMPS.
_______________Detailed Desc ription
The MAX624 is a dual-output DC-DC boost converter.
The device accepts input voltages from 3V to 5.5V
and generates two outputs: a 5V output at 200mA,
and an adjustable output (i.e. 12V or 30V). The main
5V output has an internal MOSFET switch and current-
sense resistor (0.15
), which senses the output cur-
rent and triggers the current-limit comparator. The
auxiliary SMPS’s current-limit resistor and MOSFET
switch are external to the device. The current-limit
voltage of the auxiliary SMPS is 200mV. Both the main
and auxiliary SMPS have a soft-start feature that
varies the start-up time of the outputs. The SS output
source impedance of the two outputs is 20k
to
charge the external SS capacitor to 150mV (5V out-
put) or 200mV (auxiliary output). The impedance of
the SS pin when the device is in reset (5V) and when
ONA = low (auxiliary) is 50
to GND. Full current limit
is reached at a 50μs/nF rate.
To prevent surge currents when the card is plugged into
a live socket, this device is capable of driving an external
high-side N-channel MOSFET in series with the main
V
CC
supply to the card. The EXT pin drives the gate of
the external MOSFET and is fed by an internal charge-
pump tripler that delivers three-times V
IN
, even in shut-
down mode. The output source impedance of EXT is
approximately 100k
, and has an active pull-down.
The SS capacitor and the external inrush-limiting MOS-
FET are optional components, not necessary unless
inrush current is a concern. However, do not remove C9.
When the MAX624 is in reset, the FB5 and VA outputs
are discharged to V
IN
via two internal switches (Figure
2). Discharging the output capacitors to a low voltage
level protects against false programming of flash mem-
ory chips.
5V Main S MPS
The main output is powered from the FB5 pin (i.e.,
bootstrapped) for higher speed and lower on-resis-
tance of the power MOSFET. This SMPS consists of an
error comparator, an output undervoltage-lockout com-
parator (set at 4V output), a timing generator for t
ON
and t
OFF
, a current-limit comparator, a MOSFET driver,
and the power switch (Figure 2).
The error comparator’s noninverting input voltage is
internally set to V
REF
. FB5’s voltage is scaled internally,
so that when it exceeds 5V the comparator output trips
and shuts down the PFM.
Leaving only the error comparator on when the switch
is off keeps the quiescent current low. The current com-
parator is powered up after the switch is turned on. This
provides leading-edge blanking on the current com-
parator, in order to filter noise spikes caused by switch
gate capacitance so they don’t trip the overcurrent
comparator and turn off the switch.
The main PFM has an undervoltage-lockout circuit that
trips at 4V (preset internal threshold). Until the 4V thresh-
old is reached, the timing generator is disabled and a
100kHz start-up oscillator is used to generate the output.
M
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applic ations
8
_______________________________________________________________________________________
MAX624
12
LX5
11
DA
AUXILIARY
OUTPUT
+12V
80mA
C2
4.7
μ
F
L2
5
μ
H
Q1
1/2 7101
C9
3300pF
L1
5
μ
H
D2*
C8
0.01
μ
F
C3
2.2
μ
F
C4
10pF
TOMICROCONTROLLER
*D1, D2: MOTOROLA
MBR0520L
C5 CAN BE REDUCED IN VALUE (0.1
μ
F) IF THE INPUT LEAD INDUCTANCE IS LOW.
NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS
AND SHOULD BE KEPT TOMINIMAL LENGTHS.
R1
0.22
+5V MAIN OUTPUT
200mA
V
IN
15
16
FB5
13
ONA
6
VIN
D1*
CSA
1
EXT
R5
500k
V
SWITCHED
R6
100k
SHDN
5
SS5
7
C7
0.1
μ
F
8
14
4
PGND
GND
SSA
C6
0.1
μ
F
2
3
REF
10
VA
9
FBA
ON/OFF
C5
4.7
μ
F
R2
10
1/2 7101
C1
4.7
μ
F
SHUTDOWN
RESET
Figure 1. Standard Application Circuit
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