_______________General Description
The MAX624 is a dual DC-DC converter intended for
size-constrained applications, such as power supplies
that must fit inside PCMCIA memory cards. At the heart
of the MAX624 are two boost-topology converters, plus
auxiliary functions including a start-up inrush surge-cur-
rent limiter and a power-on reset output with timer
(power-good signal). The MAX624 accepts input volt-
ages from 3V to 5.5V and generates two outputs: a
fixed 5V ±4% output at 200mA (guaranteed), and an
adjustable auxiliary output that is configurable for vari-
ous loads with an external power transistor. The auxil-
iary output is typically set to 12V ±2% for flash memory
applications, but can be adjusted via a resistor divider
from VIN to 30V or more.
The MAX624’s high switching frequency (1MHz)
reduces external component sizes. High-frequency
switching losses have minimal impact on efficiency,
which is 85% for the main 5V supply. Small ceramic fil-
ter capacitors, together with the soft-start function,
reduce start-up inrush current surges.
________________________Applications
PCMCIA Memory Cards
Solid-State Disk Drives
Host-Side PCMCIA Adapters
LCD Bias Power Supplies
____________________________Features
♦1MHz Switching Frequency for Small
Components
♦5V ±4% Boost Converter with Internal Power
Switch
♦Adjustable ±2% Output Boost Converter with
External Power Switch
♦Optional Inrush Surge-Current Limiting
♦40µA Shutdown Current
♦0.5mA Quiescent Current
♦3.0V to 5.5V Input Range
♦85% Main 5V SMPS Efficiency
♦Independent Soft-Start for Each Supply
♦Reset Output with 2.8V ±3% Threshold and
4ms Timeout
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
________________________________________________________________
Maxim Integrated Products
1
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
VIN
LX5
PGND
FB5
GND
REF
RESET
EXT
TOP VIEW
MAX624
DA
CSA
VA
FBA
SSA
SS5
ONA
SHDN
SO
__________________Pin Configuration
MAX624
LX5 DA
AUXILIARY
OUTPUT
12V
80mA
(AS SHOWN)
4.7µF
5µH
N
4.7µF
2.2µF
0.22Ω
MAIN
OUTPUT
5V
200mA
INPUT 3V TO 5.5V
FB5
AUX. ON/OFF
SHUTDOWN
EXT
VIN
CSA
VA
FBA
500k
100k
5µH
0.1µF3300pF
GND
REF
ONA
SHDN
10pF
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0382; Rev 1; 8/95
PART
MAX624C/D
MAX624ISE -25°C to +85°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
Dice*
16 Narrow SO
______________Ordering Information
* Dice are tested at T
A
= +25°C. Contact factory for dice
specifications.
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = 3V, GND = PGND = 0V, SHDN = VIN, EXT open, FBA feedback resistors set for 12V, TA= TMIN to TMAX, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VIN, FB5, LX5, SHDN, ONA to GND...........................-0.3V to 7V
EXT to GND...............................................................-0.3V to 12V
RESET, REF to GND....................................-0.3V to (VIN + 0.3V)
PGND to GND.....................................................................±0.3V
SS5, SSA, DA, CSA, FBA to GND...............-0.3V to (FB5 + 0.3V)
VA to GND ................................................................-0.3V to 17V
Continuous Power Dissipation (TA= +70°C)
SO (derate 8.70mW/°C above +70°C).........................696mW
Operating Temperature Range
MAX624ISE......................................................-25°C to +85°C
Lead Temperature (soldering, 10sec).............................+300°C
ONA input will be inhibited until FB5 rises above this level
3V < VIN < 5.5V (Note 1)
Circuit of Figure 1, ILOAD = 100mA
3V < VIN < 5V, FB5 = 5V (Note 2)
3V < VIN < 5V, tON5 = K5 / VIN
VA = 12V, FBA = 2.1V
VA = 12V, VIN = 3V, ONA = 0V,
internal VIN to VA discharge switch
LX5 = 7V
FB5 = 5V, VIN = 3V, SHDN = 0V,
internal VIN to FB5 discharge switch
FB5 = 5.5V, VA = 12.5V
VIN = 5.5V, SHDN = ONA = 0V
3V < VIN < 5.5V (Note 1)
FB5 = 5.5V, SHDN = 3V, ONA = 0V
CONDITIONS
mV180 220CSA Current-Limit Threshold µA10CSA Bias Current V3.5 4.0 4.5Enable Trip Voltage Level %0.03 0.2Line Regulation
%85Efficiency 0.2 0.8Switch Off-Time Ratio (SR5) µs-V0.8 1.3 1.7Switch On-Time Constant (K5) A0.7 0.9 1.1Switch Current Limit µA10Switch Leakage Current Ω0.33 0.6Switch On-Resistance %0.03 0.2Line Regulation
V4.80 5.205V Output Voltage
V3.0 5.5Input Supply Range
nA100FBA Leakage Current
µA515VA Shutdown Discharge Current
µA100 5000FB5 Shutdown Discharge Current
µA30 60VA Quiescent Current
V1.96 2.04FBA Regulation Point
µA40 60VIN Shutdown Current
µA200 400FB5 Quiescent Current
UNITSMIN TYP MAXPARAMETER
Circuit of Figure 1, VIN = 3.3V, ONA = 0V µA500VIN Quiescent Current
Circuit of Figure 1, ILOAD = 60mA
3V < VIN < 5V, 7V < FBA < 11V (Note 3)
3V < VIN < 5V, tONA = KA / VIN
DA = 2.5V
FB5 = 5.5V
%75Efficiency 0.2 0.9Switch Off-Time Ratio (SRA) µs-V1.5 2.2 3.0Switch On-Time Constant (KA) A0.5DA Drive Current Ω415DA On-Resistance
OUTPUT VOLTAGES
SUPPLY CURRENTS
5V MAIN SMPS
AUXILIARY SMPS CONTROLLER
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
_______________________________________________________________________________________ 3
Note 1: Line Regulation is tested by measuring the reference line regulation, since both converters are supplied from the regulated
5V output.
Note 2: Switch off-time ratio guarantees that the inductor will go into continuous conduction. The ratio is tested for two cases for the
main SMPS:
1) VIN = 5V, FB5 = 5V SR5 = 0.120 x tOFF / tON
2) VIN = 3V, FB5 = 5V SR5 = 0.867 x tOFF / tON
Note that the constants are calculated from: (FB5 + 0.6V - VIN) / VIN
Note 3: Switch off-time ratio guarantees that the inductor will go into continuous conduction. The ratio is tested for two cases for the
auxiliary SMPS:
1) VIN = 5V, VA = 7V SRA = 0.520 x tOFF / tON
2) VIN = 3V, VA = 11V SRA = 2.867 x tOFF / tON
Note that the constants are calculated from: (VA + 0.6V - VIN) / VIN
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3V, GND = PGND = 0V, SHDN = VIN, EXT open, FBA feedback resistors set for 12V, TA= TMIN to TMAX, unless otherwise noted.)
SS5, SSA; SHDN = ONA = 3V
Rising VIN edge, typical hysteresis = 1%
VIN = 2V, ISINK = 0.1mA
VIN = 5.5V, ISOURCE = 0µA
RESET, ISINK = 2mA, VIN = 2.6V
SS5, SSA; SHDN = ONA = 0V
SHDN, ONA
VIN = 2.9V, ISOURCE = 2µA
SHDN, ONA
CONDITIONS
SHDN, ONA V2Input High Voltage
V1EXT Output Voltage in Reset 11.8 V
6.5
EXT Output Voltage
ms210RESET Timeout
kΩ14 20 28Source Resistance
V2.7 2.9RESET Trip Level
V0.4Output Low Voltage
Ω50 300Discharge Resistance
V0.8Input Low Voltage
µA±1Input Leakage
UNITSMIN TYP MAXPARAMETER
RESET, ISINK = 1mA, VIN = 3V VVIN - 0.8Output High Voltage
SOFT-START CONTROL
LOGIC INPUTS AND OUTPUTS
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
4 _______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
8
0-40 -20 20 40 100
RESET DELAY vs.
TEMPERATURE
2
1
6
7
MAX624-01
TEMPERATURE (°C)
RESET DELAY (ms)
06080
5
4
3
V
IN = 5V
VIN = 3.3V
1400
0-40 -20 20 40 100
QUIESCENT INPUT CURRENT vs.
TEMPERATURE
400
200
1000
1200
MAX624-02
TEMPERATURE (°C)
QUIESCENT INPUT CURRENT (µA)
06080
800
600
12V AUXILIARY SMPS
ONA = HIGH
SHDN = HIGH
5V MAIN SMPS
ONA = LOW
SHDN = HIGH
90
20 0.1m 1m 10m 100m 1
EFFICIENCY vs. LOAD CURRENT
(12V AUXILIARY SMPS)
40
30
MAX624-03
LOAD CURRENT (A)
EFFICIENCY (%)
50
70
60
80 VIN = 5V
VIN = 3.3V
100
00.1m 1m 10m 100m 1
EFFICIENCY vs. LOAD CURRENT
(5V MAIN SMPS)
30
20
10
MAX624-04
LOAD CURRENT (A)
EFFICIENCY (%)
40
80
70
60
50
90 VIN = 5V
VIN = 3.3V
ONA = LOW
10,000
1
10
1 1000
SWITCHING FREQUENCY vs.
LOAD CURRENT
100
1000
MAX624-07
LOAD CURRENT (mA)
SWITCHING FREQUENCY (kHz)
10 100
5V MAIN SMPS
VIN = 3.3V
001 34
QUIESCENT INPUT CURRENT vs.
INPUT VOLTAGE (12V AUXILIARY SMPS)
400
200
1200
1400
MAX624-05
INPUT VOLTAGE (V)
QUIESCENT INPUT CURRENT (µA)
256
1000
800
600
ONA = HIGH
SHDN = HIGH
001 34
QUIESCENT INPUT CURRENT vs.
INPUT VOLTAGE (5V MAIN SMPS)
200
100
600
700
MAX624-06
INPUT VOLTAGE (V)
QUIESCENT INPUT CURRENT (µA)
256
500
400
300
SHDN = HIGH
ONA = LOW
2.5
00 400 1000
LOAD REGULATION vs. LOAD CURRENT
(5V MAIN SMPS)
1.0
0.5
2.0
MAX624-08
LOAD CURRENT (mA)
LOAD REGULATION (%)
200 600 800
1.5
VIN = 3.3V
VIN = 5V
1.0
00 160
LOAD REGULATION vs. LOAD CURRENT
(12V AUXILIARY SMPS)
0.4
0.3
0.2
0.1
0.9
0.8
0.7
MAX624-09
LOAD CURRENT (mA)
LOAD REGULATION (%)
20 40 60 80 100 120 140
0.6
0.5 VIN = 3.3V
VIN = 5V
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
_______________________________________________________________________________________
5
50
001 3 6
SHUTDOWN CURRENT vs.
INPUT VOLTAGE
10
5
30
35
40
45
MAX624-10
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
245
25
20
15
TA = -25°C
TA = +85°C
TA = +25°C
800
03.0 3.2 3.4 4.0 4.2 5.0
LOAD CURRENT CAPABILITY
vs. INPUT VOLTAGE
200
100
500
600
700
MAX624-11
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
3.6 3.8 4.4 4.6 4.8
400
300
5V MAIN SMPS
12V AUXILIARY SMPS
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
A: ONA (5V/div) C: IIN (200mA/div)
B: 12V AUXILIARY SMPS D: VSWITCHED
(5V/div) (100mV/div, AC-COUPLED)
START-UP WAVEFORMS (12V AUXILIARY SMPS)
(VIN = 3.3V, ILOAD = 1.2mA, SHDN = HIGH)
B
A
C
D
100µs/div A: SHDN (5V/div) C: IIN (200mA/div)
B: 5V MAIN SMPS (1V/div) D: VSWITCHED (100mV/div,
AC-COUPLED)
START-UP WAVEFORMS (5V MAIN SMPS)
(VIN = 3.3V, ILOAD = 0A, ONA = LOW)
B
A
C
D
100µs/div
A: VIN (5V/div) C: RESET (5V/div)
B: VSWITCHED (5V/div) D: IIN (50mA/div)
START-UP INRUSH CURRENT (VIN = 3.3V)
(ILOAD = 5mA, SHDN = ONA = LOW)
B
A
C
D
1ms/div A: VIN (5V/div) C: RESET (5V/div)
B: VSWITCHED (5V/div) D: IIN (50mA/div)
START-UP INRUSH CURRENT (VIN = 5V)
(ILOAD = 5mA, SHDN = ONA = LOW)
B
A
C
D
1ms/div
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
6 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
A: ILOAD = 0mA to 80mA
B: 12V AUXILIARY SMPS (200mV/div, AC-COUPLED)
LOAD-TRANSIENT RESPONSE (12V AUXILIARY SMPS)
A
B
200µs/div A: ILOAD = 0mA to 200mA
B: 5V MAIN SMPS (50mV/div, AC-COUPLED)
LOAD-TRANSIENT RESPONSE (5V MAIN SMPS)
A
B
200µs/div
ILOAD = 20mA
A: VIN = 3.3V to 5V
B: 12V AUXILIARY OUTPUT (200mV/div, AC-COUPLED)
LINE-TRANSIENT RESPONSE
(12V AUXILIARY SMPS)
A
B
100µs/div
ILOAD = 40mA
A: VIN = 3.3V to 5V
B: 5V MAIN OUTPUT (50mV/div, AC-COUPLED)
LINE-TRANSIENT RESPONSE
(5V MAIN SMPS)
A
B
100µs/div
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
_______________________________________________________________________________________ 7
______________________________________________________________Pin Description
NAME FUNCTION
1EXT Gate-Drive Output. Drives inrush surge-current limiting MOSFET. EXT is fed by an internal charge-pump tripler
that swings from GND to VIN x 3.
2 RESET Power-On Reset Output. Low when VIN < 2.8V and for 4ms after VIN > 2.8V. EXT is low when RESET is low.
Swings from GND to VIN.
PIN
3 REF 2V Reference Output. Bypass to GND with 0.1µF. No external load current is allowed.
4 GND Quiet Analog Ground and Low-Side Current-Sense Input for Auxiliary SMPS
8 SSA Soft-Start Input for Auxiliary SMPS. An external soft-start capacitor varies the auxiliary SMPS start-up time. Ramp
time to full current limit is approximately 50µs per nF of soft-start capacitance.
7 SS5 Soft-Start Input for 5V Main SMPS. An external soft-start capacitor varies the 5V start-up time. Ramp time to full
current limit is approximately 50µs per nF of soft-start capacitance.
6 ONA On/Off Control Input for Auxiliary SMPS, low = off
5 SHDN Shutdown. Disables both SMPSs when low. In shutdown, the surge-protection input MOSFET is kept on.
13 FB5 Feedback Input for 5V Main SMPS. FB5 also serves as the supply voltage rail for much of the internal circuitry
for both SMPSs (bootstrap supply input).
12 DA Gate-Drive Output for Auxiliary SMPS. Swings 0V to FB5.
11 CSA Current-Sense Input for Auxiliary SMPS. Current-limit threshold is 200mV nominal with respect to GND.
10 VA Output Voltage Sense Input for Auxiliary SMPS. The only purpose of this pin is to set the SMPS timing algorithm.
Internally, VA connects to the top of a 250kΩ±30% resistor that connects to VIN.
9 FBA Feedback Input for Auxiliary SMPS. Regulates around REF (2V nominal). FBA is a high-impedance CMOS input.
16 VIN Input Supply Voltage from the External Supply. Normal operating range is 3V to 5.5V.
15 LX5 Drain Connection for 5V Main SMPS Power MOSFET
14 PGND Power Ground, source connection for the main 5V SMPS power MOSFET
______Standard Application Circuit
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 Description
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 (0.15Ω), 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 20kΩto
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 50Ωto 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
VCC 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 VIN, even in shut-
down mode. The output source impedance of EXT is
approximately 100kΩ, 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 VIN 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 SMPS
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 tON
and tOFF, a current-limit comparator, a MOSFET driver,
and the power switch (Figure 2).
The error comparator’s noninverting input voltage is
internally set to VREF. 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.
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
8 _______________________________________________________________________________________
MAX624
12
LX5
11
DA
AUXILIARY
OUTPUT
+12V
80mA
C2
4.7µF
L2
5µH
Q1
1/2 7101
C9
3300pF
L1
5µHD2*
C8
0.01µF
C3
2.2µF
C4
10pF
TO MICROCONTROLLER
*D1, D2: MOTOROLA
MBR0520L
C5 CAN BE REDUCED IN VALUE (0.1µF) IF THE INPUT LEAD INDUCTANCE IS LOW.
NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS
AND SHOULD BE KEPT TO MINIMAL LENGTHS.
R1
0.22Ω
+5V MAIN OUTPUT
200mA
VIN
15
16
FB5
13
ONA
6
VIN
D1*
CSA
1
EXT
R5
500k
VSWITCHED
R6
100k
SHDN
5
SS5
7
C7
0.1µF
8
144 PGNDGND
SSA
C6
0.1µF
3
REF
10
VA 9
FBA
ON/OFF
C5
4.7µF
R2
10Ω
1/2 7101
C1
4.7
µ
F
SHUTDOWN
2
RESET
Figure 1. Standard Application Circuit
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
_______________________________________________________________________________________ 9
Table 1. Recommended Components for 12V/80mA Auxiliary SMPS and 5V Main SMPS
DESIGNATION QTY DESCRIPTION SOURCE/TYPE
Q1 1 Dual, N-channel MOSFET IRF7101 or Si9956DY
L1, L2 2 5µH inductors Sumida CLS-62B, drawing #94T-217
C3 1 2.2µF ceramic capacitor Marcon THCR30E1E225ZT or THCS30E1E225ZT
C4 1 10pF capacitor
C5, C6, C7 3 0.1µF capacitors Murata-Erie GRM42-6X7R104K025V
C8 1 10nF capacitor
C9 1 3300pF capacitor
D1, D2 2 IF= 1A, VR= 20V Schottky rectifier Motorola MBR0520L
R1 1 0.22Ω±10% resistor Ohmtek 1205LR220LBT or IMS RC-I-1206
R2 1 10Ωresistor
C1, C2 2 4.7µF ceramic capacitors Marcon THCR40E1E475ZT or THCS40E1E475ZT
Table 2. Component Suppliers
SUPPLIER PHONE FAX
IMS (401) 683-9700 (401) 683-5571
International Rectifier (310) 241-7876 (310) 640-6515
Motorola (602) 244-3576 (602) 244-4015
Murata-Erie (800) 831-9172 (814) 238-0490
Ohmtek (716) 283-4025 (716) 283-5932
Siliconix (408) 988-8000 (408) 970-3950
Sumida USA (708) 956-0666 (708) 956-0702
Sumida Japan (03) 607-5111 (03) 607-5144
Toshiba Marcon (708) 913-9980 (708) 913-1150
* When off, VAUX = VIN.
** VAUX is set to 12V in this example.
Table 3. Operating States
STATE VIN SHDN ONA VMAIN VAUX* EXT I (VIN)
Reset <2.8V X X OFF OFF OFF 10µA
Shutdown >2.8V LO X OFF OFF ON 40µA
Main On >2.8V HI LO 5.0V OFF ON 0.52mA
Both On >2.8V HI HI 5.0V 12V** ON 1.2mA
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
10 ______________________________________________________________________________________
MAX624
ENBL
11V
2V
150k
P
100k QQ
IC POWER
PFM LOGIC
R
D
S
FB5
LX
PGND
EXT
2.8V
VIN
REF
RESET
VIN OUT
VOLTAGE
TRIPLER
CHARGE
PUMP
2.0V
REFERENCE
R
QD
5ms
DELAY
SHDN
ONA
GND
FB5
4V
CURRENT
LIMIT
ENBL
tON = K5/VIN
tOFF = –––––––––––––
K5
2(VFB5 + 0.6V - VIN)
N
0.2Ω
0.15Ω
SS5
2V
P
N
20k250k
Q
2V PFM LOGIC
R
D
S
FBA
VA
CSA
SSA
DA
N
PGND
FB5
CURRENT
LIMIT
ENBL
tON = KA/VIN
tOFF = ––––––––––––
KA
2(VA + 0.6V - VIN)
2V
20k180k
Figure 2. Functional Block Diagram
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
______________________________________________________________________________________ 11
Adjustable Auxiliary SMPS
The auxiliary output is adjustable from 5V to 15V; two
external resistors set the output voltage. The auxiliary
SMPS is similar to the main SMPS, but it does not have
an undervoltage-lockout comparator, and requires an
external power MOSFET (see
Typical Operating Circuit
and
Design Procedure for Main and Auxiliary SMPS
).
The 5V SMPS undervoltage-lockout circuit overrides the
ONA input until the 5V main SMPS (VMAIN) output reach-
es about 4V. This feature ensures that the external auxil-
iary SMPS MOSFET has sufficient gate-drive voltage.
The adjustable output voltage can be increased to 30V
or higher (Figure 9). However, such high output volt-
ages cause the inductor current to become discontinu-
ous, consequently reducing the load-current capability.
Voltage Reference
The MAX624’s internal 2.00V reference is powered from
the VIN input. The reference is kept alive in all modes
(needed for reset function) and must be bypassed with
a 0.1µF capacitor to GND for low-noise operation. No
external load current is allowed.
Pulse-Frequency-Modulation
Control Scheme
A unique pulse-frequency-modulation (PFM) control
scheme, with adjustable on-time/off-time circuitry and
current limit, is a key feature of both the main SMPS regu-
lator and the auxiliary SMPS converter. The PFM scheme
combines the advantages of pulse-width modulation
(high output power and efficiency) with those of a tradi-
tional pulse-skipper (ultra-low quiescent currents). The
on-time is calculated from the input voltage, and the off-
time is calculated from VOUT - VIN. The off-time is divided
by two so that the inductor current can ramp into continu-
ous conduction. Switch on-times are adjusted down at
high input voltages in order to minimize output ripple.
Use the following formulas to calculate tON and tOFF:
tON = K / VIN
tOFF = 0.5 x K / (VOUT + 0.6V - VIN)
Nominally, K = 1.3µs-V for the main SMPS, and K =
2.2µs-V for the auxiliary SMPS. The K (design constant)
scale factor that sets the switching frequency also sets
the peak inductor current to control no-load output rip-
ple at low input-to-output differentials (e.g., VIN = 5V,
VOUT = 5V).
The PFM’s high switching frequency (1MHz) helps
reduce external component size. When the peak current
limit is reached, the MOSFET switch turns off for at least
the off-time set by the one-shot. When the comparator
monitoring the output voltage is less than the desired
value, it starts another cycle by turning the switch on.
Surge Prevention
Surge prevention is accomplished by slowly high-side
driving an N-channel switch. The gate is driven by an
on-chip charge pump that triples the input voltage. This
charge pump is powered from the input voltage and
runs continuously. The reset trip voltage is set to 2.8V to
guarantee that the surge-prevention MOSFET can be
turned on under worst-case low input voltage condi-
tions. Otherwise, the card would go out of reset even
though the supply voltage is unavailable.
Design Procedure for
__________Main and Auxiliary SMPS
Output Filter Capacitor Selection
The output filter capacitor should have the minimum pos-
sible ESR for low ripple, and the minimum possible value
for smallest physical size (i.e., ceramic). Larger sizes can
be used for lower cost (i.e., tantalum). The output ripple
is the sum of two components, due to CFand ESR.
To select the filter capacitor value, follow the steps below:
1) Select the maximum ripple you can tolerate (e.g.,
80mV).
2) Calculate the value of CF, using the formula below:
2 x K x ILOAD
CF(in F) > —————————————
VRIPPLEC (VOUT + 0.5V - VIN)
where K is a design constant. Use the worst-case
value from the
Electrical Characteristics
.
3) Calculate the output capacitor’s required ESR, using
the formula below.
VRIPPLEESR x VIN
ESR (in Ω) < —————————————
4 x ILOAD (VOUT + 0.5V - VIN)
For example: For the 5V main SMPS with K = 1.7µs-V,
ILOAD = 200mA, VOUT = 5V, VIN = 3.3V, and maximum
tolerable ripple = 80mVp-p, assume VRIPPLEC = 60mV
and VRIPPLEESR = 20mV. Calculate CF> 5µF with ESR
< 37mΩ.
Inductor Selection
Select the inductor value to optimize one of the following:
• High Load Currents: Higher inductor values give higher
load currents, since the inductor operates in deep con-
tinuous conduction.
• Small Physical Size: Lower inductor values result in
lower energy storage requirements, hence smaller
physical size. The filter capacitor can also be smaller,
since the inductor current can ramp up faster when the
load is suddenly increased.
MAX624
To select the inductor value for the main SMPS, take
the following steps:
1) Select the input voltage.
2) Select ILIMIT and ILOAD.
3) Use the specified data sheet values and the following
formula: SR5 x K5 (VIN - A)
L (in H) = ———————————————
2 x ILIMIT (VIN + A) - 2 x ILOAD x B
A = ILIMIT x RON
B = VOUT + VDIODE
where: inductor current = ILIMIT(min) = 0.7A,
ILOAD(min) = 200mA, SR5 (the switch off-time ratio) =
0.8, K5(max) = 1.7µs-V, RON(max) = 0.6Ω, VOUT =
5V, VDIODE = 0.5V, VIN(min) = 3.0V, and L = 5µH (for
best performance, use a Sumida 5µH (CLS-62B)).
Input Filter Capacitor Selection
The input filter capacitor is required to reduce reflected
current ripple to the input source, and to improve effi-
ciency by providing a low-impedance path for the rip-
ple current. For memory card applications, the input
filter capacitor is absolutely necessary due to possible
contact resistance in the edge connector. To limit surge
currents, use smaller values. Ceramic capacitors are
the best choice.
Output Voltage and Component
Selection for the Auxiliary SMPS
To select the output voltage and component values for
the auxiliary SMPS, take the following steps:
1) Select the desired output voltage between 5V and
15V (e.g., 12V).
2) Select the minimum input voltage (VIN).
3) Select R6 and R5. Choose R6 in the 10kΩto 200kΩ
range (e.g., 100kΩ). Choose R5 = R6 (VOUT / VREF -
1). For example, if VOUT = 12V, then R6 = 100kΩand
R5 = 500kΩ.
4) Select the desired output current (IOUT). Calculate
the minimum inductor current (ILIMIT) using the fol-
lowing formula:
ILIMIT (in Amps) = [(VOUT + 0.5V) / (VIN(min) - 0.3V)]
x ILOAD x 2
For example: VOUT = 12V, VIN(min) = 3V,ILOAD =
80mA, and ILIMIT = 0.7A.
5) To calculate the minimum required inductor value,
use the following formula:
SRA x KA (VIN - A)
L (in H) = ——————————————
2 x ILIMIT (VIN - A) - 2 x ILOAD x B
A = ILIMIT x RON
B = VOUT + VDIODE
For example: ILOAD = 80mA, ILIMIT = 0.7A (calculat-
ed using the above formula), SRA (switch off-time
ratio) = 0.9, KA (switch on-time) = 3.0µs-V,
RON(max) = 0.2Ω, VOUT = 12V, VDIODE = 0.5V, and
L(min) = 3.8µH.
6) R (in Ω) = 180mV / ILIMIT = 0.25Ωfor ILIMIT = 0.7A.
7) To select the output capacitor value, take the follow-
ing steps:
A) Select the maximum ripple you can tolerate.
B) Calculate CFusing the formula below.
2 x KA x ILOAD
CF(in F) = ——————————————
VRIPPLEC x (VOUT + 0.5 - VIN)
C) Calculate the output capacitor’s required ESR
using the formula below.
VRIPPLEESR x VIN
ESR (in Ω) = ——————————————
4 x ILOAD x (VOUT + 0.5V - VIN)
___PC Board Layout and Grounding
Because of the MAX624’s high-frequency operation,
careful PC board layout is necessary to minimize
ground bounce and noise. PC board layout instructions
should be explicit, and the layout artist should work
from a pencil sketch that shows the placement of
power switching components and high-current routing.
Use Figures 3–8 (the component placement guide and
PC board layouts for the MAX624 evaluation board) as
a rough guide for component placement and ground
connections. A ground plane is essential for optimum
performance. In most applications, the circuit will be
located on a multilayer board, and full use of the four or
more copper layers is recommended. Use the following
step-by-step guide.
1) Place the high-power components (C1, C2, C3, D1,
D2, L1, L2, Q1, and R1) first.
Priority 1: Minimize current-sense resistor trace
lengths.
Priority 2: Minimize ground trace lengths in the high-
current paths (the bold lines in the appli-
cation circuits).
Priority 3: Minimize other trace lengths in the high-cur -
rent paths. Use traces more than 5mm wide.
Ideally, surface-mount power components are
butted up against one another with their ground ter-
minals almost touching. These high-current grounds
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
12 ______________________________________________________________________________________
(C1, C2, C3, R1, and PGND) are then connected
with a wide filled zone of top-layer copper, so they
don’t go through vias. The resulting top-layer “sub-
ground plane” is connected to the normal inner-layer
ground plane at the ground output terminals (at the
ground of C2). Other high-current paths should also
be minimized, but focusing on short ground and cur-
rent-sense connections eliminates about 90% of all
PC board layout problems. See Figures 3–8 for
examples.
2) Place the IC and signal components. Keep the main
switching node traces (LX node) short and away
from sensitive analog components (current-sense
traces and REF and SS capacitors). Important: the
IC must be no farther than 5mm from the current-
sense resistor. Keep the gate-drive trace shorter
than 10mm and route it away from REF and SS.
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
______________________________________________________________________________________ 13
Figure 3. MAX624 PC Board Component Placement Guide
Figure 6. MAX624 PC Board Layout—V
SWITCHED
Plane
Figure 5. MAX624 PC Board Layout—Component Side
Figure 4. MAX624 PC Board Drill and Mechanical Guide
MAX624
________________Application Circuits
Positive 30V Auxiliary Output Circuits
The MAX624 can be used to generate a 30V output at
25mA (Figures 9 and 10). Note that the 12V zener clamp
shown in Figure 10 must be used for 5V input applica-
tions. A 30V output at 25mA can be generated by tying
the VA pin to the main SMPS output, but this circuit does
not make optimal use of the inductor (the off-time is
about 0.5µs). An alternative approach is to clamp the VA
output to 12V using a zener. The off-time is optimized
(reduced), which in turn makes better use of the inductor
and produces a higher output current of about 35mA
(Figure 10). Note that the 12V zener clamp shown in
Figure 10 must be used for 5V input applications.
Negative Output Application Circuit
The MAX624 can be used to generate a negative 30V
output to power-up LCD supplies (Figure 11). This cir-
cuit is part switching regulator and part charge pump.
The switching regulator boosts the input to a high posi-
tive voltage (30V), while the actual negative voltage is
generated using a charge-pump tap on the switching
node. The negative 30V output has a 5% load-regula-
tion error from 1mA to 20mA. The ratio of R5 and R6
resistors can be used to adjust the LCD contrast.
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
14 ______________________________________________________________________________________
Figure 7. MAX624 PC Board Layout—Ground Plane Figure 8. MAX624 PC Board Layout—Solder Side
MAX624
12
LX5
11
DA
AUXILIARY OUTPUT
+30V
25mA
VIN
3.3V ONLY
C2
L2
L1
D2
C8
C3
0.47µF
10pF
L2: 2.2µH, MURATA-ERIE
LQH3C2R2MO400
C3: 4.7µF, MARCON
THCR30E1H474ZT
D2: MOTOROLA MBR0540
R1
0.22Ω
+5V MAIN OUTPUT
200mA 15
16
FB5
13
ONA
6
VIN
D1
CSA
10 VA
9
FBA
R5
500k
R6
36k
EXT
1
3300pF
SS5
7
C7
8
144 PGNDGND
SSA
C6
3
REF
ON/OFF
4.7µF
NOTE: USE FOR VIN = 3.3V ONLY
NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS
AND SHOULD BE KEPT TO MINIMAL LENGTHS.
Figure 9. Positive 30V (25mA) Auxiliary Output Application
Circuit
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
______________________________________________________________________________________ 15
MAX624
12
LX5
11
DA
AUXILIARY OUTPUT
+30V
35mA
VIN
C2
L2
L1
D2
C8
C3
10pF
L2: 2.2µH, MURATA-ERIE LQH3C2R2MO400
C3: 0.47µF, MARCON THCR30E1H474ZT
D2: MOTOROLA MBR0540
NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS
AND SHOULD BE KEPT TO MINIMAL LENGTHS.
R1
0.22Ω
+5V MAIN OUTPUT
200mA 15
16
FB5
13
ONA
6
VIN
D1
CSA
10
VA
9
FBA
R5
500k
100k
12V
R6
36k
EXT
1
3300pF
SS5
7
C7
8
144 PGNDGND
SSA
C6
3
REF
ON/OFF
4.7µF
Figure 10. Positive 30V (35mA) Auxiliary Output Application
Circuit
MAX624
12
LX5
11
DA
AUXILIARY OUTPUT
-30V
25mA
VIN
C2
L2
L1
D2
D4
D3
C8
C3
0.1
µF
10pF
L2: 2.2µH, MURATA-ERIE LQH3C2R2MO400
C14, C15: CERAMIC (50V)
D2: 1N4148
D3, D4: MOTOROLA MBR0540
NOTE: BOLD LINES DESIGNATE HIGH-CURRENT PATHS
AND SHOULD BE KEPT TO MINIMAL LENGTHS.
R1
0.22Ω
+5V MAIN OUTPUT
200mA 15
16
FB5
13
ONA
6
VIN
D1
CSA
10
VA
9
FBA
R5
50k
100k
12V
R6
3.6k
EXT
1
3300pF
SS5
7
C7
8
144 PGNDGND
SSA
C6
3
REF
ON/OFF
4.7µFC15
0.47µF
C14
0.1µF
+30V
Figure 11. Negative 30V Auxiliary Output Application Circuit
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX624
Dual-Output, 1MHz DC-DC Boost Converter
for PCMCIA Applications
___________________Chip Topography
TRANSISTOR COUNT: 926
SUBSTRATE CONNECTED TO GND
ONA
SHDN
GND
REF
RESET EXT VIN LX5
0.149"
(3.785mm)
0.085"
(2.159mm)
SS5 SSA VAFBA
CSA
DA
FB5
PGND
