19-1406; Rev 1; 1/99
KIT
ATION
ET
EVALU
TA SHE
WS DA
FOLLO
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
General Description
The MAX1729 micropower step-up/step-down DC-DC
converter is ideally suited for electrically controlled bire-
fringence (ECB) and liquid-crystal-display (LCD) bias-
supply generation. It provides step-up/step-down
voltage conversion and reduces output ripple by using
a step-up DC-DC converter followed by a linear regula-
tor. This architecture permits a physically smaller induc-
tor than those used in competing SEPIC and flyback
topologies. This device features low quiescent current
(67µA typical). A logic-controlled shutdown mode fur-
ther reduces quiescent current to 0.4µA typical.
The MAX1729 features an input that dynamically
adjusts the output voltage to control display color or
contrast. It offers two feedback modes: internal and
external. Internal feedback mode allows output volt-
ages between 2.5V and 16V, and is specifically
designed to hold temperature drift to ±11ppm/°C.
External feedback mode allows the MAX1729 output
voltage range to be tailored for various displays.
An on-chip temperature sensor with a positive tempera-
ture coefficient provides compensation for LCD/ECB
display temperature characteristics. In internal feed-
back mode, the buffered temperature sensor output is
read and used to adjust the output voltage via a digital
control signal. External feedback mode features an
additional compensation method in which the tempera-
ture output is summed directly into the feedback net-
work to provide first-order negative temperature
compensation of the output voltage. The MAX1729 is
available in the space-saving 10-pin µMAX package.
o
±11ppm/°C Output Voltage Drift
o
On-Chip Temperature Sensor Output
o
Accurate Voltage and Temperature Provide:
Consistent ECB Colors
Consistent LCD Gray-Scale Contrast
o
+2.7V to +5.5V Input Voltage Range
o
Output Voltage Range
+2.5V to +16V in Internal Feedback Mode
Programmable in External Feedback Mode
o
Dynamic Control of the Output Voltage
o
67µA Supply Current
o
0.4µA Shutdown Current
o
10-Pin µMAX Package (1.09mm max height)
o
Evaluation Kit Available (MAX1729EVKIT)
Features
o
High-Accuracy Reference Voltage (±1%)
MAX1729
Ordering Information
PART
MAX1729EUB
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
10 µMAX
Applications
ECB Display Bias & Color Adjustment
LCD Display Bias & Contrast Adjustment
Cellular Phones
Personal Digital Assistants
V
IN
2.7V to 5.5V
Typical Operating Circuit
IN
GND
LX
PS
Pin Configuration
TOP VIEW
IN
1
TC
REF
COMP
FB
2
3
4
5
10
GND
9
LX
PS
OUT
CTLIN
DIGITAL
PWM
CONTROLLER
ADC
REF
MAX1729
OUT
V
OUT
+2.5V to +16V
CTLIN
FB
MAX1729
8
7
6
TC
COMP
µMAX
________________________________________________________________
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 1-800-835-8769.
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +6V
LX, PS, OUT to GND...............................................-0.3V to +20V
CTLIN, FB, REF, COMP, TC to GND ...........-0.3V to (V
IN
+ 0.3V)
LX to PS ..................................................................-20V to +1.0V
LX, PS, OUT Current ...........................................................60mA
Continuous Power Dissipation (T
A
= +70°C)
10-pin µMAX (derate 5.6mW/°C above +70°C) ..........444mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= +3V, CTLIN = IN, FB = GND, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
Undervoltage Lockout
Threshold (Note 2)
IN Supply Current
PS Supply Current
Shutdown Supply Current
Reference Output Voltage
SYMBOL
V
IN
V
LO
I
IN
I
PS
I
SHDN
V
REF
V
OUT
(MIN)
CONDITIONS
MIN
2.7
2.0
TYP
MAX
5.5
2.6
UNITS
V
V
µA
µA
µA
V
37
30
CTLIN = GND, I
SHDN
= I
IN
+ I
PS
I
REF
= 0
FB = GND, CTLIN =
0.1% duty cycle,
I
OUT
= 0 to 0.5mA
I
OUT
= 0 to 0.5mA
FB = GND, CTLIN =
0.1% to 100% duty
cycle, I
OUT
= 0
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
0.5
T
A
= +25°C
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= -40°C to +85°C
V
FB
= +1.25V
V
IN
= +5.5V
V
IN
= +2.7V
2
1.3
1.178
15.5
14.5
±50
1.215
1.200
90
122
5
1.228
T
A
= +25°C
T
A
= -40°C to +85°C
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
1.215
1.200
2.35
2.35
16
13.90
13.60
±11
±18
2.5
1.228
16.5
16.5
16.40
13.95
2.45
0.4
1.228
50
40
2
1.241
1.256
2.5
Minimum Output Voltage
V
2.52
V
14.00
V/100%
14.20
±30
±65
1.278
17.5
18.5
1.241
1.256
150
50
ppm/°C
mA
V
mV/°C
µA
V
mV
nA
V
Maximum Output Voltage
V
OUT
(MAX)
CTLIN to V
OUT
Gain
Output Voltage
Temperature Coefficient
Maximum Output Current
TC Output Voltage
TC Output Temperature
Coefficient (Note 3)
TC Output Current
Feedback Set Voltage (FB)
FB Mode Threshold
FB Bias Current
CTLIN High Voltage
TC
OUT
I
OUT
V
TC
TC
TC
I
TC
V
FB
V
MODE
I
FB
V
IH
V
PS
= +18V (Note 3)
2
_______________________________________________________________________________________
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
ELECTRICAL CHARACTERISTICS
(V
IN
= +3V, CTLIN = IN, FB = GND, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
CTLIN Low Voltage
CTLIN Bias Current
COMP Impedance
CTLIN Minimum Pulse Width
for Shutdown
CTLIN Minimum Pulse Width
for V
OUT
Control
COMP Rise/Fall Time
Switch On-Resistance
Switch Off-Leakage Current
LX to PS Diode Forward
Voltage
PFM On-Time Constant
PS to OUT Voltage (Note 5)
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
SYMBOL
V
IL
I
IHL
R
COMP
t
OFF
t
CTLIN
t
R
/t
F
R
ON
I
LX(OFF)
V
LX-PS
K
V
FB
= +1.25V
I
LX
= 30mA
V
LX
= 18V
I
DIODE
= 30mA
T
A
= +25°C
T
A
= -40°C to +85°C
6
5
0.4
V
IN
= +2.7V
V
IN
= +5.5V
CONDITIONS
V
IN
= +2.7V to +5.5V
V
IN
= +5.5V, CTLIN = GND or IN
V
FB
= 0, Internal Feedback Mode
V
FB =
+1.25V, External Feedback Mode
(Note 4)
700
33
60
1250
25
20
2.5
1.5
0.1
700
8
0.6
1
970
10
11
1.0
5.0
150
2400
MIN
TYP
MAX
0.4
±1
UNITS
V
µA
kΩ
Ω
µs
ns
ns
Ω
µA
mV
V-µs
V
Specifications to -40°C are guaranteed by design, not production tested.
When V
IN
is below this level, the boost and LDO outputs are disabled.
Guaranteed by design.
Minimum time to hold CTLIN low to invoke shutdown. If CTLIN is held low for less than t
OFF
, device does not enter shutdown.
Switching regulator regulates this voltage to keep LDO from dropping out.
_______________________________________________________________________________________
3
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
Typical Operating Characteristics
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 9.4 (CTLIN AT 50% DUTY CYCLE)
MAX1729 toc 01
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 16.4 (CTLIN = IN)
MAX1729 toc 02
NO-LOAD SUPPLY CURRENT vs.
SUPPLY VOLTAGE
MAX1729 toc 03
60
60
0.40
0.35
SUPPLY CURRENT (mA)
0.30
0.25
0.20
0.15
0.10
0.05
V
OUT
= 9.4V
V
OUT
= 2.5V
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V
OUT
= 16.4V
50
V
IN
= 2.7V
EFFICIENCY (%)
40
30
20
10
0
0.01
0.1
1
50
EFFICIENCY (%)
40
30
20
10
0
V
IN
= 2.7V
V
IN
= 5.5V
V
IN
= 5.5V
10
0.01
0.1
1
10
6.0
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
MAX1729 toc 04
PS TO OUT (LDO)
POWER-SUPPLY REJECTION RATIO
MAX1729 toc 05
SHUTDOWN SUPPLY CURRENT
MAX1729 toc 06
7
MAXIMUM OUTPUT CURRENT (mA)
6
5
4
3
2
1
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V
OUT
= 16.4V
V
OUT
= +2.5V
0
3.0
2.5
SHUTDOWN CURRENT (µA)
2.0
1.5
1.0
0.5
0
-20
PSRR (dB)
6.0
V
OUT
= 9.4V
-40
-60
-80
-100
1
10
100
1k
10k
100k
SUPPLY VOLTAGE (V)
FREQUENCY (Hz)
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
INPUT VOLTAGE (V)
OUTPUT VOLTAGE vs.
DUTY CYCLE
MAX1729 toc 07
START-UP DELAY FROM SHUTDOWN
MAX1729 toc 08
DELAY TO SHUTDOWN
MAX1729 toc 09a
18
16
14
OUTPUT VOLTAGE (V)
12
10
8
6
4
2
0
0
V
CTLIN
5V/div
V
REF
1V/div
V
CTLIN
5V/div
V
REF
1V/div
V
TC
1V/div
V
OUT
10V/div
10 20 30 40 50 60 70 80 90 100
DUTY CYCLE (%)
20ms/div
V
IN
= 5V
I
O
= 0.5mA
V
TC
1V/div
V
OUT
10V/div
V
IN
= 5V
I
O
= 0.5mA
500ms/div
4
_______________________________________________________________________________________
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
Typical Operating Characteristics (continued)
(Circuit of Figure 2, T
A
= +25°C, unless otherwise noted.)
DELAY TO SHUTDOWN
MAX1729 toc 09b
SWITCHING WAVEFORMS
HEAVY LOAD
MAX1729 toc 10
SWITCHING WAVEFORMS
MEDIUM LOAD
I
L
20mA/div
MAX1729 toc 11
V
CTLIN
5V/div
V
REF
1V/div
I
L
20mA/div
V
TC
1V/div
V
OUT
10V/div
5ms/div
V
IN
= 5V
I
O
= 0.5mA
OUTPUT
RIPPLE
10mV/div
OUTPUT
RIPPLE
10mV/div
V
LX
5V/div
V
LX
5V/div
2µs/div
2µs/div
LOAD-TRANSIENT RESPONSE
MAX1729 toc 13
LINE-TRANSIENT RESPONSE
CTLIN = IN
I
OUT
= 0.5mA
V
OUT
20mV/div
16.400
5V
4V
MAX1729 toc 14
16.404
V
OUT
20mV/div
500µA
I
OUT
250µA/div
20µA
1ms/div
V
IN
1V/div
2ms/div
_______________________________________________________________________________________
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