MAX749CPA+-MAX749CSA+-MAX749CSA+T-MAX749ESA+-MAX749ESA+T Fast Delivery |IC PHOENIX CO.,LIMITED

MAX749ESA+T ,Digitally Adjustable LCD Bias SupplyMAX74919-0143; Rev 1; 2/95Digitally Adjustable LCD Bias Supply_______________
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MAX749CPA+-MAX749CSA+-MAX749CSA+T-MAX749ESA+-MAX749ESA+T
Digitally Adjustable LCD Bias Supply
Digitally Adjustable LCD Bias Supply
_______________General Description
The MAX749 generates negative LCD-bias contrast
voltages from 2V to 6V inputs. Full-scale output voltage
can be scaled to -100V or greater, and is digitally
adjustable in 64 equal steps by an internal digital-to-
analog converter (DAC). Only seven small surface-
mount components are required to build a complete
supply. The output voltage can also be adjusted using
a PWM signal or a potentiometer.
A unique current-limited control scheme reduces supply
current and maximizes efficiency, while a high switching
frequency (up to 500kHz) minimizes the size of external
components. Quiescent current is only 60μA max and is
reduced to under 15μA in shutdown mode. While shut
down, the MAX749 retains the voltage set point, simpli-
fying software control. The MAX749 drives either an
external P-channel MOSFET or a PNP transistor.
________________________Applications
Notebook Computers
Laptop Computers
Palmtop Computers
Personal Digital Assistants
Communicating Computers
Portable Data-Collection Terminals
____________________________Features+2.0V to +6.0V Input Voltage RangeFlexible Control of Output Voltage:
Digital Control
Potentiometer Adjustment
PWM ControlOutput Voltage Range Set by One ResistorLow, 60μA Max Quiescent Current15μA Max Shutdown ModeSmall Size – 8-Pin SO and Plastic DIP Packages
_______________________________________________________________Maxim Integrated Products 1
DHI
DLOW
GNDFB
CTRL
ADJ
DIP/SO
TOP VIEW
MAX749
__________________Pin Configuration
ADJ
CTRL
DHI
DLOW
GND
VIN +5V
-VOUT
RSENSE
CCOMP
ON/OFF
DIGITAL
ADJUST
RFB0.1μF5
MAX749
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0143; Rev 1; 2/95
PARTTEMP. RANGEPIN-PACKAGE
MAX749CPA0°C to +70°C8 Plastic DIP
MAX749CSA0°C to +70°C8 SO
MAX749EPA-40°C to +85°C8 Plastic DIP
MAX749ESA-40°C to +85°C8SO
MAX749C/D0°C to +70°CDice*
______________Ordering Information
* Contact factory for dice specifications.
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
= TMINto TMAXMINMAX
Digitally Adjustable LCD Bias Supply______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS................................................................................-0.3V, +7V
CTRL, ADJ, FB, DLOW, DHI, CS.....................-0.3V, (V++ 0.3V)
Continuous Power Dissipation (TA= +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C)............727mW
SO (derate 5.88mW/°C above +70°C).........................471mW
Operating Temperature Ranges:
MAX749C_A........................................................0°C to +70°C
MAX749E_A.....................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
ELECTRICAL CHARACTERISTICS
(2V < V+ < 6V, TA= TMINto 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.
Note 1:The device is in regulation when VFB= 0V (see Figures 3 - 6).
Note 2:These tests performed at V+ = 3.3V. Operation over supply range is guaranteed by supply rejection test of full-count current.
Note 3:VIHis guaranteed by design to be 1.8V min for V+ = 2Vto 6V for TA= TMINto TMAX. VILis guaranteed by design from = TMINto TMAX.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
V+ Voltage26V
FB Source CurrentIFBSOn power-up or reset, VFB= 0V (Note 1)12.8013.3313.86μA
Zero-Count FBCurrentVFB= 0V0.450.55IFBS
Full-Count FB CurrentVFB= 0V1.431.53IFBS
DAC Step Size (Note 2)Monotonicity guaranteed, VFB= 0V1.001.562.12%IFBS
DAC Linearity (Note 2)VFB= 0V±1%IFBS
Supply RejectionV+ = 2V to 6V, full-count current1.5%IFBS
Switching Frequency100 to 500kHz
Logic Input Current0V < VIN< V+, CTRL, ADJ±100nA
Logic High Threshold (Note 3)VIHCTRL, ADJ1.6V
Quiescent Current60μA
Shutdown Current15μAto CSVoltageCurrent-limit trip voltage110140180mV
DHI Source CurrentV+ = 2V, VDHI= 1V2450mA
DHI Drive LevelNo loadV+ - 50mVV+V
DLOWOnResistanceV+ = 2V, VDLOW= 0.5V510ΩLogic Low Threshold (Note 3)VILCTRL, ADJ0.4
TIMING CHARACTERISTICS= +25°C
MINTYPMAXPARAMETERSYMBOLCONDITIONSUNITS
Minimum Reset Pulse WidthtRV+ = 5V100
Minimum Reset SetuptRS00
Minimum Reset HoldtRH
Not tested0
tSHV+ = 2V1585100Minimum ADJ High Pulse WidthV+ = 5V1085100
tSLV+ = 2V170400500Minimum ADJ Low Pulse WidthV+ = 5V60150200
Minimum ADJ Low to CTRL LowtSDV+ = 2V70200250
V+ = 5V2085100V+ = 2V40085
Not tested
FB Offset Voltage±15mV
Digitally Adjustable LCD Bias Supply
_______________________________________________________________________________________ 3
EFFICIENCY vs.
OUTPUT VOLTAGE
MAX749-TOC1-A
OUTPUT VOLTAGE (V)
(%
-40mA
V+ = 3V
RBASE = 470Ω
RSENSE = 0.25Ω
TRANSISTOR : ZTX750
-20mA
-5mA
EFFICIENCY vs.
OUTPUT VOLTAGE
MAX749-TOC1-B
OUTPUT VOLTAGE (V)
FIC
(%
-5mA-20mA
-40mA
V+ = 5V
RSENSE = 0.25Ω
TRANSISTOR : SMD10P05L
EFFICIENCY vs. OUTPUT
CURRENT – PNP
MAX749TOC2-A
OUTPUT CURRENT (mA)
(%20304050
-24V
-12V
-5V
V+ = 3V
RBASE = 470Ω
RSENSE = 0.25Ω
TRANSISTOR: ZTX7502060100
EFFICIENCY vs. OUTPUT
CURRENT – PNP
MAX749TOC2-B
OUTPUT CURRENT (mA)
(%8030507090V+ = 3V
RBASE = 160Ω
RSENSE = 0.25Ω
TRANSISTOR = ZTX750
-12V
-5V
-24V
LOAD CURRENT vs. INPUT VOLTAGE
MAX749-TOC3-B
INPUT VOLTAGE (V)
(m
-5V
-12V
-24V
-48V
RBASE = 160Ω
RSENSE = 0.25Ω
TRANSISTOR = ZTX750103050
EFFICIENCY vs. OUTPUT
CURRENT – MOSFET
MAX749TOC2-C
OUTPUT CURRENT (mA)
(%4015253545
V+ = 5V
RSENSE = 0.25Ω
TRANSISTOR: SMD10P05L
-12V
-5V
-24V
LOAD CURRENT vs. INPUT VOLTAGE
AX749-TOC3-A
INPUT VOLTAGE (V)
(m
RBASE = 470Ω
RSENSE = 0.25Ω
TRANSISTOR = ZTX750
-5V
-12V
-24V
-48V
__________________________________________Typical Operating Characteristics
(TA = +25°C, L = 47μH, unless otherwise noted.)
Digitally Adjustable LCD Bias Supply______________________________________________________________________________________
PINNAMEFUNCTIONV++2V to +6V Input Voltage to power the MAX749 and external circuitry. When using an external
P-channel MOSFET, V+ must exceed the MOSFET’s gate threshold voltage.ADJ
Logic Input. When CTRL is high, a rising edge on ADJ increments an internal counter. When CTRL is
low, the counter is reset to mid-scale when ADJ is high. When ADJ is low, the counter does not
change (regardless of activity on CTRL) as long as V+ is applied.CTRL
Logic Input. When CTRL and ADJ are low, the MAX749 is shut down, but the counter is not reset.
When CTRL is low, the counter is reset to mid-scale when ADJ is high. The device is always on when
CTRL is high.FBFeedback Input for output full-scale voltage selection. -VOUT(MAX)= (RFB) x (20μA) where RFBis
connected from FB to -VOUT. The device is in regulation when VFB= 0V.GNDGroundDLOW
Output Driver Low. Connect to DHI when using an external P-channel MOSFET. When using an
external PNP transistor, connect a resistor RBASEfrom DLOW to the base of the PNP to set the maxi-
mum base-drive current.DHIOutput Driver High. Connect to the gate of the external P-channel transistor, or to the base of the
external PNP transistor.CSCurrent-Sense Input. The external transistor is turned off when current through the sense resistor,
RSENSE, brings CS below V+ by 140mV (typ).
OUTPUT
VOLTAGE
LOAD
CURRENT
100mVAC/div
10mA/div
0mA
LOAD-TRANSIENT RESPONSE
VOUT = -15V
TRANSISTOR = ZTX750
50μs/div
VOUT = -15V
TRANSISTOR = ZTX750
OUTPUT
VOLTAGE
INPUT
VOLTAGE
100mVAC/div
1 V/div
LINE-TRANSIENT RESPONSE
VOUT = -15V
ILOAD = 5mA
TRANSISTOR = ZTX750
50ms/div
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, L = 47μH, unless otherwise noted.)
______________________________________________________________Pin Description
_______________Detailed Description
The MAX749 is a negative-output inverting power con-
troller that can drive an external PNP transistor or P-
channel MOSFET. An external resistor and an internal
DAC control the output voltage (Figure 1).
The MAX749 is designed to operate from 2V to 6V inputs,
ideal for operation from low-voltage batteries. In systems
with higher-voltage batteries, such as notebook comput-
ers, the MAX749 may also be operated from the regulat-
ed +5V supply. A high-efficiency +5V regulator, such as
the MAX782, is an ideal source for the MAX749. In this
example, the MAX749 efficiency (80%) is compounded
with the MAX782 efficiency (95%): 80% x 95% = 76%,
which is still high.
Operating Principle
The MAX749 and the external components shown in the
Typical Operating Circuitform a flyback converter.
When the external transistor is on, current flows through
the current-sense resistor, the transistor, and the coil.
Energy is stored in the core of the coil during this phase,
and the diode does not conduct. When the transistor
turns off, current flows from the output through the diode
and the coil, driving the output negative. Feedback con-
trol adjusts the external transistor’s timing to provide a
regulated negative output voltage.
The MAX749’s unique control scheme combines the
ultra-low supply current of pulse-skipping, pulse-fre-
quency modulation (PFM) converters with the high full-
load efficiency characteristic of pulse-width modulation
(PWM) converters. This control scheme allows the
device to achieve high efficiency over a wide range of
loads. The current-sense function and high operating
frequency allow the use of tiny external components.
Switching control is accomplished through the combi-
nation of a current limit in the switch plus on- and off-
time limits (Figure 2).
Once turned on, the transistor stays on until either:
- the maximum on-time one-shot turns it off
(8μs later), or
- the switch current reaches its limit (as determined
by the current-sense resistor and the current
comparator).
Digitally Adjustable LCD Bias Supply
_______________________________________________________________________________________ 5
L1
47μH
DLOW
SWITCH-
MODE
POWER
SUPPLY
6-BIT
CURRENT-OUTPUT
DAC
REF
LOGIC
BIAS
POWER-ON
RESET
6-BIT
COUNTER
MAX749
VOUT
(NEGATIVE)
CTRL
ADJ
RESET
INCREMENT
ON/OFF
+2V TO +6V
INPUT22μF
6.2V
6.66μA TO 20μA
DHI
GND
RSENSE
Q1
ZTX750
D1
1N5819RBASE
470Ω
22μF
30VCCOMP
RFB
0.1μF
Figure 1.Block Diagram, Showing External Circuitry Using a PNP Transistor
Once turned off, a one-shot holds the switch off for a
minimum of 1μs, and the switch either stays off (if the
output is in regulation), or turns on again (if the output
is out of regulation).
With light loads, the transistor switches for one or more
cycles and then turns off, much like a traditional PFM
converter. With heavy loads, the transistor stays on until
the switch current reaches the current limit; it then
shuts off for 1μs, and immediately turns on again until
the next time the switch current reaches its limit. This
cycle repeats until the output is in regulation.
Output Voltage Control
The output voltage is set using a single external resistor
and the internal current-output DAC (Figure 1). The full-
scale output voltage is set by selecting the feedback
resistor, RFB. The output voltage is controlled from 33%
to 100% of the full-scale output by an internal 64-step
DAC/counter.
On power-up or after a reset, the counter sets the DAC
output to mid-range. Each rising edge of ADJ incre-
ments the DAC output. When incremented beyond full
scale, the counter rolls over and sets the DAC to the
minimum value. In this way, a single pulse applied to
ADJ increases the DAC set point by one step, and 63
pulses decrease the set point by one step.
Table 1 is the logic table for the CTRL and ADJ inputs,
which control the internal DAC and counter. Figures 3-7
show various timing specifications and different ways of
incrementing and resetting the DAC, and of placing it in
the low-power standby mode. As long as the timing
specifications for ADJ and CTRL are observed, any
sequence of operations can be implemented.
Table 1. Input Truth Table
Digitally Adjustable LCD Bias Supply______________________________________________________________________________________
L1
47μH
DLOW
6-BIT
CURRENT-OUTPUT
DAC
REF
MAXIMUM
ON-TIME
ONE-SHOT
MAX749
VOUT
(NEGATIVE)
22μF
0.1μF
DHI
GND
RSENSE
Q1
ZTX750
D1
1N5819
RBASE
470Ω
22μF
30V
CCOMP
RFB
TRIG
MINIMUM
OFF-TIME
ONE-SHOT
TRIGQS
FLIP-FLOP
VOLTAGE
COMPARATOR
140mV
+2V TO +6V
INPUT
CURRENT
COMPARATOR
Figure 2.Switch-Mode Power-Supply Section Block Diagram
ADJCTRLRESULT
LowLowShut down
HighLowReset counter to mid-range. The
device is not shut down.HighOn
HighIncrement the counter

Partno	Mfg	Dc	Qty	Available	Descript
MAX749CPA+	MAXIM	N/a	1500	avai	Digitally Adjustable LCD Bias Supply
MAX749CSA+	MAXIM	N/a	3400	avai	Digitally Adjustable LCD Bias Supply
MAX749CSA+T \|MAX749CSAT	MAXIM	N/a	2500	avai	Digitally Adjustable LCD Bias Supply
MAX749ESA+	MAXIM	N/a	3400	avai	Digitally Adjustable LCD Bias Supply
MAX749ESA+T \|MAX749ESAT	MAXIM	N/a	15000	avai	Digitally Adjustable LCD Bias Supply