ZXLB1600
LCD AND OLED BIAS BOOST CONVERTER - STN, CSTN SCREENS
DESCRIPTION
The ZXLB1600 inductive switching boost converter
accepts an input voltage of between 1.6V and 5.5V and
provides an adjustable output voltage of up to 28V for
LCD and OLED bias. The device contains an output
switch and a second switch to isolate the coil from the
input to provide true isolation in shutdown mode. The
output can be adjusted by means of an externally
applied dc voltage, a PWM control signal, or external
feedback resistors and can supply typically 10mA of
output current at maximum output voltage. Higher
current is available at lower output voltages.
The input voltage range accepts a number of battery
solutions, including dual dry cell and single Li-Ion cells
and PFM operation mode allows the output to be
regulated with high efficiency under light or no load
conditions. The switching frequency range permits the
use of miniature surface mount inductors.
A low battery comparator is provided to indicate when
the input voltage has fallen to within
±2%
of a preset
threshold. This threshold is set internally , but can be
adjusted externally to any voltage within the supply
voltage range.
FEATURES
•
Wide input voltage range: 1.6 to 5.5V
•
Adjustable output voltage up to 28V, using PWM
or analog control voltage
Internal PWM filter
True shutdown (output isolated from input)
Internal output switch and current sense
Low quiescent current: (75 A max)
5 A (max) shutdown current (including low
battery comparator)
Up to 500kHz switching frequency
High efficiency
Small MSOP10 package
Low external component count
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APPLICATIONS
PDAs
Mobile phones - OLED sub displays
Digital cameras
Portable internet appliances
Palmtop computers
•
GPS terminals
TYPICAL APPLICATION CIRCUIT
ISSUE 3 - SEPTEMBER 2003
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SEMICONDUCTORS
ZXLB1600
ABSOLUTE MAXIMUM RATINGS
(Voltages to GND unless otherwise stated)
Output voltage
Input voltage
Switch output current
Power dissipation
Operating temperature
Storage temperature
Junction temperature
30V
7V
500mA
800mW
0 to 70 C
-55 to 125 C
150 C
ELECTRICAL CHARACTERISTICS
Test conditions unless otherwise stated: V
IN
= 3.0V, T
AMB
= 25°C
Symbol
General
V
IN
I
IN
Input voltage
(1)
Supply current Shutdown
Quiescent
Isolating switch
R
ISO
I
ISO
V
SW(max)
LX Switch
I
LX
R
LX
I
LX(leak)
V
LX
V
OUT
I
OUT
V
LNR
V
LDR
f
LX
T
ON
T
OFF
Switch peak current limit
(3)
‘On’ resistance
Switch leakage current
Operating voltage on LX pin
-0.5
0.15
0.5
0.35
2
1
30
V
A
A
‘On’ resistance
Leakage current
Maximum voltage on SW pin
during normal operation
V
EN
= V
IN
V
EN
= 0V
0.7
2
1
V
IN
+0.5 V
A
(2)
Parameter
Conditions
Min
Typ
Max
Units
1.6
V
EN
= 0V
V
EN
= V
IN
, I
OUT
= 0V, Not
switching
3.5
30
5.5
5
75
V
A
A
Controller output
Output voltage range
Output current
Line regulation
Load regulation
Operating frequency
Output ‘ON’ time
Output ‘OFF’ time
Efficiency
(4)
LX output low
LX output off
Lx = 22 H, V
OUT
= 20V
0.9
80
Lx = 22 H, V
OUT
= 28V
I
OUT
= 1mA, 2V < V
IN
<5.5V
V
OUT
= 28V, 100 A < I
OUT
< 5mA
V
IN
5
10
0.1
0.15
500
10
28
V
mA
%/V
%/mA
kHz
s
µs
%
Note:
1) Minimum supply voltage should be maintained above 2V for operation at minimum temperature.
2) Shutdown current includes the operating current for the low battery comparator, which remains active in shutdown mode.
3) This is the dc value. The dynamic value may exceed 350mA during normal operation, due to switching delays, coil inductance and supply
voltage.
4) Efficiency is dependent upon the choice of external components, input/output voltages and load current.(see typical operating curves).
ISSUE 3 - SEPTEMBER 2003
SEMICONDUCTORS
2
ZXLB1600
ELECTRICAL CHARACTERISTICS
(Cont.)
Test conditions unless otherwise stated: V
IN
= 3.0V, T
AMB
= 25°C
Symbol
Parameter
Conditions
Min Typ
Max
Units
Output voltage control by dc voltage applied to ‘ADJ’ pin
V
ADJ (nom)
V
ADJ
Internal reference voltage
Temperature coefficient of V
ADJ
External overdrive voltage range
on ‘ADJ’ pin for output voltage
control
Input current into V
ADJ
pin
Default Output voltage
‘ADJ’ pin floating, ‘EN’= V
IN
0.5
1.23
40
V
ADJ
(NOM)
V
ppm/ C
V
0.5<V
ADJ
< V
ADJ (NOM)
V
SENSE
‘ADJ’ pin floating, ‘EN’= V
IN
Output voltage control by PWM signal applied to ‘EN’ input
∆T/T
f
LPF
A
LPF
R1
R2
Enable input
V
ENL
V
ENH
I
ENL
I
ENH
T
EN(hold)
V
LBT
V
BLHYS
Ref
(LBD)
V
LBT (max)
I
BLOL
V
BLOL
I
BLOH
V
BLOH
R3
R4
Note:
5)
6)
I
ADJ
-10
27
29
V
A
PWM duty cycle range at ‘EN’
input
Internal low pass filter cut-off
frequency
Filter attenuation
10kHz
(5)
< f < 100kHz, V
ENH
=V
IN
40
4
100
%
kHz
dB
f=30kHz
52.5
Internal voltage setting resistors for output voltage
Ref. Block diagram
317
6.93
k
M
Low level Input voltage
High level Input voltage
Low level input current
High level input current
Enable active hold time
(6)
Device in shutdown
Device active
V
EN
=0V
V
EN
=V
IN
V
EN
switched from high to low
V
IN
falling
V
IN
rising
1.94
20
20
1.21
120
1.4
0.4
Vin
-100
100
V
V
nA
nA
s
Low-battery detection circuit
Detection threshold
Temperature coefficient of V
BLT
Hysteresis
Internal reference voltage
Maximum voltage on LBT pin
Low level output current
Low level output voltage
High level output current
High level output voltage
Output ‘on’
I
BLOL
= 0.5mA
Output ‘off’ , V
BLOH
= 29V
Output ‘off’
2.02
V
ppm/ C
mV
V
V
in
-0.5 V
1
0.4
2
29
V
mA
V
A
Internal voltage setting resistors for low-battery detection circuit
Ref. block diagram
1.56
2.44
M
M
This is the minimum PWM frequency to maintain a continuous output. Lower frequencies can be used, but will result in gated operation of
the device i.e. device enters shutdown when EN is low (see Note 6).
This is the time for which the device remains active after the EN pin has been driven low. This delay allows a continuous output to be
maintained during PWM mode operation at frequencies higher than 10kHz.
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SEMICONDUCTORS
ZXLB1600
PIN CONNECTIONS
PIN DESCRIPTION
Pin #
1
2
3
4
5
6
7
Name
ADJ
EN
VIN
SW
SENSE
LX
LBF
Description
Internal (or external) reference voltage.
Can be overdriven to adjust output voltage
Enable input (active high)
Also used to adjust output voltage by PWM signal
Input voltage
Output of high side PMOS isolation switch
Output voltage sense
Output of NMOS switch
Low battery flag output: open drain
(active low for low battery voltage)
Active when EN is high or low
8
9
10
GND
FB
LBT
Ground
Voltage feedback pin for output (threshold 1.23V)
Low battery flag threshold adjust input
(threshold 1.21V)
ORDERING INFORMATION
DEVICE
ZXLB1600X10TA
ZXLB1600X10TC
TA reels 1k,
TC reels 4k devices.
DEVICE DESCRIPTION
Boost converter for LCD bias in MSOP10
Boost converter for LCD bias in MSOP10
TEMPERATURE
RANGE
0 C to 70 C
0 C to 70 C
PART MARK
ZXLB1600
ZXLB1600
ISSUE 3 - SEPTEMBER 2003
SEMICONDUCTORS
4
ZXLB1600
BLOCK DIAGRAM
Device description
The device is a flyback boost converter, working in
discontinuous mode.
With reference to the chip block diagram and typical
application circuit, the operation of the device is as
follows:
Setting output voltage
With external voltage
The output voltage is equal to the voltage present on
the 'ADJ' pin of the device multiplied by the internal
resistor network factor (R1+R2)/R1. The ADJ pin is
connected to the internal reference voltage of value
V
ADJ(nom)
and by default will give a nominal output of
28V. However, if required, the ADJ pin may be
overdriven with an external dc voltage V
ADJ
, in order to
adjust the output voltage to a value lower than the
default value.
Control loop
When 'EN' is high, the control circuits become active. The
high side of the coil is connected to the input via a large
PMOS isolating switch (MP) and the low side to ground via
NDMOS transistor (MN). The current in the coil is allowed
to build up to an internally defined level (nominally 200 to
300mA) before MN is turned off. The energy stored in the
coil is then transferred to the output capacitor (C2) via
diode (D1). The output voltage is sensed at pin 'SENSE' by
internal resistors R1 and R2 (which may be shunted
externally at pin 'FB') and compared to a reference voltage
(1.23V nominal). A comparator senses when the output
voltage is above that set by the reference and its output is
used to control the 'off' time of the output switch. The
control loop is self-oscillating, producing pulses of 10 s
maximum duration (switch 'on'), at a frequency that varies
in proportion to the output load current. The minimum
'off' time of the output switch is fixed at 1.25 s nominal, to
allow time for the coil's energy to be dissipated before the
switch is turned on again. This maintains stable and
efficient operation.
ISSUE 3 - SEPTEMBER 2003
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SEMICONDUCTORS
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