MAX1620EEE+ Maxim Integrated Products, MAX1620EEE+ Datasheet - Page 10

• Manufacturer Part Number: MAX1620EEE+
• Description: IC LCD BIAS SUPP DGTL ADJ 16QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1620EEE+

• Applications: LCD Display
• Current - Supply: 150µA
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Output Current: 0.07 A
• Input Voltage: 1.8 V to 20 V
• Switching Frequency: 300 KHz
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX1620/MAX1621 are step-up power controllers
that drive an external N-channel FET or NPN transistor
to convert power from a 1.8V to 20V battery to a higher
positive or negative voltage. They are configured as
negative-output, inverting power controllers with one
additional diode and one additional capacitor. Either
configuration’s output voltage can be adjusted with
external resistors, or digitally adjusted with an internal
digital-to-analog converter (DAC). The MAX1620 uses
pin-defined controls for the DAC, while the MAX1621
communicates with the DAC via the SMBus™ interface.
The MAX1620/MAX1621 operate in discontinuous-
conduction mode (where the inductor current ramps to
zero by the end of each switching cycle) and with a
constant peak current, without requiring a current-
sense resistor. Switch on-time is inversely proportional
to the input voltage V
stant, or k-factor, of 20µs-V (e.g., for V
on-time = 2µs).
For an ideal boost converter operating in discontinu-
ous-conduction mode (no power losses), output current
is proportional to input voltage and peak inductor current:
I
parts, is determined by the k-factor:
Figure 4. Typical Operating Circuit—Positive Output
Digitally Adjustable LCD Bias Supplies
10
_______________Detailed Description
PK
5.5V
12V
TO
is proportional to on-time (t
2V
3V
TO
______________________________________________________________________________________
NOTE: CONNECTIONS TO DIGITAL INPUTS NOT SHOWN.
I
OUT
R2
100k
R1
360k
C1
0.1 F
C2
0.1 F
1
2
I
R8
10k
D3 1N6263 (ANY SCHOTTKY)
PK
11
12
3
5
7
4
1
2
6
BATT
= k-factor / L
I
BATT
POK
V
POL
SHDN (SUS)
DN (SDA)
UP (SCL)
REF
AGND
PK
DD
TO REF
( ) ARE FOR MAX1621.
by a microsecond-volt con-
MAX1620
MAX1621
V
Operating Principle
BATT
U1
ON
), which, for these
/ V
LCDON
PGND
DOUT
OUT
DLO
DHI
LX
FB
BATT
14
16
15
13
10
9
8
C3
22 F
= 10V,
300k
R3
Discontinuous conduction is detected by monitoring the
LX node voltage. When the inductor’s energy is com-
pletely delivered, the LX node voltage snaps back to
the BATT voltage. When this crossing is sensed, anoth-
er pulse is issued if the output is still out of regulation.
To select a positive output voltage, tie the polarity pin
(POL) to V
in Figure 4. FB regulation voltage is 1.5V. For optimum
stability, V
To select a negative output voltage, tie POL to GND
(Figure 5). In this configuration, the internal error amplifi-
er’s output is inverted to provide the correct feedback
polarity. FB regulation voltage is 0V. D1, D2, C4, and C5
form an inverting charge pump to generate the negative
voltage. This allows application of the positive boost
switching topology to negative output voltages.
The negative output circuit has two possible connec-
tions. In the standard connection, D1’s cathode is con-
nected to BATT. This connection features the best
output ripple performance, but V
to no more than 27V - 1.1(V
voltage is needed, an alternative connection allows a
maximum negative output of -27V, but with the addition-
al constraint that V
native circuit, connect D1’s cathode to ground rather
than BATT (Figure 6). Increase C4 to 2.2 F to improve
output ripple performance.
The negative charge pump limits the output current to
the charge transferred each cycle multiplied by the
R4
300k
N1
MMFT3055VL
L1
100 H
MBRS0540
D1
100pF
2.2M
R5
C6
OUT
DD
and use the typical boost topology shown
should be greater than 1.1 (V
C5
22 F
OUT
Negative Output Voltage
Positive Output Voltage
> 1.1V
R6
56k
R7
56k
BATT
BATT
). If a larger negative
OUT
Q1
MMBT2907
OPTIONAL
. To use the alter-
must be limited
BATT
12.5V
TO
23.5V OUT
VOUTSW
).