MAX1747EUP Maxim Integrated Products, MAX1747EUP Datasheet - Page 10

• Manufacturer Part Number: MAX1747EUP
• Description: Charge Pumps
• Manufacturer: Maxim Integrated Products

Specifications of MAX1747EUP

• Function: Step Up, Step Down
• Output Voltage: 4.5 V to 5.5 V, +/- 35 V
• Output Current: 200 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: TSSOP-20
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Triple Charge-Pump TFT LCD
DC-DC Converter
Figure 2. Main Charge-Pump Block Diagram
During the first half-cycle, the P-channel MOSFET turns
on, and flying capacitor C5 charges to V
diode drop (Figure 3). During the second half-cycle,
the P-channel MOSFET turns off, and the N-channel
MOSFET turns on, level shifting C5. This connects C5 in
parallel with the reservoir capacitor, C6. If the voltage
across C6 minus a diode drop is lower than the voltage
across C5, current flows from C5 to C6 until the diode
(D4) turns off. The amount of charge transferred to the
output is controlled by the variable N-channel R
During the first half-cycle, the N-channel MOSFET turns
on and charges the flying capacitor, C3 (Figure 4). This
initial charge is controlled by the variable N-channel
R
MOSFET turns off, and the P-channel MOSFET turns
on, level shifting C3 by V
in parallel with the reservoir capacitor, C4. If the voltage
across C4 plus a diode drop (V
er than the level-shifted flying capacitor voltage (V
V
turns off.
The shutdown pin (SHDN) on the MAX1747 performs a
dual function: it shuts down the device and determines
the oscillator frequency. The SHDN input looks like a
diode to ground and should be driven through a resis-
tor (Figure 5).
10
C
SUPP
ON
INTG
. During the second half-cycle, the N-channel
______________________________________________________________________________________
), charge flows from C3 to C4 until the diode (D2)
INTG
MAX1747
Frequency Selection and Shutdown
PGND
OSC
V
1.25V
gm
REF
SUPP
SUPM
Negative Charge Pump
POS
Positive Charge Pump
volts. This connects C3
GND
CXN
CXP
OUT
REF
V
V
FB
OUT
REF
= 1.25V
= [1+ (R1/R2)]
+ V
DIODE
C
V
2.7V TO 4.5V
CX
REF
SUPM
C1
SUPN
✕
= V
V
) is small-
R1
R2
REF
IN
V
ON
minus a
OUT
.
C
C3
OUT
+
Driving SHDN low forces all three MAX1747 converters
into shutdown mode. When disabled, the supply cur-
rent drops to 20µA (max) to maximize battery life, and
OUT is pulled to ground through an internal 10Ω resis-
tor. For the low-power charge pumps, the output
capacitance and load current determine the rate at
which each output voltage will decay. The device acti-
vates (see Power-up Sequencing) once SHDN is for-
ward biased (minimum of 3µA of current). Do not leave
SHDN floating. For a typical application where shut-
down is used only to set the switching frequency, con-
nect SHDN to the input (V
resistor for a 1MHz switching frequency.
The bias current into SHDN, programmed with an exter-
nal resistor, determines the oscillator frequency (see
Typical Operating Characteristics). To select the fre-
quency, calculate the external resistor value, R
using the following formula:
where R
frequency in the 200kHz to 2MHz range. This frequen-
cy range corresponds to SHDN input currents between
3µA to 65µA. Proper operation of the oscillator is not
guaranteed beyond these limits. Forcing SHDN below
400mV disables the device.
For the MAX1747, soft-start is achieved by controlling
the rise rate of the output voltage, regardless of output
capacitance or output load, and limited only by the out-
put impedance of the regulator (see Startup Waveforms
Figure 3. Negative Charge-Pump Block Diagram
R
FREQ
MAX1747
OSC
FREQ
GND
= 45.5 (MHz / mA)
is in kΩ and f
V
1.25V
REF
PGND
SUPN
DRVN
FBN
REF
OSC
IN
✕
C5
= 3.3V) with a 120kΩ
(V
is in MHz. Program the
ON
R6
C
V
V
V
REF
R5
NEG
REF
– 0.7V) / f
SUPP
D3
D4
= 1.25V
= -(R5/R6)
= 2.7V TO 13V
Soft-Start
✕
C6
V
OSC
NEG
V
REF
FREQ
,