MAX1896EUT#TG16 Maxim Integrated Products, MAX1896EUT#TG16 Datasheet - Page 6

• Manufacturer Part Number: MAX1896EUT#TG16
• Description: IC DC-DC CONV STEP UP SOT23-6
• Manufacturer: Maxim Integrated Products
• Type: Step-Up (Boost)r

Specifications of MAX1896EUT#TG16

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.6 ~ 13 V
• Current - Output: 500mA
• Frequency - Switching: 1.4MHz
• Voltage - Input: 2.6 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Power - Output: 727mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
The MAX1896 is a highly efficient power supply that
employs a current-mode, fixed-frequency pulse-width
modulation (PWM) architecture for fast-transient response
and low-noise operation. The functional diagram is shown
in Figure 2. As the load varies, the error amplifier sets the
inductor peak current necessary to supply the load and
regulate the output voltage. To maintain stability at high
duty cycle, a slope-compensation signal is internally
summed with the current-sense signal.
At light loads, this architecture allows the MAX1896 to
skip cycles to prevent overcharging the output voltage.
In this region of operation, the inductor ramps up to a
peak value of about 100mA, discharges to the output
and waits until another pulse is needed again.
The output-current capability of the MAX1896 is a func-
tion of current limit, input voltage, and inductor value.
Because of the slope compensation used to stabilize
the feedback loop, the duty cycle affects the current
limit. The output-current capability is governed by the
following equation:
where:
I
Characteristics)
V
f
L = inductor value, (H)
η = conversion efficiency, 0.85 nominal
V
V
6
LIM
OSC
DIODE
IN
OUT
I




OUT MAX
(
x
_______________________________________________________________________________________
= input voltage, (V)
I
LIM x
= current limit specified at 50% (see Electrical
= oscillator frequency, (Hz)
η
= output voltage, (V)
(
= catch diode forward drop at I
x
( .
V
1 45
)
DUTY
V
V
OUT
IN
OUT
=
−
V
OUT
0 9
.
−
=
I
LIM
x Duty
DUTY CYCLE
Output-Current Capability
−
Detailed Description
V
x R
IN
))
+
ON
−



V
DIODE
0 5
+
.
V
×
f
DIODE
OSC x L
=
Duty x V
LIM
, (V)
IN







The MAX1896 can be programmed for soft-start upon
power-up with an external capacitor. When the
MAX1896 is turned on, the soft-start capacitor (C
charged at a constant current of 4µA, ramping up to
0.5V. During this time, the SS voltage directly controls
the peak-inductor current, allowing 0A at V
the full current limit at V
current is available after the soft-start cycle is complet-
ed. When the MAX1896 is turned off, the soft-start
capacitor is internally discharged to ground.
The MAX1896 shuts down to reduce the supply current
to 0.01µA when SHDN is low. In this mode, the internal
reference, error amplifier, comparators, biasing circuit,
and N-channel MOSFET are turned off. The step-up
converter’s output is still connected to IN via the exter-
nal inductor and output rectifier.
The MAX1896 operates well with a variety of external
components. The components in Figure 1 are suitable
for most applications. See the following sections to opti-
mize external components for a particular application.
Inductor selection depends on input voltage, output volt-
age, maximum current, size, and availability of inductor
values. Other factors can include efficiency and ripple
voltage. Inductors are specified by their inductance (L),
peak current (I
step-up circuit equations are useful in choosing the
inductor values based on the application. They allow the
trading of peak current and inductor value while consid-
ering component availability and cost.
The equation used here assumes a constant LIR, which
is the ratio of the inductor peak-to-peak AC current to
average DC inductor current. A good compromise
between the size of the inductor versus loss and output
ripple is to choose an LIR of 0.3 to 0.5. The peak induc-
tor current is then given by:
where:
I
V
OUT(MAX)
IN(MIN)
I
PK
= minimum input voltage, (V)
=
= maximum output current, (A)



I
OUT MAX
PK
Applications Information
η
), and resistance (R
(
x V
)
IN MIN
SS
(
x V
= 1.5V. The maximum load
OUT
)
Inductor Selection



x



1
L
). The following
+
Shutdown
Soft-Start
LIR
SS
2
= 0.5V to



SS
) is