Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1:
LX has internal clamp diodes to IN and GND. Applications that forward bias these diodes should not exceed the IC’s package
power-dissipation limit.
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= 3.6V,
SHDN
= IN, T
A
= -40°C to +85°C, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
Supply Range
UVLO Threshold
Supply Current
Output Voltage Range
Output Voltage Accuracy
(Falling Edge)
Output Load Regulation
(Voltage Positioning)
SHDN
Logic Input Level
SHDN
Input Bias Current
Minimum Required
SHDN
Reset
Time
Peak Current Limit
Valley Current Limit
Rectifier Off-Current Threshold
On-Resistance
LX Leakage Current
Minimum On and Off Times
Thermal Shutdown
Thermal-Shutdown Hysteresis
V
IH
V
IL
I
IH,IL
t
SHDN
I
LIMP
I
LIMN
I
LXOFF
R
ONP
R
ONN
I
LXLKG
t
ON(MIN)
t
OFF(MIN)
pFET switch
nFET rectifier
nFET rectifier
pFET switch, I
LX
= -40mA
nFET rectifier, I
LX
= 40mA
V
IN
= 5.5V, LX = GND
to IN,
SHDN
= GND
T
A
= +25°C
T
A
= +85°C
SYMBOL
V
IN
UVLO
I
CC
V
OUT
V
IN
rising, 100mV hysteresis
No load, no switching
SHDN
= GND
Factory preset
I
LOAD
= 0mA, T
A
= +25°C
I
LOAD
= 0mA, T
A
= -40°C to +85°C
Equal to inductor DC resistance
V
IN
= 2.7V to 5.5V
V
IN
= 2.7V to 5.5V
V
IN
= 5.5V,
SHDN
= GND or IN
T
A
= +25°C
T
A
= +85°C
10
590
450
10
770
650
40
0.6
0.35
0.1
1
95
95
+160
20
1400
1300
70
1.2
0.7
1
0.001
0.01
1.4
0.4
1
T
A
= +25°C
T
A
= +85°C
0.8
-1
-2
R
L
0
CONDITIONS
MIN
2.7
2.44
2.6
28
0.01
0.1
2.5
+1
+2
V
%
V/A
V
µA
µs
mA
mA
mA
Ω
µA
ns
°C
°C
TYP
MAX
5.5
2.70
48
0.1
µA
UNITS
V
V
Note 2:
All devices are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed by design.
2
Maxim Integrated
MAX8640Y/MAX8640Z
Tiny 500mA, 4MHz/2MHz Synchronous
Step-Down DC-DC Converters
Typical Operating Characteristics
(V
IN
= 3.6V, V
OUT
= 1.5V, MAX8640Z, L = Murata LQH32CN series, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
1.8V OUTPUT
MAX8640Y/Z toc01
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX8640YEXT18
MAX8640Y/Z toc02
SWITCHING FREQUENCY
vs. LOAD CURRENT
MAX8640ZEXT15
SWITCHING FREQUENCY (MHz)
MAX8640Y/Z toc03
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
MAX8640YEXT18
35
30
SUPPLY CURRENT (μA)
25
20
15
10
5
10
MAX8640ZEXT15
1
MAX8640YEXT18
0.1
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
0
100
SUPPLY VOLTAGE (V)
200
300
400
LOAD CURRENT (mA)
500
1000
OUTPUT VOLTAGE vs. LOAD CURRENT
(VOLTAGE POSITIONING)
MAX8640Y/Z toc04
LIGHT-LOAD SWITCHING WAVEFORMS
(I
OUT
= 1mA)
V
OUT
1.55
MAX8640ZEXT15
1.50
OUTPUT VOLTAGE (V)
MAX8640Y/Z toc05
20mV/div
(AC-COUPLED)
1.45
V
LX
1.40
2V/div
1.35
I
LX
200mA/div
1.30
0
100
200
300
400
LOAD CURRENT (mA)
500
10μs/div
MEDIUM-LOAD SWITCHING WAVEFORMS
(I
OUT
= 40mA)
MAX8640Y/Z toc06
HEAVY-LOAD SWITCHING WAVEFORMS
(I
OUT
= 300mA)
MAX8640Y/Z toc07
V
OUT
20mV/div
(AC-COUPLED)
V
OUT
20mV/div
(AC-COUPLED)
2V/div
V
LX
2V/div
0V
200mA/div
0mA
200ns/div
V
LX
0V
200mA/div
I
LX
I
LX
0mA
200ns/div
Maxim Integrated
3
MAX8640Y/MAX8640Z
Tiny 500mA, 4MHz/2MHz Synchronous
Step-Down DC-DC Converters
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, V
OUT
= 1.5V, MAX8640Z, L = Murata LQH32CN series, T
A
= +25°C, unless otherwise noted.)
LIGHT-LOAD STARTUP WAVEFORM
(100Ω LOAD)
MAX8640Y/Z toc08
HEAVY-LOAD STARTUP WAVEFORM
(5Ω LOAD)
MAX8640Y/Z toc09
V
SHDN
5V/div
1V/div
V
SHDN
5V/div
1V/div
V
OUT
0V
100mA/div
V
OUT
0V
100mA/div
I
IN
0mA
500mA/div
I
IN
I
LX
0mA
500mA/div
0mA
I
LX
0mA
20μs/div
20μs/div
LINE-TRANSIENT RESPONSE
(4V TO 3.5V TO 4V)
MAX8640Y/Z toc10
LOAD-TRANSIENT RESPONSE
(5mA TO 250mA TO 5mA)
MAX8640Y/Z toc11
V
IN
1V/div
4V
V
OUT
50m/div
AC-COUPLED
V
OUT
20mV/div
AC-COUPLED
I
LX
500mA/div
200mA/div
I
LX
200mA/div
0mA
20μs/div
40μs/div
I
OUT
0mA
LOAD-TRANSIENT RESPONSE
(10mA TO 500mA TO 10mA)
MAX8640Y/Z toc12
V
OUT
100mV/div
AC-COUPLED
500mA/div
0V
I
LX
I
OUT
200mA/div
40μs/div
4
Maxim Integrated
MAX8640Y/MAX8640Z
Tiny 500mA, 4MHz/2MHz Synchronous
Step-Down DC-DC Converters
Pin Description
PIN
1
2, 5
3
NAME
LX
GND
OUT
FUNCTION
Inductor Connection to the Internal Drains of the p-channel and n-channel MOSFETs. High impedance
during shutdown.
Ground. Connect these pins together directly under the IC.
Output Sense Input. Bypass with a ceramic capacitor as close as possible to pin 3 (OUT) and pin 2 (GND).
OUT is internally connected to the internal feedback network.
Active-Low Shutdown Input. A logic-low on
SHDN
disables the step-down DC-DC and resets the logic. A logic-
high on
SHDN
enables the step-down DC-DC. Ensure that
SHDN
is low for
≥
10µs (t
SHDN
) after V
IN
rises above its
undervoltage lockout threshold (UVLO) to reset the logic. See the
Shutdown Mode
section for more information.
Supply Voltage Input. Input voltage range is 2.7V to 5.5V. Bypass with a ceramic capacitor as close as
possible to pin 6 (IN) and pin 5 (GND).
4
SHDN
6
IN
Detailed Description
The MAX8640Y/MAX8640Z step-down converters deliv-
er over 500mA to outputs from 0.8V to 2.5V. They utilize
a proprietary hysteretic PWM control scheme that
switches at up to 4MHz (MAX8640Z) or 2MHz
(MAX8640Y), allowing some trade-off between efficien-
cy and size of external components. At loads below
100mA, the MAX8640Y/MAX8640Z automatically switch
to pulse-skipping mode to minimize the typical quies-
cent current (28µA). Output ripple remains low at all
loads, while the skip-mode switching frequency
remains ultrasonic down to 1mA (typ) loads. Figure 1 is
the simplified functional diagram.
Voltage-Positioning Load Regulation
The MAX8640Y/MAX8640Z utilize a unique feedback
network. By taking DC feedback from the LX node, the
usual phase lag due to the output capacitor is
removed, making the loop exceedingly stable and
allowing the use of very small ceramic output capacitors.
This configuration yields load regulation equal to the
inductor’s series resistance multiplied by the load current.
This voltage-positioning load regulation greatly reduces
overshoot during load transients, effectively halving the
peak-to-peak output-voltage excursions compared to tra-
ditional step-down converters. See the Load-Transient
Response in the
Typical Operating Characteristics.
Control Scheme
A proprietary hysteretic PWM control scheme ensures
high efficiency, fast switching, fast transient response,
low output ripple, and physically tiny external compo-
nents. This control scheme is simple: when the output
voltage is below the regulation threshold, the error
comparator begins a switching cycle by turning on the
high-side switch. This switch remains on until the mini-
mum on-time expires and the output voltage is above
the regulation threshold or the inductor current is above
the current-limit threshold. Once off, the high-side
switch remains off until the minimum off-time expires
and the output voltage falls again below the regulation
threshold. During the off period, the low-side synchro-
nous rectifier turns on and remains on until either the
high-side switch turns on again or the inductor current
approaches zero. The internal synchronous rectifier
eliminates the need for an external Schottky diode.
Shutdown Mode
A logic-low on
SHDN
places the MAX8640Y/MAX8640Z
in shutdown mode by disabling the step-down DC-DC
and resetting its logic. In shutdown mode, the supply
current (I
CC
) is reduced to 0.01µA typical. Additionally,
the power MOSFETs between IN, LX, and GND
(Figure 1) are open such that LX is high impedance.
Ensure that
SHDN
is low for
≥
10µs (t
SHDN
) after V
IN
rises above its undervoltage lockout threshold (UVLO)
to reset the logic. In the majority of systems, this t
SHDN
requirement is fulfilled naturally because the upstream
logic controlling
SHDN
is powered off of the same V
IN
as the MAX8640Y/MAX8640Z. However, systems that
want an always on regulator without the burden of
enable/disable logic can use an R and C circuit on
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