Rainbow Electronics MAX16904 User Manual

General Description
The MAX16904 is a small, synchronous buck converter with integrated high-side and low-side switches. The device is designed to deliver 600mA with input voltages from +3.5V to +28V while using only 25µA quiescent current at no load. Voltage quality can be monitored by observing the PGOOD signal. The MAX16904 can oper­ate in dropout by running at 97% duty cycle, making it ideal for automotive and industrial applications.
The MAX16904 operates at a 2.1MHz frequency, allow­ing for small external components and reduced output ripple. It guarantees no AM band interference. SYNC input programmability enables three frequency modes for optimized performance: forced fixed-frequency operation, SKIP mode (ultra-low quiescent current of 25µA), and synchronization to an external clock. The MAX16904 can be ordered with spread-spectrum fre­quency modulation, designed to minimize EMI-radiated emissions due to the modulation frequency.
The MAX16904 is available in a thermally enhanced, 3mm x 3mm, 10-pin TDFN package or a 16-pin TSSOP package. The MAX16904 operates over the -40°C to +125°C automotive temperature range.
Applications
Automotive
Industrial
Military
High-Voltage Input-Power DC-DC Applications
Features
o Wide +3.5V to +28V Input Voltage Range
o Tolerates Input Voltage Transients to +42V
o 600mA Minimum Output Current with Overcurrent
Protection
o Fixed Output Voltages (+3.3V and +5V)
o 2.1MHz Switching Frequency with Three Modes of
Operation
25µA Ultra-Low Quiescent Current SKIP Mode Forced Fixed-Frequency Operation External Frequency Synchronization
o Optional Spread-Spectrum Frequency Modulation
o Power-Good Output
o Enable-Pin Compatible from +3.3V Logic Level to
+42V
o Thermal Shutdown Protection
o -40°C to +125°C Automotive Temperature Range
o 10-Pin TDFN-EP or 16-Pin TSSOP-EP Packages
o AEC-Q100 Qualified
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
________________________________________________________________
Maxim Integrated Products
1
19-5481; Rev 1; 11/10
EVALUATION KIT
AVAILABLE
PART
SPREAD
SPECTRUM
TEMP
RANGE
PIN­PACKAGE
MAX16904RATB__/V+ Disabled
-40°C to +125°C
10 TDFN-EP*
MAX16904RAUE__/V+ Disabled
-40°C to +125°C
16 TSSOP-EP*
MAX16904SATB__/V+ Enabled
-40°C to +125°C
10 TDFN-EP*
MAX16904SAUE__/V+ Enabled
-40°C to +125°C
16 TSSOP-EP*
Ordering Information
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Note: Insert the desired suffix letters (from
Selector Guide
) into the blanks to indicate the output voltage. Alternative output volt­ages available upon request.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*
EP = Exposed pad.
Selector Guide appears at end of data sheet.
MAX16904
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
2 _______________________________________________________________________________________
Typical Operating Circuits
5V AT 600mA
3.3V AT 600mA
10μF
10μF
4.7μH
3.3μH
4.7μF
0.1μF
4.7μF
0.1μF
SUP
EN
33kΩ
*
V
BAT
SIGNAL
LEVEL
MAX16904_50/V+
SYNC
BST
LX
PGND
OUTS
SUP
*
GND
PGOOD
BIAS
20kΩ
2.2μF
EN
33kΩ
V
BAT
SIGNAL
LEVEL
MAX16904_33/V+
SYNC
BST
LX
PGND
OUTS
GND
PGOOD
20kΩ
BIAS
2.2μF
*PLACE INPUT SUPPLY CAPACITORS AS CLOSE AS POSSIBLE TO THE SUP PIN. SEE THE APPLICATIONS INFORMATION SECTION FOR MORE DETAILS.
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
_______________________________________________________________________________________ 3
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
SUP
= +14V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C, unless otherwise noted.)
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.
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial
.
(Voltages referenced to GND.)
SUP, EN..................................................................-0.3V to +42V
BST to LX..................................................................-0.3V to +6V
LX..............................................................-0.3V to (V
SUP
+ 0.3V)
BST .........................................................................-0.3V to +47V
OUTS ......................................................................-0.3V to +12V
SYNC, PGOOD, BIAS............................................-0.3V to +6.0V
PGND to GND .......................................................-0.3V to +0.3V
LX Continuous RMS Current .................................................1.0A
OUTS Short-Circuit Duration ......................................Continuous
ESD Protection
Human Body Model .........................................................±2kV
Machine Model ..............................................................±200V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin TDFN (derate 24.4 mW/°C above +70°C) ..........1951mW
16-Pin TSSOP (derate 26.1 mW/°C above +70°C) ........2089mW
Junction-to-Case Thermal Resistance (θ
JC
) (Note 1)
10-Pin TDFN...................................................................9°C/W
16-Pin TSSOP.................................................................3°C/W
Junction-to-Ambient Thermal Resistance (θ
JA
) (Note 1)
10-Pin TDFN.................................................................41°C/W
16-Pin TSSOP............................................................38.3°C/W
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range V
Supply Current I
UV Lockout
Bias Voltage V
Bias Current Limit I
BUCK CONVERTER
Voltage Accuracy
V
UVLO,HYS
V
V
V
V
SUP
SUP
V
UVLO
BIAS
BIAS
OUT,5V
OUT,3.3V
OUT,5V
OUT,3.3V
(Note 2) 3.5 28
t < 1s 42
EN = low 4 8
EN = high, no load 25 35
EN = high, continuous, no switching 1 mA
Bias rising 2.8 3 3.2
Hysteresi s 0.4
+5.5V  V
10 mA
V
= 5V, fixed frequency -2.0% 5 +2.5%
OUT
V
= 5V, SKIP mode
OUT
(Note 3)
V
= 3.3V, fixed frequency -2.0% 3.3 +2.5%
OUT
V
= 3.3V, SKIP mode
OUT
(Note 3)
V
= 5V, fixed frequency -3.0% 5 +2.5%
OUT
V
= 5V, SKIP mode
OUT
(Note 3)
V
= 3.3V, fixed frequency
OUT
V
= 3.3V, SKIP mode
OUT
(Note 3)
 +42V 5 V
SUP
6.5V V I
LOAD
= 0°C to +125°C
T
A
6.5V V I
LOAD
= -40°C to
T
A
+125°C
18V,
SUP
= 0 to 600mA,
18V,
SUP
= 0 to 600mA,
-2.0% 5 +4%
-2.0% 3.3 +4%
-3.0%
-3.0%
-3.0%
5 +4%
3.3 +2.5%
3.3 +4%
V
μA
V
V
MAX16904
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V
SUP
= +14V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C, unless otherwise noted.)
Note 2: When the typical minimum on-time of 80ns is violated, the device skips pulses. Note 3: Not production tested. Guaranteed by design.
SKIP-Mode Peak Current I
High-Side DMOS RDSON R
Low-Side DMOS RDSON R
DMOS Peak Current-Limit Threshold
Soft-Start Ramp Time t
LX Ri se Time t
Minimum On-Time tON 80 ns
PWM Switching Frequency fSW Internally generated 1.925 2.1 2.275 MHz
SYNC Input Frequency Range f
Spread-Spectrum Range SS Spread-spectrum option on ly +6 %
PGOOD
PGOOD Threshold
PGOOD Debounce t
PGOOD High Leakage Current I
PGOOD Output Low Level V
LOGIC L E V ELS
EN Le vel
EN Input Current I
SYNC Switching Threshold
SYNC Internal Pulldown R
THERMAL PROTECTION
Thermal Shutdown T
Thermal Shutdown Hysteresis T
PARAMETER S YMBOL CONDITIONS MIN TYP MAX UNITS
SKIP
V
ON,HS
250 450 m
ON,LS
I
MAX
SS
5 ns
RISE,LX
1.8 2.6 MHz
SYNC
V
V
LEAK,PGD
OUT,PGD
V
V
PD,SYNC
SHDN,HYS
V
THR,P GD
V
THF,PGD
10 μs
DEB
TA = +25°C 1 μA
Sinking 1mA 0.4 V
V
2.4
IH,EN
0.6
V
IL, EN
VEN = V
IN,EN
1.4
IH,SYNC
0.4
IL, SYNC
200 k
175 °C
SHDN
= 5V 400 800 m
BIAS
ris ing 93
OUT
falling 88 91 94
OUT
= +42V, TA = +25°C 1 μA
SUP
15 °C
350 mA
850 1500 1725 mA
7 8 9 ms
%
V
V
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(V
SUP
= +14V, TA= +25°C, unless otherwise noted.)
EFFICIENCY
vs. LOAD CURRENT
100
90
80
SKIP MODE
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.00001 1
FFF MODE
I
(A)
LOAD
0.10.010.0010.0001
LOAD REGULATION
4
3
2
1
0
-1
-2
OUTPUT-VOLTAGE CHANGE (%)
-3
-4 0 0.6
SKIP MODE
FFF MODE
0.50.40.1 0.2 0.3
LOAD CURRENT (A)
MAX16904 toc01
MAX16904 toc04
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE (SKIP MODE)
60
50
40
30
20
SUPPLY CURRENT (µA)
10
0
628
5V PART
3.3V PART
INPUT VOLTAGE (V)
MAX16904 toc02
2624222018161412108
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
15
12
9
6
SUPPLY CURRENT (µA)
3
0
628
INPUT VOLTAGE (V)
MAX16904 toc05
2624222018161412108
4
3
2
1
0
-1
-2
OUTPUT VOLTAGE CHANGE (%)
-3
-4 628
STARTUP WAVEFORM (I
LINE REGULATION
= 600mA)
(I
LOAD
INPUT VOLTAGE (V)
LOAD
1ms/div
26248 10 12 16 18 2014 22
= 600mA)
MAX16904 toc06
MAX16904 toc03
EN 5V/div
I
INDUCTOR
0.5A/div
PGOOD 5V/div
V
OUT
5V/div
SHUTDOWN WAVEFORM (I
20µs/div
LOAD
= 600mA)
MAX16904 toc07
EN 5V/div
I
INDUCTOR
0.5A/div
PGOOD 5V/div
V
OUT
5V/div
(FIXED MODE)
5V
5V
I
= 100mA TO 600mA TO 100mA
LOAD
200μs/div
MAX16904 toc08
I
LOAD
500mA/div
V
OUT
200mV/div AC-COUPLED
PGOOD 5V/div
LOAD TRANSIENT RESPONSE
MAX16904
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V
SUP
= +14V, TA= +25°C, unless otherwise noted.)
Pin Description
Pin Configurations
LOAD TRANSIENT RESPONSE
(SKIP MODE)
5V
5V
I
= 100mA TO 600mA TO 100mA
LOAD
200μs/div
MAX16904 toc09
TOP VIEW
I
LOAD
500mA/div
V
OUT
200mV/div AC-COUPLED
PGOOD 5V/div
UNDERVOLTAGE PULSE (COLD CRANK)
14V
3.5V
10ms/div
I
LOAD
MAX16904 toc10
= 500mA
V
SUP
10V/div
V
OUT
5V/div
PGOOD 5V/div
I
LOAD
1A/div
STANDBY CURRENT
vs. LOAD CURRENT
300
250
200
(μA)
150
IN
I
100
50
0
0.01 1 I
LOAD
0.1 (mA)
MAX16904 toc11
+
1
2
3
4
MAX16904
5
6 11PGND PGOOD
7
8 9OUTS N.C.
PIN
TDFN-EP TSSOP-EP
+
1
2
MAX16904
3
4
5 6OUTS PGOOD
10BST EN
9SUP GND
8LX BIAS
7PGND SYNC
EP
TDFN
NAME FUNCTION
1 1 BST Boot strap Capacitor for High-Side Driver (0.1μF)
Voltage Supply Input. Connect a 4.7μF ceramic capacitor from SUP to PGND. Place
2 2, 3 SUP
the capacitor very close to the SUP pin. For the TSSOP-EP package, connect both SUP pins t ogether for proper operat ion.
3 4, 5 LX
4 6, 7 PGND
Buck Switching Node. LX is high impedance when the device is off. For the TSSOP package, connect both LX pins together for proper operation.
Power Ground. For the TSSOP-EP package, connect both PGND pins together for proper operation.
16BST N.C.
15SUP EN
14SUP GND
13LX BIAS
12LX SYNC
10PGND N.C.
EP
TSSOP
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
_______________________________________________________________________________________ 7
Pin Description (continued)
Functional Diagram
PIN
TDFN-EP TSSOP-EP
5 8 OUTS
6 11 PGOOD
7 12 SYNC
8 13 BIAS +5V Internal Logic Supply. Connect a 2.2μF ceramic capacitor from BIAS to GND.
9 14 GND Analog Ground
10 15 EN Enable Input. EN is high-voltage compatible. Drive EN HIGH for normal operation.
9, 10, 16 N.C. No Connection. Not internally connected.
 EP Exposed Pad. Connect EP to PGND. Do not use EP as the only ground connection.
NAME FUNCTION
Buc k Regulator Voltage-Sense Input. Bypass OUTS to PGND with a 10μF or larger X7R ceramic capacitor.
Open-Drain Power-Good Output. External pullup resistor required for automat ic SKIP mode operation.
Sync Input. SYNC allows the device to synchronize to other supplies. When connected to GND or unconnected, SKIP mode is enabled under light loads. When connected to a clock source or BIAS, forced PWM mode is enabled.
SYNC
REF
OSCBANDGAP
CLK
BST
SUP
BIAS
EN
HVLDO
CURRENT-SENSE
SOFT-START
OUTS
EAMP
V
COMP
GOOD
PGOOD
AND
SLOPE COMPENSATION
PWM
LOGIC
CONTROL
MAX16904
GND
HSD
LX
BIAS
LSD
PGND
MAX16904
Detailed Description
The MAX16904 is a small, current-mode buck converter that features synchronous rectification and requires no external compensation network. The device is designed for 600mA output current, and can stay in dropout by running at 97% duty cycle. It provides an accurate out­put voltage within the +6.5V to +18V input range. Voltage quality can be monitored by observing the PGOOD signal. The device operates at 2.1MHz (typ) frequency, which allows for small external components, reduced output ripple, and guarantees no AM band interference.
The device features an ultra-low 25μA (typ) quiescent supply current in standby mode. Standby mode is entered when load currents are below 5mA and when SYNC is low. The device operates from a +3.5V to +28V supply voltage and tolerates transients up to +42V, making it ideal for automotive applications. The device is available in factory-trimmed output voltages from 1.8V to 10.7V in 100mV steps. Contact the factory for availability of voltage options.
Enable (EN)
The device is activated by driving EN high. EN is com­patible from a +3.3V logic level to automotive battery levels. EN can be controlled by microcontrollers and automotive KEY or CAN inhibit signals. The EN input has no internal pullup/pulldown current to minimize overall quiescent supply current. To realize a program­mable undervoltage lockout level, use a resistor­divider from SUP to EN to GND.
BIAS/UVLO
The device features undervoltage lockout. When the device is enabled, an internal bias generator turns on. LX begins switching after V
BIAS
has exceeded the inter-
nal undervoltage lockout level V
UVLO
= 3V (typ).
Soft-Start
The device features an internal soft-start timer. The out­put voltage soft-start ramp time is 8ms (typ). If a short circuit or undervoltage is encountered, after the soft­start timer has expired, the device is disabled for 30ms (typ) and it reattempts soft-start again. This pattern repeats until the short circuit has been removed.
Oscillator/Synchronization and
Efficiency (SYNC)
The device has an on-chip oscillator that provides a switching frequency of 2.1MHz (typ). Depending on the condition of SYNC, two operation modes exist. If SYNC is unconnected or at GND, the device must operate in highly efficient pulse-skipping mode if the load current is below the SKIP mode current threshold. If SYNC is at
BIAS or has a frequency applied to it, the device is in forced PWM mode. The device offers the best of both worlds. The device can be switched during operation between forced PWM mode and SKIP mode by switch­ing SYNC.
SKIP Mode Operation
SKIP mode is entered when the SYNC pin is connected to ground or is unconnected and the peak load current is < 400mA (typ). In this mode, the high-side FET is turned on until the current in the inductor is ramped up to 400mA (typ) peak value and the internal feedback voltage is above the regulation voltage (1.2V typ). At this point, both the high-side and low-side FETs are turned off. Depending on the choice of the output capacitor and the load current the high-side FET turns on when OUTS (valley) drops below the 1.2V (typ) feed­back voltage.
Achieving High Efficiency at Light Loads
The device operates with very low quiescent current at light loads to enhance efficiency and conserve battery life. When the device enters SKIP mode the output cur­rent is monitored to adjust the quiescent current.
When the output current is < 5mA, the device operates in the lowest quiescent current mode also called the stand­by mode. In this mode, the majority of the internal circuit­ry (excluding that necessary to maintain regulation) in the device, including the internal high-voltage LDO, is turned off to save current. Under no load and with SKIP mode enabled, the device draws only 25μA (typ) current. For load currents > 5mA, the device enters normal SKIP mode while still maintaining very high efficiency.
Controlled EMI with Forced-Fixed Frequency
In forced PWM mode, the device attempts to operate at a constant switching frequency for all load currents. For tightest frequency control, apply the operating frequen­cy to SYNC. The advantage of this mode is a constant switching frequency, which improves EMI performance; the disadvantage is that considerable current can be thrown away. If the load current during a switching cycle is less than the current flowing through the induc­tor, the excess current is diverted to GND. With no external load present, the operating current is in the 10mA range.
Extended Input Voltage Range
In some cases, the device is forced to deviate from its operating frequency independent of the state of SYNC. For input voltages above 18V, the required duty cycle to regulate its output may be smaller than the minimum on-time (80ns, typ). In this event, the device is forced to lower its switching frequency by skipping pulses.
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
8 _______________________________________________________________________________________
If the input voltage is reduced and the device approaches dropout, it tries to turn on the high-side FET continuously. To maintain gate charge on the high­side FET, the BST capacitor must be periodically recharged. To ensure proper charge on the BST capacitor when in dropout, the high-side FET is turned off every 6.5μs and the low-side FET is turned on for about 150ns. This gives an effective duty cycle of > 97% and a switching frequency of 150kHz when in dropout.
Spread-Spectrum Option
The device has an optional spread-spectrum version. If this option is selected, then the internal operating fre­quency varies by +6% relative to the internally generat­ed operating frequency of 2.1MHz (typ). Spread spectrum is offered to improve EMI performance of the device. By varying the frequency 6% only in the posi­tive direction, the device still guarantees that the
2.1MHz frequency does not drop into the AM band limit of 1.8MHz. Additionally, with the low minimum on-time of 80ns (typ) no pulse skipping is observed for a 5V output with 18V input maximum battery voltage in steady state.
The internal spread spectrum does not interfere with the external clock applied on the SYNC pin. It is active only when the device is running with internally generat­ed switching frequency.
Power-Good (PGOOD)
The device features an open-drain power-good output. PGOOD is an active-high output that pulls low when the output voltage is below 91% of its nominal value. The device is high impedance when the output voltage is above 93% of its nominal value. Connect a 20kΩ (typ) pullup resistor to an external supply or the on-chip BIAS output.
Overcurrent Protection
The device limits the peak output current to 1.5A (typ). The accuracy of the current limit is ±15%, which makes selection of external components very easy. To protect against short-circuit events, the device shuts off when OUTS is below 1.5V (typ) and one overcurrent event is detected. The device attempts a soft-start restart every 30ms and stays off if the short circuit has not been removed. When the current limit is no longer present, it reaches the output voltage by following the normal soft­start sequence. If the device die reaches the thermal limit of +175°C (typ) during the current-limit event, it immediately shuts off.
Thermal-Overload Protection
The device features thermal-overload protection. The device turns off when the junction temperature exceeds +175°C (typ). Once the device cools by 15°C (typ), it turns back on with a soft-start sequence.
Applications Information
Inductor Selection
Three key inductor parameters must be specified for operation with the device: inductance value (L), peak inductor current (I
PEAK
), and inductor saturation current
(I
SAT
). The minimum required inductance is a function of operating frequency, input-to-output voltage differen­tial, and the peak-to-peak inductor current (ΔI
P-P
). Higher ΔI
P-P
allows for a lower inductor value,
while a lower ΔI
P-P
requires a higher inductor value. A lower inductor value minimizes size and cost, improves large-signal and transient response, but reduces effi­ciency due to higher peak currents and higher peak-to­peak output-voltage ripple for the same output capacitor. On the other hand, higher inductance increases efficiency by reducing the ripple current. Resistive losses due to extra wire turns can exceed the benefit gained from lower ripple current levels especial­ly when the inductance is increased without also allow­ing for larger inductor dimensions. A good compromise is to choose ΔI
P-P
equal to 30% of the full load current.
Use the following equation to calculate the inductance:
VINand V
OUT
are typical values so that efficiency is optimum for typical conditions. The switching frequency is ~2.1MHz. The peak-to-peak inductor current, which reflects the peak-to-peak output ripple, is worse at the maximum input voltage. See the
Output Capacitor
sec­tion to verify that the worst-case output ripple is accept­able. The inductor saturation current is also important to avoid runaway current during continuous output short circuit. The output current may reach 1.725A since this is the maximum current limit. Choose an inductor with a saturation current of greater than 1.725A to ensure proper operation and avoid runaway.
Input Capacitor
The discontinuous input current of the buck converter causes large input ripple current. The switching frequen­cy, peak inductor current, and the allowable peak-to­peak input-voltage ripple dictate the input capacitance requirement. Increasing the switching frequency or the
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
_______________________________________________________________________________________ 9
()
VVV
OUT IN OUT
L
=
Vf I
IN SW P P
××
Δ
MAX16904
inductor value lowers the peak-to-average current ratio yielding a lower input capacitance requirement.
The input ripple comprises mainly of ΔVQ(caused by the capacitor discharge) and ΔV
ESR
(caused by the
ESR of the input capacitor). The total voltage ripple is the sum of ΔV
Q
and ΔV
ESR
. Assume the input-voltage ripple from the ESR and the capacitor discharge is equal to 50% each. The following equations show the ESR and capacitor requirement for a target voltage rip­ple at the input:
where:
and:
where I
OUT
is the output current, D is the duty cycle, and fSWis the switching frequency. Use additional input capacitance at lower input voltages to avoid pos­sible undershoot below the UVLO threshold during tran­sient loading.
Output Capacitor
The allowable output-voltage ripple and the maximum deviation of the output voltage during step load cur­rents determine the output capacitance and its ESR. The output ripple comprises of ΔVQ(caused by the capacitor discharge) and ΔV
ESR
(caused by the ESR of the output capacitor). Use low-ESR ceramic or alu­minum electrolytic capacitors at the output. For alu­minum electrolytic capacitors, the entire output ripple is contributed by ΔV
ESR
. Use the ESR
OUT
equation to cal­culate the ESR requirement and choose the capacitor accordingly. If using ceramic capacitors, assume the contribution to the output ripple voltage from the ESR and the capacitor discharge to be equal. The following equations show the output capacitance and ESR requirement for a specified output-voltage ripple.
where:
ΔI
P-P
is the peak-to-peak inductor current as calculated
above and f
SW
is the converter’s switching frequency. The allowable deviation of the output voltage during fast transient loads also determines the output capaci­tance and its ESR. The output capacitor supplies the step load current until the converter responds with a greater duty cycle. The response time (t
RESPONSE
) depends on the closed-loop bandwidth of the convert­er. The device’s high switching frequency allows for a higher closed-loop bandwidth, thus reducing t
RESPONSE
and the output capacitance requirement. The resistive drop across the output capacitor’s ESR and the capacitor discharge causes a voltage droop during a step load. Use a combination of low-ESR tan­talum and ceramic capacitors for better transient load and ripple/noise performance. Keep the maximum out­put-voltage deviations below the tolerable limits of the electronics being powered. When using a ceramic capacitor, assume an 80% and 20% contribution from the output capacitance discharge and the ESR drop, respectively. Use the following equations to calculate the required ESR and capacitance value:
where I
STEP
is the load step and t
RESPONSE
is the response time of the converter. The converter response time depends on the control-loop bandwidth.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching power losses and clean stable operation. Use a multilayer board wherever possible for better noise immunity. Refer to the MAX16904 Evaluation Kit for recommended PCB layout. Follow these guidelines for a good PCB layout:
1) The input capacitor (4.7μF, see the applications
schematic in the
Typical Operating Circuits
) should be placed right next to the SUP pins (pins 2 and 3 on the TSSOP-EP package). Because the device operates at
2.1MHz switching frequency, this placement is critical for effective decoupling of high-frequency noise from the SUP pins.
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
10 ______________________________________________________________________________________
ΔI
ESR
C
PP
IN
=
Δ
V
=
IDD
=
VV V
()
D
ESR
Δ
I
OUT
OUT
ΔVf
IN OUT OUT
Vf L
=
I
PP
+
×−
×
QSW
⎟ ⎠
2
1(
))
−× ××
IN SW
V
OUT
V
IN
ESR
C
=
OUT
Δ
V
ESR
=
Δ
I
PP
I
Δ
PP
Vf
Δ8
××
QSW
ΔI
PP
V
OUT RIPPLE
VV V
−×
()
IN OUT OUT
=
Vf L
IN SW
_
≅≅+ΔΔVV
××
ESR Q
V
Δ
ESR
=
I
STEP
×
V
Δ
Q
ESR
OUT
It
C
OUT
STEP RESPONSE
=
2) Solder the exposed pad to a large copper plane area under the device. To effectively use this copper area as heat exchanger between the PCB and ambi­ent, expose the copper area on the top and bottom side. Add a few small vias or one large via on the copper pad for efficient heat transfer. Connect the exposed pad to PGND ideally at the return terminal of the output capacitor.
3) Isolate the power components and high current paths from sensitive analog circuitry.
4) Keep the high current paths short, especially at the ground terminals. The practice is essential for stable jitter-free operation.
5) Connect the PGND and GND together preferably at the return terminal of the output capacitor. Do not connect them anywhere else.
6) Keep the power traces and load connections short. This practice is essential for high efficiency. Use thick copper PCB to enhance full load efficiency and power dissipation capability.
7) Route high-speed switching nodes away from sensi­tive analog areas. Use internal PCB layers as PGND to act as EMI shields to keep radiated noise away from the device and analog bypass capacitor.
ESD Protection
The device’s ESD tolerance is rated for Human Body Model and Machine Model. The Human Body Model discharge components are CS= 100pF and RD= 1.5kΩ (Figure 1). The Machine Model discharge components are CS= 200pF and RD= 0Ω (Figure 2).
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
______________________________________________________________________________________ 11
Figure 1. Human Body ESD Test Circuit
Figure 2. Machine Model ESD Test Circuit
R
D
HIGH-
VOLTAGE
DC
SOURCE
1MΩ
CHARGE-CURRENT-
LIMIT RESISTOR
C
100pF
S
1.5kΩ
DISCHARGE
RESISTANCE
STORAGE CAPACITOR
DEVICE UNDER
TEST
R
D
0Ω
HIGH-
VOLTAGE
DC
SOURCE
CHARGE-CURRENT-
LIMIT RESISTOR
200pF
C
S
DISCHARGE
RESISTANCE
STORAGE CAPACITOR
DEVICE UNDER
TEST
MAX16904
2.1MHz, High-Voltage, 600mA Mini-Buck Converter
12 ______________________________________________________________________________________
Chip Information
PROCESS: BiCMOS
Selector Guide
PART
OUTPUT VOLTAGE
(V)
PIN-PACKAGE
SPREAD-SPECTRUM
SWITCHING FREQUENCY
TOP
MAX16904RATB50/V+ 5
10 TDFN-EP*
AVY
MAX16904RAUE50/V+ 5
16 TSSOP-EP*
(5mm x 4.4mm)
⎯⎯
MAX16904SATB50/V+ 5
10 TDFN-EP*
Yes AWA
MAX16904SAUE50/V+ 5
16 TSSOP-EP*
(5mm x 4.4mm)
Yes
MAX16904RATB33/V+ 3.3
10 TDFN-EP*
AVX
MAX16904RAUE33/V+ 3.3
16 TSSOP-EP*
(5mm x 4.4mm)
⎯⎯
MAX16904SATB33/V+ 3.3
10 TDFN-EP*
Yes AVZ
MAX16904SAUE33/V+ 3.3
16 TSSOP-EP*
(5mm x 4.4mm)
Yes
MAX16904RAUE18/V+ 1.8
16 TSSOP-EP*
(5mm x 4.4mm)
⎯⎯
Note: All devices operate over the -40°C to +125°C automotive temperature range.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*
EP = Exposed pad.
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages
. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP T1033+1
21-0137 90-0003
16 TSSOP-EP U16E+3
21-0108 90-0120
(3mm x 3mm x 0.75mm)
MARK
(3mm x 3mm x 0.75mm)
(3mm x 3mm x 0.75mm)
(3mm x 3mm x 0.75mm)
MAX16904
2.1MHz, High-Voltage,
600mA Mini-Buck Converter
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
13
© 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION NUMBER
0 9/10 Initial release
1 11/10 Added new output voltage trim to Selector Guide 12
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
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