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AAT1232
24V 100mA Step-Up Converter General Description
The AAT1232 is a high frequency, high efficiency boost converter capable of 24V maximum output voltage. The internal power switch can deliver 100mA load current. It is the ideal power solution to power OLED, LCD, and CCD applications operating from a single cell lithium-ion battery. The high switching frequency (up to 2MHz) provides fast response to load transients with small external components. The fully integrated control IC simplifies the design while reducing the total PCB footprint. The AAT1232 offers a true load disconnect feature which isolates the load from the power source when EN/SET is pulled low. This eliminates leakage current and maintains zero voltage at the output while disabled. The output voltage can be dynamically set by activating one of two reference levels (FB1 or FB2) through the SEL logic pin. Optionally, AnalogicTech's Simple Serial ControlTM (S2CwireTM) interface provides dynamic programmability across a wide output voltage range through the EN/SET pin. The AAT1232 is available in a Pb-free, thermallyenhanced 16-pin 3x4mm TDFN low-profile package or a Pb-free 12-pin TSOPJW package.
Features
* * * * *
SwitchRegTM
* * * * * * * * * *
VIN Range: 2.7V to 5.5V Maximum Output: 24V @ 100mA True Load Disconnect Dynamic Voltage Control Options Hysteretic Control -- No External Compensation Components -- Excellent Load Transient Response -- High Efficiency at Light Load Up to 2MHz Switching Frequency Ultra-Small Inductor and Capacitors Integrated Low RDS(ON) MOSFET Switches Up to 85% Efficiency <1A Shutdown Current Integrated Soft Start Cycle-by-Cycle Current Limit Short-Circuit, Over-Temperature Protection Available in TSOPJW-12 or TDFN34-16 Package -40C to +85C Temperature Range
Applications
* * * * * * * CCD Bias Circuit Digital Still Cameras LCD Bias Circuit Mobile Handsets MP3 Players OLED Displays PDAs and Notebook PCs
Typical Application
L1 2.2H Input: 2.7V~5.5V C1 2.2F
VP VIN LIN
D1 Schottky
24V @ 100mA
AAT1232
SW PGND EN/SET FB2 SEL GND FB1
R1 576k
C2 2.2F, 25V
R2 10.0k R3 20.0k
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AAT1232
24V 100mA Step-Up Converter Pin Descriptions
Pin #
TSOPJW-12 TDFN34-16
Symbol
VP EN/SET SEL VIN N/C SW PGND
Function
Input power pin; connected to the source of the P-channel MOSFET. Connect a 2.2F or larger capacitor from these pins to PGND. IC active high enable pin. Alternative input pin for S2Cwire control utilizing FB2 reference. Logic high selects FB1 high output reference; logic low selects FB2 low output reference. Pull low for S2Cwire control. See Tables 1 and 2. Input voltage for the converter. Connect this pin directly to the VP pin. No connection. Do not make any connection to this pin. Boost converter switching node. Connect the power inductor between the SW pin and the LIN pin. Power ground for the boost converter; connected to the source of the internal N-channel MOSFET. Connect input and output capacitor returns to PGND. Ground pin. Feedback pin for low output voltage set point. Pin set to 0.6V when SEL is low and disabled when SEL is high. Voltage is set from 0.6V to 1.2V using S2Cwire control. Feedback pin for high output voltage set point. Pin set to 1.2V when SEL is high and disabled when SEL is low. Disabled with S2Cwire control. Switched power input. Connected to the power inductor. Exposed paddle (bottom). Internally connected to SW. May be externally connected to SW pins or left floating. Do not connect to GND or PGND.
1 2 3 4 5 6, 7 8
15, 16 14 13 12 11 9, 10 6, 7, 8
9 10
5 4
GND FB2
11
3
FB1
12 N/A
1, 2 EP
LIN
Pin Configuration
TSOPJW-12 (Top View) TDFN34-16 (Top View)
VP EN/SET SEL VIN N/C SW
1 2 3 4 5 6
12 11 10 9 8 7
LIN FB1 FB2 GND PGND SW
LIN LIN FB1 FB2 GND PGND PGND PGND
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
VP VP EN/SET SEL VIN N/C SW SW
2
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AAT1232
24V 100mA Step-Up Converter Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Symbol
VIN, VP SW LIN, EN/SET, SEL, FB1, FB2 TJ TS TLEAD
Description
Input Voltage Switching Node Maximum Rating Operating Temperature Range Storage Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 28 VIN + 0.3 -40 to 150 -65 to 150 300
Units
V V V C C C
Recommended Operating Conditions
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation (TA = 25C) TDFN34-16 TSOPJW-12 TDFN34-16 TSOPJW-12
Value
44 160 2270 625
Units
C/W mW
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 1232.2007.06.1.5
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AAT1232
24V 100mA Step-Up Converter Electrical Characteristics1
TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.6V. Symbol
Power Supply VIN VOUT(MAX) VUVLO
Description
Input Voltage Range Maximum Output Voltage UVLO Threshold
Conditions
Min
2.7
Typ
Max
5.5 24 2.7
Units
V V V mV V mA
IQ ISHDN IOUT FB1 FB2 VLOADREG VLINEREG/VIN RDS(ON)L RDS(ON)IN TSS TSD THYS ILIM SEL, EN/SET VSEL(L) VSEL(H) VEN/SET(L) VEN/SET(H) TEN/SET LO TEN/SET HI MIN TEN/SET HI MAX TOFF TLAT IEN/SET
Quiescent Current
VIN Pin Shutdown Current Output Current FB1 Reference Voltage FB2 Reference Voltage Load Regulation Line Regulation Low Side Switch On Resistance Input Disconnect Switch On Resistance Soft-Start Time Over-Temperature Shutdown Threshold Shutdown Hysteresis N-Channel Current Limit SEL Threshold Low SEL Threshold High Enable Threshold Low Enable Threshold High EN/SET Low Time Minimum EN/SET High Time Maximum EN/SET High Time EN/SET Off Timeout EN/SET Latch Timeout EN/SET Input Leakage
VIN Rising Hysteresis VIN Falling SEL = GND, VOUT = 18V, IOUT = 0, R3 = 20k2, Switching SEL = GND, FB2 = 1.5V, Not Switching EN/SET = GND 2.7V < VIN < 5.5V, VOUT = 24V IOUT = 0 to 100mA, VIN = 2.7V to 5.0V, SEL = High IOUT = 0 to 100mA, VIN = 2.7V to 5.0V, SEL = Low IOUT = 0 to 100mA, R3 = 20k3 VIN = 2.7V to 5.5V, R3 = 20k3
150 1.8 0.3 40 70 1.0 100 1.164 0.582 1.2 0.6 0.02 0.6 0.08 0.18 1.236 0.618
A A mA V V %/mA %/V ms C C A
From Enable to Output Regulation; VOUT = 15V
0.35 140 15 3.0 0.4 1.4 0.4 1.4 0.3 50 75 500 500 1 75
VIN = 3.6V VIN VIN VIN VIN = = = = 2.7V 5.5V 2.7V 5.5V
-1
V V V V s ns s s s A
1. The AAT1232 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Switching input current will vary with R1, R2, R3 resistor values. 3. Some improvement in line and load regulation is possible with smaller resistor values.
4
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AAT1232
24V 100mA Step-Up Converter Typical Characteristics
Efficiency vs. Output Current
(VOUT = 18V; R3 = 20k)
90 80
Output Error vs. Output Current
(VOUT = 18V; R3 = 20k)
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5
VIN = 5V VIN = 4.2V VIN = 3.6V
VIN = 5V
70 60 50 40 30 20 0.1 1
Output Error (%)
Efficiency (%)
VIN = 4.2V VIN = 3.6V VIN = 2.7V
0.1 1 10 100
10
100
Output Current (mA)
Output Current (mA)
Efficiency vs. Output Current
(VOUT = 20V; R3 = 20k)
90 80
Output Error vs. Output Current
(VOUT = 20V; R3 = 20k)
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5
VIN = 5V VIN = 4.2V VIN = 3.6V
VIN = 5V VIN = 4.2V VIN = 3.6V VIN = 2.7V
70 60 50 40 30 20 0.1 1
Output Error (%)
Efficiency (%)
10
100
0.1
1
10
100
Output Current (mA)
Output Current (mA)
Efficiency vs. Output Current
(VOUT = 24V; R3 = 20k)
90 80
Output Error vs. Output Current
(VOUT = 24V; R3 = 20k) VIN = 4.2V
1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5
VIN = 5V
VIN = 5V
70 60 50 40 30 20 0.1 1 10 100
VIN = 4.2V
VIN = 3.6V
Output Error (%)
Efficiency (%)
VIN = 3.6V VIN = 2.7V
0.1
1
10
100
Output Current (mA)
Output Current (mA)
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AAT1232
24V 100mA Step-Up Converter Typical Characteristics
(VOUT = 18V; R3 = 20k)
2.5 2.0 1.5 0.2 0.1
Line Regulation
Output Voltage Error vs. Temperature
(VIN = 5V; VOUT = 18V; IOUT = 100mA)
Output Error (%)
Accuracy (%)
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 2.5 3 3.5 4 4.5 5 5.5 6
0.0 -0.1 -0.2 -0.3 -0.4 -0.5 -40 -15 10 35 60 85
Input Voltage (V)
Temperature (C)
No Load Quiescent Current vs. Input Voltage
(VOUT = 18V; EN_High)
0.4
No Load Input Current vs. Temperature
(VIN = 3.6V; VOUT = 18V)
1.2 1.1 0.9 0.8 0.6 0.5 0.3 0.2 0.0 -40 -15 10 35 60 85
Supply Current (mA)
0.32 0.28 0.24 0.2 0.16 0.12 0.08 2.5 3 3.5 4 4.5 5 5.5
Supply Current (mA)
0.36
Input Voltage (V)
Temperature (C)
Output Ripple
(VIN = 4.2V; VOUT = 18V; IOUT = 100mA)
18.2 18.0 5.0 4.0 3.0 2.0 1.0 0.0 -1.0 18.2 18.0
Output Ripple
(VIN = 4.2V; VOUT = 18V; No Load)
1.0 0.8 0.6 0.4 0.2 0.0 -0.2
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
Output Voltage (top) (V)
17.8 17.6 17.4 17.2 17.0
Output Voltage (top) (V)
17.8 17.6 17.4 17.2 17.0
Time (500ns/div)
Time (100s/div)
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AAT1232
24V 100mA Step-Up Converter Typical Characteristics
Load Transient Response
(VIN = 4.2V; IOUT = 20mA-60mA; VOUT = 18V)
Load Transient Response
(VIN = 3.6V; IOUT = 20mA-60mA; VOUT = 12V)
Inductor Current (A) (bottom)
Inductor Current (A) (bottom)
18.10
1.5 1.2 0.9 0.6 0.3 0.0 -0.3
12.10
1.50 1.20 0.90 0.60 0.30 0.00 -0.30
Output Voltage (V) (top)
Output Voltage (V) (top)
18.05 18.00 17.95 17.90 17.85 17.80
12.05 12.00 11.95 11.90 11.85 11.80
Time (200s/div)
Time (200s/div)
P-Channel RDS(ON) vs. Input Voltage
300 280 160 140
N-Channel RDS(ON) vs. Input Voltage
RDS(ON) (m)
RDS(ON) (m)
260 240 220 200 180 160 140 2.5 3
120C
100C
120 100 80 60 40 2.5 3 3.5
120C
100C
25C
25C
85C
3.5 4 4.5 5 5.5 6
85C
4 4.5 5 5.5 6
Input Voltage (V)
Input Voltage (V)
Soft Start
(VIN = 3.6V; CIN = 2.2F; IOUT = 100mA; VOUT = 12V)
Enable Voltage (middle) (V) Output Voltage (top) (V)
16 12 8 4 0 -4 -8 -12 -16
2.8 2.4 2.0 1.6 1.2 0.8 0.4 0.0 -0.4
Input Current (bottom) (A)
Time (200s/div)
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AAT1232
24V 100mA Step-Up Converter Functional Block Diagram
VIN
VP
LIN
Output Timer EN/SET Control FB1
1.2V
SW
VREF
Output Select
FB2 SEL
GND
PGND
Functional Description
The AAT1232 consists of a DC/DC boost controller, an integrated slew rate controlled input disconnect MOSFET switch, and a MOSFET power switch. A high voltage rectifier, power inductor, output capacitor, and resistor divider network are required to implement a DC/DC boost converter.
The AAT1232 modulates the power MOSFET switching current in response to changes in output voltage. This allows the voltage loop to directly program the required inductor current in response to changes in the output load. The switching cycle initiates when the N-channel MOSFET is turned ON and current ramps up in the inductor. The ON interval is terminated when the inductor current reaches the programmed peak current level. During the OFF interval, the input current decays until the lower threshold, or zero inductor current, is reached. The lower current is equal to the peak current minus a preset hysteresis threshold - which determines the inductor ripple current. The peak current is adjusted by the controller until the output current requirement is met.
Control Loop
The AAT1232 provides the benefits of current mode control with a simple hysteretic feedback loop. The device maintains exceptional DC regulation, transient response, and cycle-by-cycle current limit without additional compensation components.
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AAT1232
24V 100mA Step-Up Converter
The magnitude of the feedback error signal determines the average input current. Therefore, the AAT1232 controller implements a programmed current source connected to the output capacitor and load resistor. There is no right-half plane zero, and loop stability is easily achieved with no additional compensation components. Increased load current results in a drop in the output feedback voltage (FB1 or FB2) sensed through the feedback resistors (R1, R2, R3). The controller responds by increasing the peak inductor current, resulting in higher average current in the inductor. Alternatively, decreased output load results in an increase in the output feedback voltage (FB1 or FB2 pin). The controller responds by decreasing the peak inductor current, resulting in lower average current in the inductor. At light load, the inductor OFF interval current goes below zero and the boost converter enters discontinuous mode operation. Further reduction in the load results in a corresponding reduction in the switching frequency. AAT1232 pulsed frequency operation reduces switching losses and maintains high efficiency at light loads. Operating frequency varies with changes in the input voltage, output voltage, and inductor size. Once the boost converter has reached continuous mode, further increases in the output load will not significantly increase the operating frequency. A small 2.2H (20%) inductor is selected to maintain high frequency switching (up to 2MHz) and high efficiency operation for outputs from 10V to 24V. Alternatively, the output voltage may be programmed to any of 16 voltage levels using the S2Cwire serial digital input. The single wire S2Cwire interface provides high-speed output voltage programmability across a 2X output voltage range. S2Cwire functionality is enabled by pulling the SEL pin low and providing S2Cwire input to the EN/SET pin. Table 2 details the FB2 reference voltage versus S2Cwire rising edges.
Soft Start / Enable
The input disconnect switch is activated when a valid input voltage is present and the EN/SET pin is pulled high. The slew rate control on the P-channel MOSFET ensures minimal inrush current as the output voltage is charged to the input voltage, prior to switching of the N-channel power MOSFET. Monotonic turn-on is guaranteed by the builtin soft-start circuitry. Soft-start eliminates output voltage overshoot across the full input voltage range and all loading conditions. Some applications may require the output to be active when a valid input voltage is present. In these cases, add a 10k resistor between the VIN, VP, and EN/SET pins to avoid startup issues.
Current Limit and Over-Temperature Protection
The switching of the N-channel MOSFET terminates when current limit of 3.0A (typical) is exceeded. This minimizes power dissipation and component stresses under overload and short-circuit conditions. Switching resumes when the current decays below the current limit. Thermal protection disables the AAT1232 when internal dissipation becomes excessive. Thermal protection disables both MOSFETs. The junction over-temperature threshold is 140C with 15C of temperature hysteresis. Once an over-temperature or over-current fault condition is removed, the output voltage automatically recovers.
Output Voltage Programming
The output voltage may be programmed through a resistor divider network located from output capacitor to FB1/FB2 pins to ground. Pulling the SEL pin high activates the FB1 pin which maintains a 1.2V reference voltage, while the FB2 reference is disabled. Pulling the SEL pin low activates the FB2 pin which maintains a 0.6V reference, while the FB1 reference is disabled. This function allows dynamic selection between two distinct output voltages across a 2X range (maximum). An additional resistor between FB1 and FB2 allows the designer to program the outputs across a reduced <2X range.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN input. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuitry prior to activation.
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AAT1232
24V 100mA Step-Up Converter
L1 2.2H
12 11 10 9 8 7
JP1
3 2 1
R4 10k
VIN
1 2 3 4 5 6
U1
D1 Schottky
VOUT
Enable JP2
3 2 1
C1 2.2F
VP LIN EN/SET FB1 SEL FB2 VIN GND N/C PGND SW SW
R1 576k R2 10k R3 20k
C2 2.2F
Select U1 AAT1232 TSOPJW12 C1 10V 0805 2.2F C2 25V 0805 2.2F D1 30V 0.5A MBR0530T SOD-123 L1 2.2H NR4018T2R2 R1 576k 0603 R2, R4 10k 0603 R3 20k 0603 R4 10k 0603
Figure 1: AAT1232 Demo Board Schematic.
Application Information
Selecting DC/DC Boost Capacitors
The high output ripple inherent in the boost converter necessitates low impedance output filtering. Multi-layer ceramic (MLC) capacitors provide small size and adequate capacitance, low parasitic equivalent series resistance (ESR) and equivalent series inductance (ESL), and are well suited for use with the AAT1232 boost regulator. MLC capacitors of type X7R or X5R are recommended to ensure good capacitance stability over the full operating temperature range. The output capacitor is sized to maintain the output load without significant voltage droop during the power switch ON interval, when the output diode is not conducting. A ceramic output capacitor from 2.2F to 4.7F is recommended. Typically, 25V rated ceramic capacitors are required for the 24V boost output. Ceramic capacitors sized as small as 0805 are available which meet these requirements. MLC capacitors exhibit significant capacitance reduction with applied voltage. Output ripple measurements should confirm that output voltage droop is acceptable. The boost converter input current flows during both ON and OFF switching intervals. The input ripple current is less than the output ripple and, as a result, less input capacitance is required. A ceramic output capacitor from 1F to 3.3F is recommended. 10
Minimum 6.3V rated ceramic capacitors are required at the input. Ceramic capacitors sized as small as 0603 are available which meet these requirements. Large capacitance tantalum or solid-electrolytic capacitors may be necessary to meet stringent output ripple and transient load requirements. These can replace (or be used in parallel with) ceramic capacitors. Both tantalum and OSCON-type capacitors are suitable due to their low ESR and excellent temperature stability (although they exhibit much higher ESR than MLC capacitors). Aluminum-electrolytic types are less suitable due to their high ESR characteristics and temperature drift. Unlike MLC capacitors, these types are polarized and proper orientation on input and output pins is required. 30% to 70% voltage derating is recommended for tantalum capacitors.
Selecting the Output Diode
To ensure minimum forward voltage drop and no recovery, high voltage Schottky diodes are considered the best choice for the AAT1232 boost converter. The AAT1232 output diode is sized to maintain acceptable efficiency and reasonable operating junction temperature under full load operating conditions. Forward voltage (VF) and package thermal resistance (JA) are the dominant factors to consider in selecting a diode. The diode's published current rating may not reflect actual operating conditions and should be used only as a comparative measure between similarly rated devices. 20V rated Schottky
1232.2007.06.1.5
AAT1232
24V 100mA Step-Up Converter
diodes are recommended for outputs less than 15V, while 30V rated Schottky diodes are recommended for outputs greater than 15V. The average diode current is equal to the output current.
IAVG = IOUT
1 = TON + TOFF FS
The ON time is the period which the N-channel power MOSFET is conducting and storing energy in the boost inductor. Duty cycle is defined as the ON time divided by the total switching interval.
The average output current multiplied by the forward diode voltage determines the loss of the output diode.
PLOSS_DIODE = IAVG * VF = IOUT * VF
D=
TON TON + TOFF
= TON FS
The maximum duty cycle can be estimated from the relationship for a continuous mode boost converter. Maximum duty cycle (DMAX) is the duty cycle at minimum input voltage (VIN(MIN)).
Diode junction temperature can be estimated.
TJ = TAMB + JA * PLOSS_DIODE
DMAX =
(VOUT + VF - VIN(MIN)) (VOUT + VF)
The junction temperature should be maintained below 110C, but may vary depending on application and/or system guidelines. The diode JA can be minimized with additional PCB area on the cathode. PCB heatsinking the anode may degrade EMI performance. The reverse leakage current of the rectifier must be considered to maintain low quiescent (input) current and high efficiency under light load. The rectifier reverse current increases dramatically at high temperatures.
Where VF is the Schottky diode forward voltage and can be estimated at 0.5V. Manufacturer's specifications list both the inductor DC current rating, which is a thermal limitation, and peak inductor current rating, which is determined by the saturation characteristics. Measurements at full load and high ambient temperature should be completed to ensure that the inductor does not saturate or exhibit excessive temperature rise. The output inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions. Peak current may be calculated from the following equation, again assuming continuous conduction mode. Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load. Switching frequency can be estimated at 500kHz with a 2.2H inductor.
Selecting the Boost Inductor
The AAT1232 controller utilizes hysteretic control and the switching frequency varies with output load and input voltage. The value of the inductor determines the maximum switching frequency of the AAT1232 boost converter. Increased output inductance decreases the switching frequency, resulting in higher peak currents and increased output voltage ripple. To maintain 2MHz maximum switching frequency, an output inductor sized from 1.5H to 2.7H is recommended. The switching period is divided between ON and OFF time intervals.
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IPEAK =
IOUT D * VIN(MIN) + MAX (1 - DMAX) (2 * FS * L)
The RMS current flowing through the boost inductor is equal to the DC plus AC ripple components. Under worst-case RMS conditions, the current waveform is critically continuous. The resulting 11
AAT1232
24V 100mA Step-Up Converter
RMS calculation yields worst-case inductor loss. The RMS value should be compared against the manufacturer's temperature rise, or thermal derating, guidelines. or low. Second, the output voltage can be dynamically adjusted between two pre-set levels within a 2X operating range by toggling the SEL logic pin. Third, the output can be dynamically adjusted to any of 16 preset levels within a 2X operating range using the integrated S2Cwire single wire interface via the EN/SET pin. Option 1: Static Output Voltage A static output voltage can be configured by pulling the SEL either high or low. SEL pin high activates the FB1 reference pin to 1.2V (nominal). Alternatively, the SEL pin is pulled low to activate the FB2 reference at 0.6V (nominal). Table 1 provides details of resistor values for common output voltages from 10V to 24V for SEL = High and SEL = Low options. In the static configuration, the FB1 pin should be directly connected to FB2. The resistor between FB1 and FB2 pins is not required. Option 2: Dynamic Voltage Control Using SEL Pin The output may be dynamically adjusted between two output voltages by toggling the SEL logic pin. Output voltages VOUT(1) and VOUT(2) correspond to the two output references, FB1 and FB2. Pulling the SEL logic pin high activates VOUT(1), while pulling the SEL logic pin low activates VOUT(2). The minimum output voltage must be greater than the specified maximum input voltage plus margin to maintain proper operation of the AAT1232 boost converter. In addition, the ratio of output voltages VOUT(2)/VOUT(1) is always less than 2.0, corresponding to a 2X (maximum) programmable range. Table 1 is provided to allow programming of common output voltages using Option 1 or 2. The feedback references FB1 and FB2 are enabled or disabled using the SEL logic pin, corresponding to VOUT(1) and VOUT(2). Option 3: Dynamic Voltage Control Using S2Cwire Interface The output can be dynamically adjusted by the host controller to any of 16 pre-set output voltage levels using the integrated S2Cwire interface. The EN/SET pin serves as the S2Cwire interface input. The SEL pin must be pulled low when using the S2Cwire interface.
IRMS =
IPEAK
3
For a given inductor type, smaller inductor size leads to an increase in DCR winding resistance and, in most cases, increased thermal impedance. Winding resistance degrades boost converter efficiency and increases the inductor operating temperature.
PLOSS_INDUCTOR = IRMS2 * DCR
To ensure high reliability, the inductor temperature should not exceed 100C. Manufacturer's recommendations should be consulted. In some cases, PCB heatsinking applied to the AAT1232 LIN node (non-switching) can improve the inductor's thermal capability. PCB heatsinking may degrade EMI performance when applied to the SW node (switching) of the AAT1232. Shielded inductors provide decreased EMI and may be required in noise sensitive applications. Unshielded chip inductors provide significant space savings at a reduced cost compared to shielded (wound and gapped) inductors. Chip-type inductors have increased winding resistance when compared to shielded, wound varieties.
Setting the Output Voltage
The output voltage may be programmed through a resistor divider network located from the output to FB1 and FB2 pins to ground. Pulling the SEL pin high activates the FB1 pin which maintains a 1.2V reference voltage, while the FB2 reference is disabled. Pulling the SEL pin low activates the FB2 pin which maintains a 0.6V reference, while the FB1 reference is disabled. The AAT1232 output voltage can be programmed by one of three methods. First, the output voltage can be static by pulling the SEL logic pin either high
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AAT1232
24V 100mA Step-Up Converter
VOUT (SEL = High)
10.0 12.0 15.0 16.0 18.0 20.0 24.0 12.0 15.0 16.0 18.0 15.0 16.0 18.0 18.0 20.0 24.0 24.0
VOUT (SEL = Low)
10.0 12.0 15.0 16.0 18.0 20.0 24.0 10.0 10.0 10.0 10.0 12.0 12.0 12.0 15.0 15.0 15.0 18.0
R3 = 4.99k
R3 = 20.0k
R1 (k)
36.5 44.2 57.6 61.9 69.8 78.7 95.3 78.7 95.3 121 127 143 162 196 75.0 76.8 76.8 78.7 90.9 93.1 93.1 115 118 118 143
R2 (k)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 3.32 1.65 1.24 0.562 3.01 2.49 1.65 3.32 2.49 1.24 2.49
R1 (k)
147 182 232 249 280 316 383 316 383 487 511 590 649 787 301 309 309 316 374 374 374 464 475 475 576
R2 (k)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 13.0 6.65 4.99 2.21 12.1 10.0 6.65 13.3 10.0 4.99 10.0
Table 1: SEL Pin Voltage Control Resistor Values (1% resistor tolerance).
S2Cwire Serial Interface
AnalogicTech's S Cwire serial interface is a proprietary high-speed single-wire interface available only from AnalogicTech. The S2Cwire interface records rising edges of the EN/SET input and decodes into 16 different states. Each state corresponds to a voltage setting on the FB2 pin.
2
register is reset to the default value, which sets the FB2 pin to 0.6V if EN is subsequently pulled high. EN/SET Rising Edges
1 2 3 4 5 6 7 8
FB2 Reference Voltage (V)
0.60 (Default) 0.64 0.68 0.72 0.76 0.80 0.84 0.88
EN/SET Rising Edges
9 10 11 12 13 14 15 16
FB2 Reference Voltage (V)
0.92 0.96 1.00 1.04 1.08 1.12 1.16 1.20
S2Cwire Serial Interface Timing
The S2Cwire serial interface has flexible timing. Data can be clocked-in at speeds up to 1MHz. After data has been submitted, EN/SET is held high to latch the data for a period TLAT. The output is subsequently changed to the predetermined voltage. When EN/SET is set low for a time greater than TOFF, the AAT1232 is disabled. When disabled, the
Table 2: S2Cwire Voltage Control Settings (SEL = Low).
1232.2007.06.1.5
13
AAT1232
24V 100mA Step-Up Converter
THI TLO T LAT TOFF
EN/SET
1 2 n-1 n 16
Data Reg
0
n-1
0
Figure 3: S2Cwire Timing Diagram to Program the Output Voltage.
S2Cwire Output Voltage Programming
The AAT1232 is programmed through the S2Cwire interface according to Table 2. The rising clock edges received through the EN/SET pin determine the feedback reference and output voltage setpoint. Upon power up with the SEL pin low and prior to S2Cwire programming, the default feedback reference voltage is set to 0.6V.
PCB Layout Guidelines
Boost converter performance can be adversely affected by poor layout. Possible impact includes high input and output voltage ripple, poor EMI performance, and reduced operating efficiency. Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray resistance, capacitance, inductance) and EMI coupling from the high frequency SW node. A suggested PCB layout for the AAT1232 boost converter is shown in Figures 4 and 5. The following PCB layout guidelines should be considered:
1. Minimize the distance from capacitor C1 and C2 negative terminal to the PGND pins. This is especially true with output capacitor C2, which conducts high ripple current from the output diode back to the PGND pins. 2. Place the feedback resistors close to the output terminals. Route the output pin directly to resistor R1 to maintain good output regulation. R3 should be routed close to the output GND pin. 3. Minimize the distance between L1 to D1 and switching pin SW; minimize the size of the PCB area connected to the SW pin. 4. Maintain a ground plane and connect to the IC RTN pin(s) as well as the GND terminals of C1 and C2. 5. Consider additional PCB area on D1 cathode to maximize heatsinking capability. This may be necessary when using a diode with a high thermal resistance. 6. When using the TDFN34-16 package, connect paddle to SW pin or leave floating. Do not connect to RTN/GND conductors. 7. To avoid problems at startup, add a 10k resistor between the VIN, VP and EN/SET pins (R4). This is critical in applications requiring immunity from input noise during "hot plug" events, e.g. when plugged into an active USB port.
14
1232.2007.06.1.5
AAT1232
24V 100mA Step-Up Converter
Figure 4: AAT1232 Evaluation Board Top Side.
Figure 5: AAT1232 Evaluation Board Bottom Side.
1232.2007.06.1.5
15
AAT1232
24V 100mA Step-Up Converter
Manufacturer
Diodes, Inc. Diodes, Inc. Diodes, Inc. Diodes, Inc. ON Semi ON Semi Zetex Zetex
Part Number
B340LA SD103AWS BAT42WS B0520WS MBR130LSFT MBR0530T ZHCS350 BAT54
Rated IF(AV) Current (A)1
3.00 0.35 0.20 0.50 1.00 0.50 0.35 0.20
Rated Voltage (V)
40 30 30 20 30 30 40 30
Thermal Resistance (JA, C/W)1
25 625 625 426 325 206 330 330
Case
SMA SOD-323 SOD-323 SOD-323 SOD-123 SOD-123 SOD-523 SOT-23
Table 3: Typical Surface Mount Schottky Rectifiers for Various Output Loads. (select TJ < 110C in application circuit). Inductance (H)
2.2 2.4 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2
Manufacturer
Sumida Sumida Sumida Murata Murata Taiyo Yuden Taiyo Yuden Coiltronics Coiltronics Coiltronics
Part Number
CDRH4D22/HP-2R2 CDR4D11/HP-2R4 CDRH4D18-2R2 LQH662N2R2M03 LQH55DN2R2M03 NR4018T2R2 NR3015T2R2 SD3814-2R2 SD3114-2R2 SD3112-2R2
Max DC ISAT Current (A)
2.50 1.70 1.32 3.30 3.20 2.70 1.48 1.90 1.48 1.12
DCR ()
35 105 75 19 29 60 60 77 86 140
Size (mm) LxWxH
5.0x5.0x2.4 4.8x4.8x1.2 5.0x5.0x2.0 6.3x6.3x4.7 5.0x5.7x4.7 4.0x4.0x1.8 3.0x3.0x1.5 3.8x3.8x1.4 3.1x3.1x1.4 3.1x3.1x1.2
Type
Shielded Shielded Shielded Shielded Non-Shielded Shielded Shielded Shielded Shielded Shielded
Table 4: Typical Surface Mount Inductors for Various Output Loads (select IPEAK < ISAT).
Manufacturer
Murata Murata Murata Murata Murata
Part Number
GRM188R60J475KE19D GRM188R61A225KE34D GRM188R61C225KA88 GRM21BR61E225KA12L GRM188R61E105KA12D
Type
Ceramic Ceramic Ceramic Ceramic Ceramic
Value (F)
2.2 2.2 2.2 2.2 1.0
Voltage (V)
6.3 10 16 25 25
Temp. Co.
X5R X5R X5R X5R X5R
Footprint LxWxH (mm)
0603 0603 0805 0805 0603
Table 5: Typical Surface Mount Capacitors for Various Output Loads.
1. Results may vary depending on test method used and specific manufacturer.
16
1232.2007.06.1.5
AAT1232
24V 100mA Step-Up Converter Ordering Information
Package
TSOPJW-12 TDFN34-16
Marking1
SXXYY SXXYY
Part Number (Tape and Reel)2
AAT1232ITP-T1 AAT1232IRN-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Package Information3
TSOPJW-12
0.10 0.20 + 0.05 -
2.40 0.10
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
2.85 0.20
7 NOM 3.00 0.10
0.9625 0.0375 + 0.10 1.00 - 0.065
0.04 REF
0.15 0.05
0.055 0.045
4 4
0.010
0.45 0.15 2.75 0.25
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 1232.2007.06.1.5
17
AAT1232
24V 100mA Step-Up Converter
TDFN34-16
3.000 0.050
1.600 0.050 Detail "A"
Index Area
4.000 0.050
3.300 0.050
0.350 0.100
Top View
Bottom View
C0.3
0.230 0.050
(4x)
0.850 MAX
0.050 0.050
0.229 0.051
Side View Detail "A"
All dimensions in millimeters.
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18
1232.2007.06.1.5
0.450 0.050
Pin 1 Indicator (optional)

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