1 Introduction
User's Guide
SNVA353B–February 2009–Revised April 2013
AN-1870 LM26420 Evaluation Board
The LM26420 evaluation board was designed to provide two 2A outputs, V
either the HTSSOP package option of the LM26420 for easier probing or the WQFN version for evaluating
the smaller package. The design emphasizes on the compactness of the LM26420 PCB layout and is
thermally optimized. The total solution size is less than 35mm by 40mm. The board supports the
conversion from an input voltage ranging from 3V to 5.5V down to output voltages of 0.8V for each
channel. V
OUT1
and V
are set to 1.2V and 2.5V respectively. The feedback resistor can be changed to
OUT2
support output voltages as low as 0.8V or as high at 4.5V, assuming VINis high enough to support it. The
EN pins are pulled up to VINby jumpers for easy evaluation but can also be easily controlled by external
logic.
The board’s specifications are:
• Input Voltage: 3V to 5.5V
• Output Voltages: 1.2V
OUT1
• Maximum load current: 2A/output
• Minimum load current: 0A
• Size: 1.35 in. × 1.6 in.
• Peak Current Limit: ≊ 3.2A at 25°C
• Nominal Switching Frequency: 550 kHz or 2.2MHz
2 Powering Up the Board
Since the EN pins are directly tied to the input voltage via jumpers J1and J2, starting up the board is as
simple as connecting a voltage supply from 3V to 5.5V between the VINand GND terminals. There should
be 1.2V on V
care should be taken in powering up the supplies such that the input voltage, VIN, does not exceed the
Absolute Maximum Rating of 7V. If the part experiences voltages greater than 7V for a prolonged period
of time, then damage to the part can occur and then the evaluation board may cease working.
The linear soft-start ramps for the two output voltages and should last about 600 µs. Load can be applied
prior to power-up. If an output is shorted either before or after start-up, removal of the short-circuit
condition should bring the corresponding output back to normal voltage.
and 2.5V on V
OUT1
and V
OUT1
and 2.5V
OUT2
OUT2
, assuming the jumpers connect VINto EN for each channel. Great
OUT2
. It is available in
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Typical Application Circuit
3 Typical Application Circuit
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Figure 1. LM26420 Demo Board Schematic
2
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4 16-Pin WQFN Pin Out
Pin Name Function
1,2 VIND
11, 12 VIND
15 VINC Power Input supply for control circuitry.
4 PGND
9 PGND
14 AGND Signal ground pin. Place the bottom resistor of the feedback network as close as possible to pin.
6 PG
7 PG
5 FB
8 FB
3 SW
10 SW
16 EN
13 EN
DAP Die Attach Pad Connect to system ground for low thermal impedance and as a primary electrical GND
1
2
1
2
1
2
1
2
1
2
1
2
16-Pin WQFN Pin Out
Figure 2. 16-Pin WQFN (top view)
Table 1. Pin Descriptions 16-Pin WQFN
Power Input supply for Buck1.
Power Input supply for Buck2.
Power ground pin for Buck 1.
Power ground pin for Buck 2.
Power Good Indicator for Buck 1. Pin is connected through a resistor to an external supply (open
collector output).
Power Good Indicator for Buck 2. Pin is connected through a resistor to an external supply (open
collector output).
Feedback pin for Buck 1. Connect to external resistor divider to set output voltage.
Feedback pin for Buck 2. Connect to external resistor divider to set output voltage.
Output switch for Buck 1. Connect to the inductor.
Output switch for Buck 2. Connect to the inductor.
Enable control input. Logic high enable operation for Buck 1. Do not allow this pin to float or be
greater than VIN + 0.3V.
Enable control input. Logic high enable operation for Buck 2. Do not allow this pin to float or be
greater than VIN + 0.3V.
connection.
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20-Pin HTSSOP Pin Out
5 20-Pin HTSSOP Pin Out
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Figure 3. 20-Pin HTSSOP (top view)
Table 2. Pin Descriptions 20-Pin HTSSOP
Pin Name Function
3, 4 VIND
17, 18 VIND
1 VINC Power Input supply for control circuitry.
6,7 PGND
14, 15 PGND
20 AGND Signal ground pin. Place the bottom resistor of the feedback network as close as possible to pin.
9 PG
12 PG
8 FB
13 FB
5 SW
16 SW
2 EN
19 EN
10,11 NC No Connect.
DAP Die Attach Pad Connect to system ground for low thermal impedance, but it cannot be used as a primary GND
Power Input supply for Buck1.
1
Power Input supply for Buck2.
2
Power ground pin for Buck 1.
1
Power ground pin for Buck 2.
2
Power Good Indicator for Buck 1. Pin is connected through a resistor to an external supply (open
1
drain output).
Power Good Indicator for Buck 2. Pin is connected through a resistor to an external supply (open
2
drain output).
Feedback pin for Buck 1. Connect to external resistor divider to set output voltage.
1
Feedback pin for Buck 2. Connect to external resistor divider to set output voltage.
2
Output switch for Buck 1. Connect to the inductor.
1
Output switch for Buck 2. Connect to the inductor.
2
Enable control input. Logic high enable operation for Buck 1. Do not allow this pin to float or be
1
greater than VIN + 0.3V.
Enable control input. Logic high enable operation for Buck 2. Do not allow this pin to float or be
2
greater than VIN + 0.3V.
connection.
4
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6 Schematic - X Version
Schematic - X Version
Figure 4. Schematic - X Version
Table 3. Bill of Materials - X Version
Item Designator Description Manufacturer Part No. Qty.
1 22µF, 6.3V, X5R, 1206 TDK C3216X5R0J226(M or K) 6
2 C5 0.47µF, 16V, X7R, 0603 TDK C2012X7R1C474K 1
3 L1, L2 1µH, 6.4A TDK 2
4 R1 5.1k, 1%, 603 Vishay CRCW06035K10F 1
5 R2 21.3k, 1%, 603 Vishay CRCW060321K3F 1
6 R7, R8 49.9k, 1%, 603 Vishay CRCW060349K9F 2
7 10k, 1%, 603 Vishay CRCW060310K0F 4
8 R9 5.1 Ohm, 1%, 805 Vishay CRCW06035R10F 1
9 J1, J2 Jumper for Enables Sullins Connector Solutions STC02SYAN 2
10 TP1-TP8 Keystone Electronics 5011 8
11 U1 Switcher, HTSSOP-20 or Texas Instruments LM26420 or LM26420 1
C1, C2, C3,
C4, C6, C7
SPM6530T-1R0M120 or
RLF7030T-1R0N6R4
R3, R4, R5,
R6
0.094" Diameter Solder
Terminal
Dual 2A, 2.2MHz PWM
WQFN-16
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Schematic - Y Version
7 Schematic - Y Version
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Figure 5. Schematic - Y Version
Table 4. Bill of Materials - Y Version
Item Designator Description Manufacturer Part No. Qty.
1 22µF, 6.3V, X5R, 1206 TDK C3216X5R0J226(M or K) 6
2 C5 0.47µF, 16V, X7R, 0603 TDK TMK105BJ104KV-F 1
3 L1, L2 3.3µH, 6.4A TDK or Coilcraft 2
4 R1 5.1k, 1%, 603 Vishay CRCW06035K10F 1
5 R2 21.3k, 1%, 603 Vishay CRCW060321K3F 1
6 R7, R8 49.9k, 1%, 603 Vishay CRCW060349K9F 2
7 10k, 1%, 603 Vishay CRCW060310K0F 4
8 R9 5.1 Ohm, 1%, 805 Vishay CRCW06035R10F 1
9 J1, J2 Jumper for Enables Sullins Connector Solutions STC02SYAN 2
10 TP1-TP8 Keystone Electronics 5011 8
11 U1 Switcher, HTSSOP-20 or Texas Instruments 1
C1, C2, C3,
C4, C6, C7
R3, R4, R5,
R6
0.094" Diameter Solder
Terminal
Dual 2A, 550kHz PWM
WQFN-16
RLF7030T-3R3M4R1 or
MSS7341-332NL_
LM26420YMH or
LM26420YSQ
6
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8 HTSSOP-20 PCB Layout
HTSSOP - Top Layer HTSSOP - Layer 2
HTSSOP-20 PCB Layout
HTSSOP - Layer 3 HTSSOP - Bottom Layer
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WQFN-16 PCB Layout
9 WQFN-16 PCB Layout
WQFN - Top Layer WQFN - Layer 2
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WQFN - Layer 3 WQFN - Bottom Layer
8
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10 Typical Performance Characteristics
Typical Performance Characteristics
Efficiency - 1.2V
Efficiency - 1.2V
- X Version Efficiency - 2.5V
OUT
- Y Version Efficiency - 2.5V
OUT
- X Version
OUT
- Y Version
OUT
Load Step Response - X Version Load Step Response - Y Version
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Typical Performance Characteristics
Steady State Operation - Y Version Enable
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Start-up - VINApplied
10
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