Document
Features
z 2A Output Current Wide 4.5V to 28V Operating Input Range
z Integrated Power MOSFET switches z Output Adjustable from 0.925V to 0.8Vin z Up to 96% Efficiency z Programmable Soft-Start z Stable with Low ESR Ceramic Output
Capacitors z Fixed 340KHZ Frequency z Cycle-by-Cycle Over Current Protection z Short Circuit Protection z Input Under Voltage Lockout
z Package: SOP-8L
HT3420
2A 28V Synchronous Buck Converter
General Description
The HT3420 is a monolithic synchronous buck regulator. The device integrates 95 mΩ MOSFETS that provide 2A continuous load current over a wide operating input voltage of 4.5V to 28V. Current mode control provides fast transient response and cycleby-cycle current limit. An adjustable softstart prevents inrush current at turn on.
Applications
z Distributed Power Systems z Networking Systems z FPGA, DSP, ASIC Power Supplies
z Green Electronics/ Appliances z Notebook Computers
Typical Application Circuit
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Ordering Information
HT3420
Pin Assignments
Pin Descriptions
Pin Number 1
2 3 4
5
6
Name BS
VIN SW GND
FB
COMP
7 EN
8 SS
BS 1 VIN 2 SW 3 GND 4
SOP-8L (TOP View)
8 SS 7 EN 6 COMP 5 FB
Description
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 0.01uF capacitor between BS and SW.
Input Supply. Bypass this pin to GND with a low ESR capacitor. See Input Capacitor in the Application Information section.
Switch Output. Connect this pin to the switching end of the inductor.
Ground.
Feedback Input. The voltage at this pin is regulated to 0.925V. Connect to the resistor divider between output and ground to set output voltage.
Compensation Pin. See Stability Compensation in the Application Information section.
Enable Input. When higher than 2.7V, this pin turns the IC on. When lower than 1.1V, this pin turns the IC off. Output voltage is discharged when the IC is off. This pin should not be left open. Recommend to put a 100KΩ pull up resistor to Vin for start up.
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1uF capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected.
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HT3420
Block Diagram
FB 5
1.1V
0.3V
OVP
RAMP
OSCILLATOR 340/120KHz CLK
SS 8 0.925V
COMP 6 EN 7
2.5V
ERROR AMPLIFIER
6uA
EN OK LOCKOUT COMPARATOR
1.5V
SHUTDOWN COMPARATOR
CURRENT SENSE
AMPLIFIER
SQ RQ CURRENT COMPARATOR
2 VIN 5V
1 BS
3 SW
1.2V
OVP
4 GND
IN<4.10V
IN
INTERNAL REGULATORS
Absolute Maximum Ratings
Parameter
Value
Unit
Input Supply Voltage
-0.3 to 30
V
SW Voltage BS Voltage EN, FB, COMP Voltage
-0.3 to VIN + 0.3 VSW – 0.3 to VSW + 6
-0.3 to 5.
V V V
Continuous SW Current
Internally limited
A
Junction (Test on
to Ambient Thermal Approximately 3 in2
Resistance (θJA) Copper Area 1oz
copper
FR4
board)
87
°C/W
SOP-8L Power Dissipation
Internal limit
W
Maximum Junction Temperature
150 °C
Storage Temperature Range
-65 to 150
°C
Moisture Sensitivity (MSL)
Please refer the MSL label on the IC package
bag/carton for detail
(Note: Exceeding these limits may damage the device., Even the duration of exceeding is very short. Exposure to absolute maximum rating conditions for long periods may affect device reliability.)
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HT3420
Recommended Operating Conditions
Parameter
Min
Input Supply Voltage
4.5
Operating Junction Temperature
-20
Max 28 (1) +125 (2)
Unit V °C
(Note (1): Operating the IC over this voltage is very easy to cause over voltage condition to VIN pin, SW pin, BS pin & EN pin)
(Note (2): If the IC experienced OTP, then the temperature may need to drop to <125 degree C to let the IC recover.)
Electrical Characteristics
(VIN = 12V, TA= 25°C unless otherwise specified.)
Parameter Feedback Voltage Feedback Overvoltage Threshold
Symbol VFB
High-Side Switch-On Resistance*
Low-Side Switch-On Resistance*
High-Side Switch Leakage
Upper Switch Current Limit*
COMP to Current Limit Transconductance
GCOMP
Error Amplifier Transconductance Error Amplifier DC Gain* Switching Frequency Short Circuit Switching Frequency
GEA AVEA fSW
Maximum Duty Cycle Minimum On Time*
DMAX
EN Shutdown Threshold Voltage
EN Shutdown Threshold Voltage
Hysteresis
EN Lockout Threshold Voltage
EN Lockout Hysteresis
Supply Current in Shutdown
IC Supply Current in Operation
Input UVLO Threshold Rising
UVLO
Input UVLO Threshold Hysteresis
Soft-start Current
Soft-start Period
Thermal Shutdown Temperature*
Note: * Guaranteed by design, not tested
Test Conditions 4.5V ≤ VIN 28V
VEN = 0V, VSW = 0V Minimum Duty Cycle
ΔICOMP = ±10uA
VFB = 0 VFB = 0.8V VEN Rising
VEN = 0 VEN = 3V, VFB = 1.0V
VEN Rising VSS = 0V CSS = 0.1uF Hysteresis = 25°C
Min 0.900
2.7
Typ 0.925
1.1 95 95
3.5
Max 0.950
10
Unit V V mΩ mΩ uA A
3.3 A/V
920 480 340 120 92 220 1.1 1.4
uA/V V/V KHz KHz % nS 2V
180 mV
2.2 3.80
2.5 130 0.3 1.3 4.05 100
6 15 160
2.7
3.0 1.5 4.40
V mV uA .