SC5832低压差低静态功耗5V降压芯片
High Efficiency 1MHz 2A Synchronous Step Down Regulator
Pin Assignments
S5 Package (SOT-23-5)
Fig ure 1. Pin Assignment of SC5832A Ordering Information
Description
The SC5832A is a high efficiency, high frequency synchronous DC-DC step-down converter. The 100% duty cycle feature provides low dropout operation, extending battery life in portable systems. The internal synchronous switch increases efficiency and eliminates the need for external Schottky diode. At shutdown mode, the input supply current is less than 1μA.
The current limit protection and on-chip thermal shutdown features provide protection against any combination of overload or ambient temperature. Features
●Low R DS(ON) for Internal Switch (Top/Bottom):
180/100m?
● 2.5V~6.5V Input Voltage Range
●2A Output Current
●1MHz Switching Frequency Minimizes the
External Components
●Internal Soft-Start Limits the Inrush Current ●Internal Compensation Function
●100% Dropout Operation
●RoHS Compliant and Halogen Free
●
SOT-23-5
Applications
●Set Top Box
●LCD TV
●Tablet
●Portable Equipment
SC5832A□□□
C: Green
TR: Tape/Reel
Package Type
S5: SOT-23-5
Typical Application Circuit
Figure 2. Schematic Diagram
Table 1. Recommended Component Values SC5832
NC
Functional Pin Description
Block Diagram
FB
GND
LX
Figure 3. Block Diagram of SC5832A
Absolute Maximum Ratings(Note 1)
● VIN to GND --------------------------------------------------------------------------------------------------- -0.3V to +6.5V
● LX to GND --------------------------------------------------------------------------------------------------- -0.3V to (V IN+0.3) ● EN, FB, PG to GND ---------------------------------------------------------------------------------------- -0.3V to V IN
●Package hermal esistance, (θJA)
SOT-23-5 ------------------------------------------------------------------------------------------ +250oC/W
●Package hermal esistance, (θJC)
SOT-23-5 ------------------------------------------------------------------------------------------ +130°C/W
● Maximum Junction Temperature (T J) ------------------------------------------------------------------- +150°C
● Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------- +260°C
● Storage Temperature (T STG) ------------------------------------------------------------------------------ -65°C to +150℃Note 1：Stresses beyond those listed under “Absolute Maximum atings" may cause permanent damage to the device
Recommended Operating Conditions(Note 2)
● Supply Voltage (V IN) ---------------------------------------------------------------------------------------- +2.5V to +5.5V ● Junction Temperature Range ---------------------------------------------------------------------------- -40°C to +125°C ● Ambient Temperature Range ----------------------------------------------------------------------------- -40°C to +85°C Note 2：The device is not guaranteed to function outside its operating conditions.
Electrical Characteristics
Typical Performance Curves
Figure 4. Efficiency vs. Load Current Figure 5. Efficiency vs. Load Current
Function Description
The SC5832A is a high efficiency, internal compensation and constant frequency current mode step-down synchronous DC/DC converter. It has integrated high-side (180mΩ, typ) and low-side (100mΩ, typ) power switches, and provides 2A continuous load current. It regulates input voltage from 2.5V to 5.5V, and down to an output voltage as low as 0.6V.
Control Loop
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load, line response, protection of the internal main switch and synchronous rectifier. The SC5832A switches at a constant frequency (1MHz) and regulates the output voltage. During each cycle, the PWM comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. During normal operation, the main switch is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until next cycle starts.
Enable
The SC5832A EN pin provides digital control to turn on/off the regulator. When the voltage of EN exceeds the threshold voltage, the regulator will start the soft start function. If the EN pin voltage is below the shutdown threshold voltage, the regulator will turn into the shutdown mode and the shutdown current will be smaller than μA. For auto start-up operation, connect EN to VIN.
Soft Start
The SC5832A employs internal soft start function to reduce input inrush current during start up. The internal soft start time will be 1ms.
Under Voltage Lockout
When the SC5832A is power on, the internal circuits will be held inactive until V IN voltage exceeds the UVLO threshold voltage. And the regulator will be disabled when V IN is below the UVLO threshold voltage. The hysteretic of the UVLO comparator is 200mV (typ). Short Circuit Protection
The SC5832A provides short circuit protection function to prevent the device damaged from short condition. When the short condition occurs and the feedback voltage drops lower than 40% of the regulation level, this will activate the latch protection circuit. Then output will be forced shutdown to prevent the inductor current runaway and to reduce the power dissipation within the IC under true short circuit conditions. Once the short condition is removed, reset EN or VIN to restart IC.
Over Current Protection
The SC5832A over current protection function is implemented by using cycle-by-cycle current limit architecture. The inductor current is monitored by measuring the high-side MOSFET series sense resistor voltage. When the load current increases, the inductor current will also increase. When the peak inductor current reaches the current limit threshold, the output voltage will start to drop. When the over current condition is removed, the output voltage will return to the regulated value. Over Temperature Protection
The SC5832A incorporates an over temperature protection circuit to protect itself from overheating. When the junction temperature exceeds the thermal shutdown threshold temperature, the regulator will be shutdown. And the hysteretic of the over temperature protection is 30°C (typ).
Application Information
Output Voltage Setting
The output voltage V OUT is set by using a resistive divider from the output to FB. The FB pin regulated voltage is 0.6V. Thus the output voltage is:
Table 2 lists recommended values of R1 and R2 for most used output voltage.
Place resistors R1 and R2 close to FB pin to prevent stray pickup.
Input Capacitor Selection
The use of the input capacitor is filtering the input voltage ripple and the MOSFETS switching spike voltage. Because the input current to the step-down converter is discontinuous, the input capacitor is required to supply the current to the converter to keep the DC input voltage. The capacitor voltage rating should be 1.25 to 1.5 times greater than the maximum input voltage. The input capacitor ripple current RMS value is calculated as:
( MS)
Where D is the duty cycle of the power MOSFET . This function reaches the maximum value at D=0.5 and the equivalent RMS current is equal to I OUT /2. The following diagram is the graphical representation of above equation.
A low ESR capacitor is required to keep the noise minimum. Ceramic capacitors are better, but
tantalum or low ESR electrolytic capacitors may also suffice.
Output Capacitor Selection
The output capacitor is used to keep the DC output voltage and supply the load transient
current. When operating in constant current mode, the output ripple is determined by four components: PPL t PPL C t PPL S t
PPL ( SL) t S t
The following figures show the form of the ripple contributions. V RIPPLE(ESR)(t)
+
V RIPPLE(ESL) (t)
+
V RIPPLE(C) (t)
+
V NOISE (t)
=
V RIPPLE (t)
0.2
0.4 0.6 0.8 1 1.2 10 20 30 40 50 60 70 80 90
I I N (R M S ) (A )
D (%)
(t)
(t)
(t)
(t)
0.5A
1A 2A
Application Information (Continued)
PPL ( S ) F SC
S PPL ( SL) SL
L SL
PPL (C)
F SC L C
Where F OSC is the switching frequency, L is the inductance value, V IN is the input voltage, ESR is the equivalent series resistance value of the output capacitor, ESL is the equivalent series inductance value of the output capacitor and the C OUT is the output capacitor.
Low ESR capacitors are preferred to use. Ceramic, tantalum or low ESR electrolytic capacitors can be used depending on the output ripple requirements. When using the ceramic capacitors, the ESL component is usually negligible.
It is important to use the proper method to eliminate high frequency noise when measuring the output ripple. The figure shows how to locate the probe across the capacitor when measuring output ripple. Remove the scope probe plastic jacket in order to expose the ground at the tip of the probe. It gives a very short connection from the probe ground to the capacitor and eliminates noise.
Inductor Selection
The output inductor is used for storing energy and filtering output ripple current. But the trade-off condition often happens between maximum energy storage and the physical size of the inductor. The first consideration for selecting the output inductor is to make sure that the inductance is large enough to keep the converter in the continuous current mode.
That will lower ripple current and result in lower output ripple voltage. The Δ L is inductor peak-to-peak ripple current:
L
F SC The following diagram is an example to graphically
represent Δ L equation.
V OUT =1.2V, F OSC =1MHz
A good compromise value between size and efficiency is to set the peak-to-peak inductor ripple current Δ L equal to 30% of the maximum load current. But setting the peak-to-peak inductor ripple current Δ L between 20%~50% of the maximum load current is also acceptable. Then the inductance can be calculated with the following equation:
L (MA ) L
F SC L
To guarantee sufficient output current, peak inductor current must be lower than the SC5832 high-side MOSFET current limit. The peak inductor current is shown as below:
P A (MA )
L
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2.5
3 3.5
4 4.
5 5 5.5
ΔI L (A )
V IN
(V)
L=2.2μH
L=1.2μH L=1.5μH
Application Information (Continued)
Feedforward Capacitor Selection
Internal compensation function allows users saving time in design and saving cost by reducing the number of external components. The use of a feedforward capacitor C3 in the feedback network is recommended to improve transient response or higher phase margin.
C3
For optimizing the feedforward capacitor, knowing the cross frequency is the first thing. The cross frequency (or the converter bandwidth) can be determined by using a network analyzer. When getting the cross frequency with no feedforward capacitor identified, the value of feedforward capacitor C3 can be calculated with the following equation:
C
F C SS
Where F CROSS is the cross frequency.
To reduce transient ripple, the feedforward capacitor value can be increased to push the cross frequency to higher region. Although this can improve transient response, it also decreases phase margin and causes more ringing. In the other hand, if more phase margin is desired, the feedforward capacitor value can be decreased to push the cross frequency to lower region. In general, the feedforward capacitor range is between 10pF to 330pF. PCB Layout Recommendation
he device’s performance and stability are dramatically affected by PCB layout. It is recommended to follow these general guidelines shown as below:
1. Place the input capacitors and output capacitors
as close to the device as possible. The traces which connect to these capacitors should be as short and wide as possible to minimize parasitic inductance and resistance.
2. Place feedback resistors close to the FB pin.
3. Keep the sensitive signal (FB) away from the
switching signal (LX).
4. Multi-layer PCB design is recommended.
Figure 19. Recommended Layout Diagram
Outline Information
SOT-23-5 Package (Unit: mm)
Note ：Followed From JEDEC MO-178-C.
Carrier Dimensions